PLANT PROTEIN SUBSTITUTION in

DIETS for JUVENILE TILAPIA

(Sarotherodon mossambicus)

GABRIEL I. AYENI

INSTITUTE OF AQUACULTURE

UNIVERSITY OF STIRLING

STIRLING, SCOTLAND

Thesis submitted to the University in partial

fulfilment of the Degree of Master of Science

of the University of Stirling.

1981

CONTENTS

ACKNOWLEDGEMENT

ABSTRACT

INTRODUCTION

LITERATURE REVIEW

ALTERNATIVE PROTEIN SOURCES

MATERIALS AND METHODS

RESULTS

DISCUSSION

CONCLUSIONS

REFERENCES

Plates I and II

Tables I and II

Table III

Tables IV and V

Tables VI

Tables VII and VIII

Figure 1

ACKNOWLEDGEMENT

I acknowledge with gratitude my indebtedness most especially

to my supervisor Dr Kim Dauncey who with patience helped me with

corrections, criticisms and ideas, throughout the duration of this

uork. My gratitude is also due to my student adviser, Dr Albert Tacon,

for his help and advice in verious ways during my course. I also

thank the laboratory staff for their aseistance.

Finally, I thank Professor Ronald Roberts, the director of the

Institute for his encouragement throughout my stay at the University.

i

ABSTRACT

Studies were conducted to investigate the effects of three oil-seed

meals on several nutritional parameters of Sarotherodon mossambicus. and

hence determine whether they would be suitable fishmeal replacers. The

three oil seeds were sunflower seed meal, soyabean meal and rapeseed meal.

Six diets were formulated to give 30% protein. One of them was the

control, fishmeal. Three of the diets were formulated with 25% protein

supplied by each of the 3 plant sources. The remaining two diets were

all-plant protein derived by mixing the plant sources at different

proportions.

Fish of average weight approximately Q.8g were stocked at 20 per

tank. Feed was given at the rate of 5% of the total body weight per day

with regular adjustment, for 50 days.

Rapeseed meal gave the best specific growth rate, Food Conversion

ratio, Protein Efficiency ratio and Net Protein Utilization at the 25^

protein inclusion level. Its values were similar to those given by the

fishmeal. The soyabean meal also gave fairly good values, while the

sunflower seed meal generally gave poor values at the 25^ protein

inclusion level. The all-plant protein diets gave poor results similar

to those of the feed containing 25^ sunflower protein and 5% fishmeal

protein.

i i

INTRODUCTION

Aquaculturey that is the growing of aquatic organisms under

controlled conditions} can make a unique contribution to nutrition in

many parts of the world by virtue both of its extremely high

productivity in many situations and the fact that aquatic animal crops

are primarily composed of protein rather than sources of starchy staple

foods (Bardach at al.. 1972). Some aquatic organisms may be better

converters of primary food than ruminants, fowl or even pigs. These

facts have led to an almost world-wide interest, in the last two

decades, in the potential of aquatic husbandry.

In Africa, the culture of the cichlid fish known as tilapia is

believed to offer one possible solution to the nutritional problems of

the continent. Since 1924 when tilapia culture was first initiated in

Africa, there has been much progress both in the African continent and

other areas of the world such as the diddle East, South America, South

East Asia and even the Southern United States, where water temperatures

are suitable for their growth and reproduction. Tilapia are relatively

simple to cultivate, resistant to poor water quality and diseases, and

able to convert efficiently, many organic animal and agricultural waste

materials into high quality protein, hence its popularity as fish for

culture (Bardach et al.. 1972). In Africa, tilapia make up 60-70£ of

farmed fish (Shehadali, 1975). In terms of energy requirements for

aquaculture, Edwardaon (1976) suggests that both milkfish and

subsistence tilapia farming have the lowest energy requirements for

protein production. This combination of factors make tilapia an

eminently suitable spaciss for rearing in developing nations where

the problems of protein deficiency are most acute.

The supposed ease of tilapia culture has however bean exaggerated.

Thsir ability to multiply at phenomenal rates under pond conditions

leads to stunting of growth, and this disadvantage, along with marketing

problems and poor management systems caused a general disillusionment

among the farmers. This, in turn, led to a marked decline in interest

in tilapia as a cultured fish. However, in recent years the develop­

ment of new techniques through the combined efforts of the Food and

Agricultural Organisation (FAO) and other Research Centres has led to

revival of interest in the culture of this fish. Such techniques

include polyculture of tilapia with other fish species like carp and

mullet; hybridization which produces monosex tilapia (usually males)

for culture. Another is the control of reproduction through cropping

of fingerlings by predators like Oohicephalus spp.. Clarias spp. and

Hemichromis spp. The use of these techniques lead to greater overall

production, and large-sized fish by prevention of growth stunting, and

thus are becoming widespread.

Under the extensive system of tilapia cultivation the ponds are

fertilized in order to promote the provision of natural food for the

fish. In contrast, with increased intensification of culture densities

natural food alone become insufficient ad the use of supplementary

artificial feeds, in the form of pellets, becomes imperative (Van de

Lingen, 1959). The advantages of dry pellets are the possibility of

storage, availability of a consistent product, ease of handling, high

quality, high protein and energy content and controllability of feeding

rates and frequencies.

One of the most costly factors when culturing fish intensively is

feed (Kohler et al. 1978). The cost may bBprohibitive in regions of

the world such as the developing nations where many of the commercial

fish feed ingredients, such as fish-meal, are imported. Today fish-meal

constitutes an appreciable part of all commercial palleted diets for fish

(Almazan et al., 1978). The high cost of fish-maal may bo a constraint

in the future development of aquaculture. For this reason many

aquaculturists have commenced research into possible, mors economical,

replacamants for fish-meal. Numerous studios have bean conducted to

3

find alternative sources of protein and feed-stuffs, such as idhey

(fieske et al.. 1977), petroleum yeast (Iida et al.. 1970), yeests

(Appelbqum, 1977) or even insects and small prawns (lakshmanan et al..

1967). Several of these have produced good results, but their

scarcity makes their general use uneconomical.

Other researchers have concentrated on more widely available

alternative protein sources and these are more extensively considered

in the literature review.

The best solution to the provision of protein in fish feeds, in

aquaculture, therefore, appears to lie in the use of local agricultural

food-stuffs and waste products as feed ingredients.

The aim of this present study was to investigate the nutritional

qualities of three protein sources of plant origin which are widely

cultivated viz, soyabean, rapeseed and sunflower seed meals.

Evaluation of the three protein sources was achieved by progressive

partial substitution of fish-meal.

4

LITERATURE REVIEW

Members of the genus tilepia (femily Cichlidae) have been an

important source of food for man at least since recorded history began

(Bardach et al.. 1972). A study of the bas reliefs and inscriptions

on the monuments of Ancient Egypt is probably good evidence that

tilapia culture was practised before 2000 B.C. in well constructed

drainable ponds. One member of the group Tilaoia niloticus.

recognizable by the slightly rounded caudal fin, uas probably the one

cultured at that time. This species is still very abundant in the

Nile. It uas a sacred fish closely connected uith the goddess Hathor,

and symbolized the hope for rebirth after death. Also the fish Saint

Peter caught in the Sea of Galilee and those uith uhich Christ fed the

multitudes uere tilapia, probably Tilapia oalilaeus (Bardach et al..

1972).

The family Cichlidae is very diverse and uidely distributed

throughout Africa, most of South America and parts of India and Ceylon.

Tilapia are, houever, mainly indigenous to Africa uhere some 100 species

can be found. The "knoun" natural ranges have been described by

Chimits (1955, 1957), Sterba (1967), Fryer and lies (1972) and Thingrav

and Gopalakrishnan (1974).

The taxonomy of the tilapia group has come under critical revieu

in recent years. At first Van den Audeneerde (1968) proposed a

separation into three divisions, but Trewauras (1973) uas even more

radical and erectad tuo distinct genara. Her claaaification allows

separation into tha tuo distinct breeding and feeding types. This

scheme is gaining acceptance in apite of some continued adherence to

older names. The major verifying distinctions of the tuo genera era

as follows

5

Tilapia species : These are substrate spawnersthat guard the developing eggs and fry. They are generally herbivorous and have 7-16 gill- rakers on the lower part of the first arch.

Sarotherodon species : These are mouth-broodersthe fry tend to be planktophagous having a finer set of 10-28 gill rakers on the lower part of the first arch.

for the sake of clarity references to the fish as a group are denoted

by the use of the term tilapia whereas references generically or

specifically precise are denoted as, for example :

Tilaola species, Sarotherodon species, Tilapia zilli.

Tilapia melanopleura. Sarotherodon variabilis

Sarotherodon leucostictus etc.

Today no fish, with the exception of the common carp (Cvprinus

carpio). is more widely cultured than tilapia (Bardach et al.. 1972).

As early as the 1920s experiments in tilapia culture were being

carried out in Kenya. Due to the missionary efforts of such

organizations as food and Agricultural Organisation (fAO) and the

enthusiasm generated by the research of such men as H. S, Swingle at

Auburn University in Alabama and C. f. Hickling at the Tropical fish

Culture Research Institute in Malaysia, tilapia species are now

cultured at least experimentally in South east Asia, Japan, Asiatic

Russia, the Indian subcontinent, the Near East, virtually all of Africa,

parts of Europe, the United States, and many of the Latin American

countries. What has made the introduction of tilapia so successful

in this wide geographical range can be aeen in at least 14 species

which have been cultured. These species all share hardiness, ease

of breading, rapid growth, and high quality of flesh which has made

one particular species Tilaois mossambicus vary popular.

About 23 species have bean evaluated by culturists and all share

ths same important characteristics listed above. Any of these or new

6

species, or hybrids as yet untried, may prove to be the right fish for

culture in a given situation. Often problems in tilapia culture have

arisen from hasty or uninformed selection of a species (Bardach, et al.,

1972). Certain factors such as availability, food habits, salinity

and temperature tolerance, growth, reproduction and temperament have

to be considered before a species is selected for culture in a particu­

lar environment.

At present the 10 most popular cultured tilapia species are:

S. andersonii S. aureus S. aalilaeus S. spilurus nicer

S. macrochir 5. mossambicusS. nilolicusT. rendalli T. soerrmanii T. zillii

Sarotherodon andersonii is mainly cultured in Southern Africa, while

Tilapia rendallii is cultured both in Southern and Central Africa.

S. aureus is cultured mainly in West Africa. S. galilaeus. S. niloticus

and T. zillii are mainly cultured in west Africa, Central and North

Eastern Africa and the Middle East. S. mossambicus is cultured in East

Southern Africa. S. macrochir. and T. sperrmanii are cultured in

Southern Africa. S. spilurus nioer is cultured in East Africa.

Through accidental release or intentional stocking a large number

of tilapia species have now become established in the wild in areas

where they have not been indigenous. For instance the spread of tilapia

in the Far East began soon after the Second World War. It is reputed

to stem from five specimens believed to have escaped from an aquarist's

collection (Trevauras, 1967) which were discovered at Papungan, near

Kedini in East Cava (Schuster, 1952, quoted in Chimits, 1955).

i) The nutritional requirements of cultivated cold water and warmwater fish species.

Worldwide pressure to expand and develop aquaculture is motivated

primarily by the need for increased protein supply. Future interest

in aquaculture would seem to be increasing because it has been

recognised that the cultivation of fish offers certain advantages over

7

that of domesticated land animals (Hastings, 1976

One of these advantages is the ability of many species of fish to

convert prepared feeds into weight gain more efficiently than do

most terrestrial animals. Another is that ingredients in prepared

fish feeds compete less for human use than feeds for terrestrial

animals (Hastings, 1976). for such reasons the stocking of

ponds, tanks, race-ways and other water bodies with fish is common

practice today.

It was estimated that over six million tons of finfish and

shellfish are produced annually by world aquaculture (Hastings, 1976

This amount must be increased to meet the ever-increasing

demand for protein all over the world. An increase in the yield of

fish per unit area of pond can be achieved only by intensification of

the culture methods. This always means an increase in the stocking

density of fish in the pond and a corresponding increase in the

standing crop. Under such conditions the growth rate of the

individual fish is sustained at its highest level only if enough food

is available. Since the amount of natural food in the pond is

limited, it is obvious that with the increase in standing crop, the

dependence of growth and yield on supplementary feed also increases.

A most important ingredient of this feed is the protein. It should

supplement the natural proteins not only in quantity but also in

quality so as to provide a source of protein of high biological value

which will support growth.

Among the fishes cultured commercially using prepared feeds are i

Salmónida, carps, tilapias, catfishes, milkfish, tropical or ornamental

fishes, eels, grey mullets and flat fishes. The intensive cold water

aquaculture of such species as salmon, rainbow trout and some flat

fishes, like turbot and dovar sole, depende solely on artificial feed

because they are carnivorous animals. On the other hand the

cultured warm water fish such as carp, catfishss, tilapias, milkfish

ft «i: »

«**■

immnm

»mu

s

and mullet are omnlvorea feeding largely on both mlcrophytea and

macrophytea and detritus. Thus, Increase of primary productivity

by fertilization plays a significant role in their culture.

Apart from the cost of feed, another essential basic nutritional

problem ia to formulate the feed ao that it approximates as closely as

possible the nutritional requirements of the fiah. Any balanced

formula for fish diets must include an energy source plus sufficient

essential amino acids, essential fatty acids, specific vitamina and

minerals to support life and to promote growth. The majority of

research to date has been performed in order to understand the

nutritional requirements of the salmónida and cyprinida. for

example, Halver (1972) found that the nutritional requirements of tha

rainbow trout (Salmo oairdneri) change with fish size, water temperature

and with the balance of components in the ration. As dividends from

this research and development effort, practical rations for rainbow

trout can now be formulated throughout the world from locally available

dietary ingredients and can be used with a rsasonable degree of

assurance to rear rainbow trout to either market aize or to broodatock.

The same data ia not ao clearly defined for other speciae of fish and

mors work needs to be done to evaluate the specific nutrient require­

ments of cyprinids, Cichlida and several othr fishes of potential

economic importance in the tropical countrisa where shortage of protein

ia moat acute,

ii) Protein requirements

All anímala require protein for growth and maintenance. In

fiah the level needed varies with epeciea (35% for tha channel catfish

Ictalurua ounctatuai 38% for the oommon carp Cvorlnue carpió), fish

size, water quality, biological value of the protein aource and tha

accompanying non-protein energy (Garling and Wilson, 1976).

Inveetigatione of protein needs for growing fish have been complicated

by genetic differancoe batwean straina, the effects of watar

temperature end, in some cases, an inadequate test diet (Lee and

Putnam, 1973).

Proteins ere mads up of amino acid unite. All fish species

used in experiments so fsr require the some ten indispenseble

(essential) amino acids for growth (Ccwey and Sargent, 1972; hertz,

1969). These amino acids are:

arginine histidine leucinephenylalanine valine iso-leucinetryptophan threomina lysine

histidine

They must be present in the diet end must be present in balanced

relative amounts to furnish an acceptable amino acid pattern before

fish protein can be synthesised. Thus, these 10 easential amino acids

in the correct proportions are determinants for the success or failure

of any particular feed ingredient as a major protein source. fish

that are fed diets devoid of any easential amino acid fail to grow,

whereas other fish that are fed diets devoid of non-oasential amino

acids grow as well as fish fad with control diet receiving all amino

acids in the reference protein (Halver, 1972).

It can be aean from the foregoing that not only the quantity but

also the quality of protein is important in fish culture practice.

In general usage the term quality as applied to food proteins refers

to the assortment and proportions of essential amino acids. The more

complete the assortment and the more nearly the proportions approach

the physiological needs of a species for amino acids the higher the

quality of the protein (Lloyd at al. 1978)

Experiments have ahown a considerable difference in the effect

on fish growth of dietary protein from different sources. This is

quantified as differences in biological value of these proteins.

Orino and Chon (1973), working with carp, found the biological values

of proteins from animal souroes such as egg yolk (89), casein (80)

white fish meal (76) to be higher than those of proteins from

vegetable sourcea auoh as soya bean meal (74) or c o m gluten meal (55)

10

(figures in parentheses are the corresponding biological values).

Proteins are primarily used for building and maintenance of the

tissues and organs of tha fish. However in fish they also serve as

an snergy sourcs. Whether protein calories are uaed for catabolic or

anabolic purposes is dependent upon the availability of othar caloria

sources such as fats and carbohydrates. These can spare the

protein for tissue production. However, excessive dietary energy

intake may restrict protein consumption and subsequent growth if fish

feed to a sat intaka of diatary anargy (Las A Putnam, 1973). Tha

catabolism or anabolism of diatary protein also depends upon its quality.

Protein of poor quality is catabolised for the release of energy or

excess may be metabolised and storad as carcass lipid (Halvsr, 1972).

In contrast with the cold water fishes, such as rainbow trout,

little has been determined concerning the protein requirement and anargy

utilization of tilapia. Research in this field is very important in

view of the recent increase of the culture of tilapia.

S.moasambais has been shown to require 50% dietary protein for

maximum growth on first feeding, 40% at weights from 0.5 - 10g, 35%

between 15 - 50g and 30% at fish weights over 50g (Jauncey, 1981,

Pars. comm.).

nazid at al (1978) have also determined that T. zillii has a

qualitative requirement for the same tan essential amino acids reported

necessary for the growth of other fish species,

iii) Lioid requirement

Fats and oils are high energy oompounds. They are therefore a

ready source of anorgy for fish. In most forms they are 85 - 90%

digestible and successful fish feeds oontain from 4 - 1 8 % fat (Hastings,

1976). Tat as an anargy source has a protein-sparing action which

enables the fish to utilise the protein for maximum growth. Thus fats

are an especially useful ingredient in foods of fry and young fish where

higher energy intake is neceasary to promote more rapid growth.

Apart from aerving aa the principal energy source, dietary lipida

play important role8 in the nutrition of warm water fiahea by providing

phospholipid and steroid components of vital organa, and in maintenance

of neutral bouyancy.

Essential fatty adds

These are fatty acida of the omega -3 and omega -6 series required

for maximal growth and normal tissue deposition in fish. The fish

cannot synthesize them and they must be supplied in the diet.

Essential fatty acid requirements have been demonstrated for several

species of fish. Tor rainbow trout linolenic acid (18:3 3) will meet

the fatty acid requirement at 0.8 - 1.0% of the diet or 1.66 - 2.7% of

dietary anergy. (Sinnhuber et al. 1972; Watanabe at al. 1974).

However marine fiahas such as red seabream (Paourua major) and turbot

(ScoDhthalreus maximus) are apparently unable to convert linolenic acid

to longer chain polyunsaturated acida at rates needed for normal growth.

These omega 3 fatty acida must therefore be supplied pre-formed in the

diet (Yone and Fugii, 1975; Cowey, 1976) principally as C22 fatty acids.

A recent study (Kanizawa et al. 1980)has shown that, unlike cold water

species, Tilaoia zillii utilizes omega 6 fatty acids, rather than

omaga 3, as an*essential fatty acid source, the requirement being 1% of

the diet.

Fats in fish food must be accompanied by sufficient choline,

methionine and tocopherols for efficient metabolism. Fats altered by

oxidation or hydrogenation may function as energy sources but not as

sources of essential fatty acids (Hastings,1976). To avoid oxidation

of fats to aldehydes, ketones and acids (which cause toxicity and loss

of vitamins in foods) antioxidants ars recommended in prepared fish

feeds e.g. alpha-tocopherol (Vitamin C) (Hastings, 1976).

lv cwfthrflHtf nil

Carbohydrates are another aourea of energy that may have a protein

sparing action. Exoaaa dietary carbohydrate is partially etored in the

livar aa glycogan and partially convartad into viscaral and auacular

fat. Carbohydratas rafar generally to the nitrogen free - axtractivaa

(NFE) portion of a feed and are calculated aa the difference between

100% and the sun of protein, fat, fibre, and moisture. NFE is

considered to have an average digestibility approximating that of

starch. Carbohydrate is an inexpensive energy source compared to the

cost of protein and fat for this purpose. The range of carbohydrate

levels found in prepared fish feeds rangss 10 - 50% and ths efficiency

of utilization as energy varies from 40 - 99% (Hastings, 1976).

There is still much controversy surrounding ths efficiency with which

dietary carbohydrate is utilized by fish and soma studies of carbohy­

drate metabolizing enzymes have indicated that fish resemble diabetic

higher animals (Cowey & Sargent, 1972; Cowey & Sargent, 1979).

v) Vitamins and mineral reoulreaents

Dost of the nutrients known as vitamins for terrestrial animala

are required by fish (Hastings, 1976). Lack of vitamins cause deficiency

diseases in fish. Vitamin deficiency dieeasas have been described for

many speciae of fiah (Halver, 1972).

Commercial and test fish feeds contain vitamins as a premix

additive compounded by special formulation, as shown in Table III.

To avoid lose in processed and stored feeds, vitamins may be added as

a spray after manufacture or procured in the water* repellent form which

protect them from chemical change even during the proceas of expansion

palleting (Hastings and Simco, 1973).

Minerals are also Important components of the diet of fish.

Little is known about the trace mineral requirements of fish. Macro

mineral requirements have been studiad with a few species under care­

fully controlled experimental conditions (NAS/NRC, 1973). Mineral

additione to a formula for feeds to be used in salt water are somewhat

laae than for those used in freshwater. Most watere contribute

ionized mineral compounds which era exohangsd through the gills and

13

skin with thoss in the fish body by simple diffusion, enzymatic action,

metabolic carriers or special cellular selection (Hastings, 1976).

A mineral premix that supplies all the known requirements of fish

is presented in Table III. Vitamins, minerals, non-digestible

components, and food contaminants in the diet are regerded as

non-energy components because the energy derived from them is

negligible and are usually not considered as contributing calories to

the diet.

14

ALTERNATIVE PROTEIN SOURCES

Sines protein is generally regarded to be the single most

expensive dietary ingredient, its source of regular supply is very

crucial to the success of modern aquaculture practice. At present

the major aource of this protein is fish-meal, and among the more

successful fish production diets used to date, none has contained

less than 10% fish-meal (Halver, 1972).

This dependence on fish-meal as an aesential ingredient in warm

water fish feed imposes soma difficulties on the development of fish

culture and its intensification. Fish-meal is not only more expensive

than many proteins, but its supply is much less reliable. Often there

is a shortage of supply which forces the prices to rise in the market

and there is no assurance that this trend will not continue in the

future. In contrsst, reliance on alternatives such as plant protein

sources may be more economical and successful since plants can be

intensively cultivated, ensuring uniformity of supply,

i) Non-protein nitrogen (NPN)

Various non-protein nitrogen compounds have bean thought of as

possible supplements to fiah-neal as a aource of food for fish. It is

well known that ruminants can utilize non-protein nitrogen instead of

true dietary protein (Hepher, 1978). The primary non-protein nitrogen

compound uaed in cattle feeding is urea. This changes in the rumen

into ammonia which is utilized by bacteria to form cellular protain

which in turn la uead as eouroe of protein by the animal. Exparimanta

have shown that high yialde of milk could b* obtained from cows fad

purified rations in which the only souroa of nitrogen was urea and

ammonium salte, but the usual practice is that not more than one-third

of the total protain equivalent should eome from urea (Coppock and Slack,

1970). Many workers have triad to find whether this source of nitrogen

could also aarve as a protain replacement in warm water fish diets.

15

This possibility is dubious if the dependence of the fish on fish-meal

and essential amino acids is taken into account (Hepher, 1978).

Nevertheless a few studies have ehown such a possibility with the

grey mullet, Leary (1970) reported that urea can replace protein at

least in part, in the diet of mullet. Further experiments to determine

if it ia possible to tranaform non-protein nitrogen into protein in the

gut of warm water fish were conducted on carp at the Fish and Aquacultura

Research Station at Dor Israal (floaz at al. 1977). Tha rasults show

conclusively that carp cannot utilize urea. This conclusion is strongly

supported by the results of an experiment carried out by Kerns and

Roalofs (1977) who substituted dried poultry wastes for fish-meal in the

diet of carp. Although the diets tested by these authors wars

iso-caloric and equal in nitrogen levala, the poultry waate diet gave a

much lower growth rate. Lu and Keveren (1975) also obtained a much

lower growth rata from catfiah with increaaing levels of poultry wastes

in the diets. The conclusion from these observations is that it seams

that at least carp and catfish, of the warm water fish, cannot utilize

non-protein nitrogen aa a cheap protein eource and a replacement for

fish-meal. Investigation of the use of non-protein nitrogen by tilapia

should be carried out before a general atatement concerning warm water

fiah could be made,

ii) Aloal protein

The unicellular algae are a class of plant proteins that have bean

considered for the replacement of fiah-meal in fiah feeds. The most

common single-call algae produced in mass cultures and which, therefore,

can be used as a feed ingredient are Chlorella. Scsnedesmus and Soirulinc.

Under uncontrolled eonditiona the culture of other algae species like

Euolana. Oocvetls and Plicrotinlum may prove economical. The dried oell

material of most of theae algae contain 50 - 69* protein (Taaiya, 1975)

and if provided with sufficient nutrients and light, algal cultures can

produce very high yields. Retovsky (1966) states that currently 110g

of Chlorella dry mattsr can ba harvested daily from a 1-m2 araa of

production unit. Extrapolated to common land unite, this equals

396 ton/ha/yr. The production of protein will than ba savaral thousand

fold greater than by tha usual form of agriculture. Thus a successful

replacement of fish-meal by algae would indicate a brighter future for

warm water fish husbandry.

The use of unicellular algae as feed for warm water fish has bean

studied in a number of experiments (Terao, 1960; Ahmed, 1966;

Anonymous 1969; Reed et al. 1974; Stanley and Donee, 1976; neska and

Pruas, 1977). dost of these studies although conducted on email

samplea and in aquaria or tanks, showed good reaulte. The fish were

able to utilize the algae, quite efficiently as a source of protain.

It would thus be nacesaary to carry out these experiments under field

conditions as aquarium conditions are not exactly the earn as pond

conditions.

However the high cost of the algae was the main drawback from a

practical point of view. The production of aingle cell algae ia at

preaent too expensive to be competitive with exiating protein sources.

The main difficulties encountered in thia reapect were:

i The coet of production unit and the nutrients

ii Tha method and costs of harvesting

iii The coats of drying the harvested algae.

Recent work carried out in Israel on the culture of algae on waste

water have shown that the economic problems can be overcome (Shelef et al.

1976). The reeulte indicated that sufficient algae nutrients are con­

tained in one litre of domestic waste water to support tha growth of 500

to 1000mg of algae dry matter (Shelef et al. 1966). The system is an

integrated process in which the algae fix C02 and release 0j by

photosynthesis.

This 02 is used by bacteria in oxidising the organic matter while

tha baotaria produce auffieiant C02 and nutrients for tha algao. Sines

17

both wests water treatment and the integral culture aystem share the

cost of algae production and due to improved methoda of harvesting and

drying, it is believed that algaa meal produced in this way can be

economically competitive with other protein sources for animal feeds.

Multi-cellular algal meal:

Researchers have also looked into the possibility of using

multi-cellular algaa to replace fish-meal. Stanley and Donas (1976)

investigated growth in bigmouth buffalo Ictlobua cvprlnellus. blue tilapia

Tllapja aurea and graas carp CtanoDharvnoodon idella which had been fed

fresh algaa. The conclusion drawn from thair axparimanta is that growth

obtained for blue tilapia and bigmouth buffalo suggests that aquaculture

with Spirulina is feasible.

Mathavan et al. (1976) also reported the results of feeding algee

to Tilapia mossambicus. Soiroovra maxima, a natural food of Tilapia

mossambicus. (Chacko and Krishnamurth; 1954) was ehoaan aa plant food,

while goat liver and frog'a tadpole (mobile pray) size 25mg) served as

animal food. The authors concluded from their study that to ensure

"true growth in herbivorous fishes, animal matter is essential and that

a hsrbivoroua fiah neither will nor can consume and utilize sufficient

amounts of algae to meet its metabolic energy demands". This

conclusion ia fallacious and unscientific in that, by definition, a

herbivore does not consume animal matter. In addition the authors

have insufficient data to support this sweeping statement and should

only have concluded that their particular animal protein diets ware

superior to Solroovra. In addition, this conclusion contradicts the

results of many recent experiments such as Stanley end Jones (1976) which

have shown that tilapia can derive sufficient nutrients from some

filamentous algae for adequate growth. The contradictory results

obtained by these authors might be due to an improper balanee of amino

acids in the teat diet they used.

Another teat conducted on the replacement of fish-meal with diets

1B

containing algaa was carriad out in tha Soviat Union by Plironova in

1975. In thasa experiments tha author teatad tha nutritive value of

the protococcal alga Kirchnerlella obese aa feed for tilapia. The

testa involved rearing tilapia on 8 vegetable/meat and bona meal mix­

tures. Tha author concluded that when Tilapia is fad on vegetable

feed the availability of tha feed and tha growth rata of tha fish

increase aa the proportion of Kirchnarialla obesa in the feed mix ia

increased, which confirms tha previous conclusion on tha nutritive

value of algaa totilapia.

iii) Other plant proteins and by-products

Pantastico and Baldia (1976) studied supplemental feeding of

Tilapia moasambicus at Laguna da Bay in the Philippines. Thair aim

was to find an economical and* nutritious food for tilapia. The fish

ware cultured in floating enclosures to minimize the problem of over­

breeding since fry escaped through tha nets. Whilst natural food

abounded in tha lake it was still nacaasary to determine if tha growth

rats and protein quality could be improved by supplemental feeding.

Tha mean weight of tha fish used was about 10g.

Economical and nutritious aupplaaantal feeds ware prepared using:

i rica bran - ipil - ipil - fish-meal 60 : 20 : 20 (feed 1)

ii chopped snaila - rics bren 30 : 70 (feed 2)

The feeds wars ground finely, moistened, pelletized and sundried.

Feeding level was 10jt of tha body weight adjusted monthly. Feeds ware

given once a day during the first month of the experiment. Later

feeding waa given twica daily, onoe in tha morning and tha other in the

afternoon. Tilapis without supplemental feed were maintained as

control. Tha experiment was conductsd for 90 daya. The results show

that Tllaola moaaamblcus given supplemental feed showed significantly

faster growth as oompared to the control. Of the two rations tested,

feed 1 gave improved growth. This was attributed to the higher protein

oontsnt of food 1 (23.81%) as oompared to food 2 (12.73%).

19

In another related experiment the effect of varying levela of

ipil - ipil on the protein content of tilapia was determined. Ten

fingerlinga were stocked in 60-litre capacity aquaria with tap water,

tilater was changed every two days. Initial length - weight

measurements ware taken. Dried and finely ground ipil - ipil

(Leucaena leucocephala) leaves were given at 3 levels adjusted monthly:

(s) 3% (b) 6% and (c) 9% of the body weight were fed.

The results showed the beneficial effect of feeding Tilapia moseambicus

with varying levels of ipil - ipil leafmeal. The crude protein

content of tilapia increased proportionately with the levels of

feeding.

Tha authors concluded that the protein gain obtained with ipil -

ipil feeding is highly encouraging considering that this type of feed

could be given at a very minimal cost.

Bayna at al. (1976) made a study of supplemental feeds containing

coffee-pulp for rearing tilapia in El-Salvador, Central America. In

their experiment, 3 prepared feeds wars evaluated, each with a similar

basic composition. Two of the 3 feeds contained 30% coffee-pulp, and

the third feed contained compensatory quantities of wheat bran and

ground corn and no coffas-pulp. All feeds wars formulated to contain

approximately 20% crude protein. This protein level is well below the

optimum for tilepie (Cruz end Laudencia, 1977). The feeds were then

fed to Tilepie aurea.

findings from these etudies demonstrated that coffee-pulp is en

adequete substitute for wheet bren end ground corn in e supplemental

diet for Tllapls auras at levels up to 30% in the feed.

Kohler end Pegen-font (1976) reported the results of e study

conducted on using rum distillation wastes, pharmaceutical wastes and

chicken feed for rearing Tilepie auras in Puerto Rieo.

Distiller's solubles are the major waste product resulting from

the rum distillation process. The by-produet is high in organic

20

content (Hill at «1. 1963) and has bean uaad as an agricultural

fertilizer (Innas, 1951). In addition to the rum distiller's solubles,

dead yeast cells collected from the bottom of the distillation vats,

wars evaluated in the study. 'Spent beers' are pharmaceutical wastes

the expended media in which strains of bacteria were cultured for the

production of antibiotics.

Twenty-four plastic pools were used as the experimental units.

Each was about 0.9m in depth and 3.7m in diameter. The experiment

consisted of 8 treatments with 3 replications for each treatment.

Each pool was stocked with 10 Tilaoia aurea fingerlings. The mean

weight per stocked fish was 1g. The rum and pharmaceutical wastes

were applied concurrently to their respective pools in their raw,

viscous forms approximately every 2 weeks. The chicken feed was

applied as fertilizers.

The results showed that the fish from the spent beer treatment

attained the highest weights. The mean standing crop was near that

of the fish which fed on the commercial fish fead, and was over 4 times

that of fish from the unmanaged system. It resulted in no adverse

effect to the fish or the quality of water. The fish fed the rum

distiller's solubles yielded a mean standing crop at harvest that was

twice that of the unmanaged system. In the rum distiller'a yeaet

treatment, there was more than three fold increase of fish weight

over that of the unmanaged system. However, it resulted in poor water

quality conditions.

If the wastes were not fed as fertilizers in the raw form as

already indicated, but were harvested, dried and incorporated into a

dried feed, their utilization and concomitantly water quality would

probably be improved.

The investigators concluded that with the exception of the spent

beer, it is doubtful that the raw waste produots would be more

economical than intensive fertilization using inorganic aeureee.

21

Cridland (1960) of Cast African Fiahariaa Research Organization,

Dinja, Uganda conducted a study of the value-of various foods fed to

Tilapia esculents. Hs used fry that had an average length of 14.8mm

and average weight of 0.044gm. The fish wars fad twice daily at

regular intervals with as much as they could consume.

In the feeding experiments glass aquaria which contained 12 litres

of water, were used. The feeds used included animal flesh and plants

such as the following:

Oligochaete worms (Stvhlmania sp)Liver of either sheep or cows Beef muscle The flesh of tilapia The flesh of PlormvrusThe stomach content of tilapia (phytoplankton)The stomach content of Wormvrua (insect larvae)Larvae of Chironomua oulcher UiedmannDaohnla maona StrausPrawns (Caridina nllotica Roux)Splroovra sp.Euolana sp.BemaxBoiled maize meal.

Results indicated that the best growth was obtained when the fish

were given a mixed diet, but certain whole organisms gave similar results.

Fish fed exclusively on oligochaete worms grew almost as well as fish fed

on a more elaborate diet. The author attributed this to all essential

requirements provided by the worm and believed that their gut contents

provided any elements that.might be lacking in the tissues of the worm

themselves. Fish fed exclusively on certain animal tissues such as

beef and tilapia muscle did not grow well and developed abnormally. It

is interesting to note that while a similar rate of growth was made by

fish fed on flormvrus muscle they developed normally. Thus the result

schisvsd with bssf and tilapia muscle as feed was probably due to

inadequate balance of amino acids in the feed which could not mast the

raquiramanta of the fish.

A dist composed of algae Including diatoms which ara the principal

natural food of Tilapia aeculenta did not give as good rasults aa a diet

containing a high proportion of aniaal protain.

Highly farinaceous food such as bemax and maiza gave poor reaulta.

Initially bemax appeared to be the batter food. Pish fad on this product

reached a length of 7.0cn and a weight of 4.5g in aix months but after

four months they started to develop abnormally and ahowed deformations

of the head and were flabby and pale in colour. They showed a high

mortality rate and after six months all of them had died. Fish fad on

maize meal made vary poor growth and only reached a length of 4.5cm and

a weight of 1.7g after 12 months which is the poorest result with any of

these foods. After thrae months these fish also developed daformationa

of the head and tail and their eyaa became protuberant.

Obviously the growth in the fish fed bemax and maiza meal was poor

dua to the low laval of protein in the two feeds. The diseases were

probably deficiency diseases caused by lack of certain vitamins. Thus

the use of bemax and maiza maal as single ingredient feed should be

discouraged.

However maize can be successfully used as fish feeds if mixed with

other ingredients with high level of protein as shown in the following

example. Flabaye (1971) atudiad the growth of Tllaoia mossamblcus in

which he uaed 3 feeds.

Feed 1 t 60% maize meal, 20% groundnut cake and 20% fish-meal and penicillin (60mg/kg of food)

Feed 2 > The same as feed 1 but no penicillin.

Feed 3 i 80% maize meal, 20% fish-meal and no penicillin.

There were 8 fiah par tank.

Fish ware fed a dally ration of 5% of their total body weight, twioe a day.

The resulta showed that there was no significant difference between

the mean weight gain of fish fed on foods 1 and 2. There was however a

significant difference in mean weight gain between feed 2 and 3.

The author concluded that addition of groundnut cake to maize meal

23

in correct proportions to givs a ratio of digestible protein to

carbohydrate of approximately 1 : 2 increases the rate of growth of

T. mossambicus. The addition of penicillin as a biostimulant to

this maize meal plus groundnut cake diet did not produce any

significant difference in the rate of growth of the fish,

iv) Oil-seed meals

Plant proteins include the by-products of the oil-seed industry

and comprise principally the presscake and extracted meals from soya­

bean, peanut, sunflower, cottonseed, linseed, rapeseed, coconut and

groundnut.

Many of the oil-seeds have been evaluated as possible substitutes

for fish-meal in catfiah, carp and the sslmonids, but only few studies

havs been documented for tilapia. The principal reaeon for the interest

in oil-seed meals as dietary protein sources for fish lies in their

relatively high protein content (40 - 50%) compared to other plant

materials. Following are some investigations that havs been conducted

on oil-seed meals

Wu and Dan (1977) reported the reaulte of investigation they

conducted on the possible use of 2 oil-seed meals and other proteins as

feeds for Tlleole auree.

The teat diets contained 25% of crude protein in form of fish-meal,

casein, soyabean meal, peanut cake and yeaat individually.

The experimante were performed in aquaria stocked with 20 - 30 fish

each. Feeding rate was S* of the total body weight given 3 times daily.

The experiments lasted for 4 weeks.

The results showed that casein, followed by fish-meal gave the

highest body weight gain, protein efficiency ratio (PER) and net-protain

utilization (NPU). Fish fad on ooyabean meal had a weight gain of about

65* of that of fiah-moal. Fiah fad on peanut caka had a weight gain or

about 29* of that of fiah-meal while fiah fad on yaaat only had about

18* of the weight produced in fish fad on fish-meal.

The protein efficiency retio end net-protein utilizetion of the

different diete ere ee follows: casein end fish-meal had the beet

nutritional value. Theae ware followed by soyabean. Peanut cake and

yeast diats had poor values.

From these it can be concluded soyabean meal rather than peanut

cake would be an efficient fiah-oeal replacar at the 2536 crude protein

levels among the two oil seeda.

Oauncey (Ph.O Thasia 1979) investigated the substitution of

fish-meal by aoyabean in the diet of fingerling mirror carp (Cvcrinua

caroio). In this study he formulated 7 diets on an isonitrogenous

and isoenergatic basis to supply 30% protein and 3.4 kcal/g of

metabolisable energy.

The proportion of the dietary protein supplied by each protein

aourca was varied with percentages of fieh-meal protein and soyabean

protein in the following ratios: 30:0, 25:5, 20:10, 15:15, 10:20,

5:25, and 0:30. Tan fiah were stocked in each tank and the faada ware

fed to duplicate tanka at the rate of 4% of the body weight per day far

5 weeks.

The results showed that in a 30% fish-meal protein diet

substitution of only one third of the protein with soyabean protein

concentrate caused a significant decrease in growth rate and food

utilization. The author concluded that, however, it ia poaeibla that

this might be offset by tha reduction in feed coats achieved by replacing

fish-meal with soyabean.

These results are in agreement with previous studies of the

isonitrogenoua replacement of fish-meal with soyabean protein.

For example Cowey at al. (1971) replaced approximately half of tha

protein in 4036 cod-maal protein diet, with soyabean meal and found that

this depressed the growth and protein utilisation of plaica (Plevronectes

Plateaaa).

Andrews and Page (1974) have also reported similar raeults for

The protein efficiency retio end net-protein utilizetion of the

different diete ere es follows: casein end fish-meel had the best

nutritional value. These were followed by soyabean. Peanut caka and

yaast diets had poor values.

From these it can be concluded aoyabean meal rather than peanut

cake would be an efficient fish-meal replacer at the 25% crude protein

level, among the two oil seeds,

3auncay (Ph.O Thesis 1979) investigated the substitution of

fish-meal by soyabsan in the diet of fingerling mirror carp (Cvorinua

carpio). In this study he formulated 7 diets on an isonitrogenous

and isosnergetic basis to supply 30% protein and 3.4 kcal/g of

metabolisable energy.

The proportion of the dietary protein supplied by each protein

source waa varied with percentages of fish-meal protein and eoyabean

protein in the following ratios: 30:0, 25:5, 20:10, 15:15, 10:20,

5:25, and 0:30. Tan fish were atocksd in each tank and the feeds wars

fed to duplicate tanks at the rats of 4% of the body weight per day for

5 weeks.

The results showed that in a 30% fish-meal protein diet

substitution of only one third of the protein with soyabean protein

concentrate caused a significant decreeae in growth rate and food

utilization. The author concluded that, however, it is possible that

this might be offset by the reduction in feed costa achieved by replacing

fish-meal with eoyabean.

These results are in agreement with previous studies of the

isonitrogenous replacement of fiah-meal with eoyabean protein.

For example Cowey at el. (1971) replaced approximately half of the

protein in 40% cod-meal protein diet, with eoyebean meal and found that

this depreeaed the growth and protein utilization of plaioe (Plevronectea

pletoaaah

Andrews and Page (1974) have alee reported similar results far

25

channel catfish Ictalurua punctatua where isonitrogenous replacement of

dietary menhaden-meal with soyabean meal depressed growth and food

utilization even when the soyabean meal was supplemented with methionine,

cystine and lysine to the levels found in the fish-meal control.

Koops et al. (1975) studied the utilization of soyabsan protein by

the rainbow trout (Salmo oairdneri). They used isocaloric feed rations

with crude protein levels of 47% and 39%. They found that heavy growth

depressions occurred in rainbow trout, if fish-msal is entirely replaced

by soyabean protein. When equal quantity of food was fad the feed

conversion for soybean (2.5 - 3.0) was roughly double that of fish-meal

(1.3 - 1.4) and the weight gain was less than half. Addition of amino

acids did not influence the feed conversion. Furthermors the trout

rejected the soyabean rations because of taste. This could be

compensated only partially when soyabean oil was replaced by red fish

oil.

In a second experiment 25% of the fish-meal protein was replaced

by the soyabean concentrate "Heypro". Here the soyabean was supple­

mented by methionine as well as animal protein. In this case feed

conversion and growth rate were as favourable as in the control ration.

Adding of amylolytic enzymes to the Haypro-ration did not yield any

improvement of the result.

The authors concluded that rainbow trout can utiliza aoyabaan

protein if supplemented by methionine and animal protein.

Brandt (1979) conducted a atudy to determine if channel catfish

and golden shinere could uae soyabeans processed by the heating method.

Such beano are termed full-fat cooked eoyabeans. Prior to thie the

problem confronting researchers is how to economically destroy the

growth inhibitors present in eoyabeans which presumably ere responsible

for the depresalons in growth earlier discussed.

Six experimental diets ulh varying proportions of fieh-meal and

full fat oooked aoyabeans were fomulstsd to contain 33 - 34% protein.

25

channel catfish Ictalurua punctatua where isonitroganous replacement of

dietary menhaden-meel with soyabean meal depressed growth and food

utilization oven whan the soyabean meal was supplemented with methionine,

cystine and lysine to tha levels found in the fish-meal control.

Koops et al. (1975) studied the utilization of soyabean protein by

the rainbow trout (Salmo oairdneri). They used isocaloric feed rations

with crude protein levels of 47% and 39%. They found that heavy growth

depressions occurred in rainbow trout, if fish-asal is entirely replaced

by soyabean protein. When equal quantity of food was fed the feed

conversion for soybean (2.5 - 3.0) was roughly double that of fish-meal

(1.3 - 1.4) and the weight gain was less than half. Addition of amino

acids did not influence the feed conversion. Furthermore tha trout

rejected the soyabean rations because of taste. This could be

compensated only partially whan soyabean oil waa replaced by red fish

oil.

In a second experiment 25% of the fish-meal protein was replaced

by tha soyabean concentrate "Haypro". Here the soyabean was supple­

mented by methionine aa well as animal protein. In this case feed

conversion and growth rate were as favourable as in the control ration.

Adding of amylolytic enzymes to tha Haypro-ration did not yield any

improvement of the result.

The authors concluded that rainbow trout can utilize soyabean

protein if supplemented by methionine and animal protein.

Brandt (1979) conducted a study to determine if channel catfish

and golden shinere could use soyabeans prooeaaed by the heating method.

Such beans are termed full-fat cooked soyabeans. Prior to this the

problem confronting researchers is how to economically destroy the

growth inhibitors present in soyabeans which presumably are responsible

for the depressions in growth earlier discussed.

Six experimental diets wJh varying proportions of fish-meal and

full fat oooked eoyabeans ware formulated to contain 33 - 34% protein.

26

The fish wars fad st tha rata of 3£ of thair body weight par day»

6 days a weak.

The results showed that there ware no significant differences in

tha average weight of fish receiving tha different feeds. From this

the conclusion can be drawn that fish-meal can be successfully

replaced both partly and completely by full-fat soyabeans.

It was also found out from this study that as bean processing

treatment increases from 170 to 207°C the use of full-fat soyabeans

by catfish decreases slightly. No problems were encountered in feeding

the golden shiners a 100$S full-fat soyabean diet» the soyabeans were

readily consumed by the fieh.

Rapeased

Rapeseed is one of the potential leading sources of food protein

because of the production capacity of the crop and nutritional value of

the protein. The essential amino acid composition of rapeseed protein

compared favourably with that of soyabean. For this reason many studies

have recently been conducted on the possible use of rapeseed meal as a

fish-meal protein substitute in fish diets.

In Poland» Dabrowaki and Kozlowska (1980) studied the possibilities

of fish-meal substitution by rapsssed meal in the diet offered common

carp. Experimental diets were prepared by substituting rapeseed meals

for 50 or 100)1 of the fish-meal protein. One hundred fish were stocked

per tank in 1400 litre capacity. Average size of fish used was 2.5g.

The fish were fed by hand at the rate of 4% dry diet per wet body

weight for 74 daya.

The reaults showed that 50)1 of fish-meal protein can be substituted

by rapaeeed meal protein without a significant drop in fish performance.

It can thus be concluded that rapeseed is an efficient fish-meal replaoer.

However tha rssulte of other investigations conducted do not justify this

conclusion

For example, Yurkowski at el. (1978) indicated that the rapeeeed

or rapeeeed flour aupplied to rainbow trout at levels of 72.3% and

64.7% respectively significantly reduced fish growth.

Also in West Germany, another attempt with rdnbow trout has shown

that even adding 5% rapeeeed impairs feed utilization, and when supplied

at the levels of 10% and 20% of the diet increases the Taluctance of

fish to eat food (Anon 1979).

Higgs et al. (1979) worked with Pacific salmon and rapaseed meal

in diets containing levels of 9%, 11% and 22%. Fish gain and diet

utilization were slightly reduced only at the highest ratio of rapeseed

meal in the diet. In addition, thyroid hypertrophy was observed in

fish fed a diet composed of 11% and 22% rapesaed meal.

The results so far obtained are inconclusive mainly due to

superficial characteristics of the rapeseed.

Rapeseed is contaminated with toxic substances among which

glucosinolate derivatives that can have harmful affect on animal thyroid

fland. Furthermore typical crude fibre content of commercial rapeseed

meal is 13-16% which is an unfavourable factor.

It appears that the rapeasad meals used in the experiments already

mentioned originated from different strains with varied glucoainolate

levels, hence the inconsistent results. Glucosinolate, which is a

growth inhibitor, can however be reduced or eliminated by preventing

its hydrolysis through inactivation of myrosinase. For example it has

bean shown with mammals that higher digestibility of rapeseed meal can

be obtained by heat treatment which inactivates myrosinaae.

The conclusion that can be drawn from the foregoing is that

efficient utilization of rapeeesd in fiah diets can be achieved by

heat treatment or by use of rapesssd with a low level of glucosinolataa.

MATERIALS AND METHODS

Experimental system and animals

This experiment was oonducted in the Tropical Aquarium of the

Institute of Aquaculture for a period of 50 days. The experimental facility

employed was made up of a warm water recycling system, consisting of twelve,

9 litre, self-cleaning circular tanks which drained into a 200 litre solids

3 3settling tank and then into a 0.5m filter tank containing 0.3m of 0.5 -

1.0cm gravel. Water was pumped from the base of the submerged gravel

filter into a 120 litre heated, aerated, header tank from which it flowed

into the experimental tanks each of which received a flow of 1.5 litres/min.

The header tank was vigorously aerated so that the level of dissolved oxygen

in the experimental tanks did not fall below 90% saturation. Fresh water

was added to the eystem at a rate of 0.25 litres/min. to replace splashing

and evaporation losses. The temperature was maintained at 27°C - 1°C by a

3Kw immersion heater placed in the header tank and controlled by a thermis­

tor sensor via a proportional output circuit designed and constructed by the

Shared Technical Services Department of the University of Stirling (see

Plates 1 and II).

The species of fish used in this study was Sarotherodon mossambicus

(Peters). The juveniles of the fiah ware produced in the Institute from

stock that had bean idantifiad as genetically purs by starch-gel

electrophoretic typing (McAndrew, B. Personal communication 1981).

DietThe plant protein sources used in the experiment were sunflower seeds

(Hellanthus ennuus L.), raoeseeds (Brassica spp) and soyabean (Glycine epp).

Supplied es deeortioeted mechanically oil extracted (expressed) meals by

Erith Oil Works Ltd., Church Manor Way, Erith, Kent. These plant materials

were selected for this study because a literature review revealed that,

apart from soyabean, they have not yet been evaluated in diets for many warm

water fiah species.

29

The raw materials ware ground in an electric coffee grinder and

then passed through a 1mm sieve to obtain a fine powder of each.

Tha proximate analysis of the sunflower seeds, rapeseeds and

soyabean, and the herring fishmeal were then performed prior to diet

formulation to obtain the following:

i Moisture content - by loss in weight on drying at 105°C for 24 hours

li Crude protein - by micro Kjsldahl method

iii Crude lipid - by Soxhlet ether extract method

iv Aah - by measuring rosidus after heating at 450°C for 12 hours

v NFC (nitrogen free extractives)- obtained by eubtracting above

values from 100.

Diet preparation

Six diets were prepared by combinations of varying proportions of

the three plant materials with the herring fishmeal, to give 30% protein

in every caee. The levels of dietary aunflowar rapeaeeds and aoyabean

and the white fiahmeal needed to provide the required dietary protein

level (30%) were then calculated and tha lipid and NFC eoapounda ware

balanced by cod liver oil, mineral aixtura and atarch reapactively aa

ahown in Table III.

The dieta ware prepared by thoroughly mixing of the dry ingredienta

with the oil and than adding cold water until a atiff dough reaulted.

This was then paaaed through a mincer with a 3mm die and the resulting

'sphagatti-like' strings were dried in a forced convection sir-dryer at

35°C. After drying tha diets were broken up and sieved into convenient

pellet sizes. Diets ware stored at -20°C until required.

F eedino

Prior to transfar to tha experimental tanks the fish ware 72 days

post-raleaao and had been roared on a commercial trout ration ('Omega',

3Q

Plates I and II

The water recycling system in the Tropical Aquarium, University of Stirling

31

TABLE I : Analysis of Plant materials

Protein Lipid Floiature Ash NFE

Sunflower 31.1 2.8 1.4 13.6 51.1

Rapeaeeds 3B.6 1.7 1.3 14.4 44

Soyabean 48.7 2.2 1.7 13.6 33.8

Fishmeal 68.9 10.4 1.0 10.7 8.0

TABLE II i Proportion» of Protein supplied by inoradianta In experimental diets

Diet Ingradianta

1 Fishmeal (30%) - Control

2 Fishmeal (5%), Sunflower (25%)

3 Fishmeal (5%), Rapeaeeds (25%)

4 Fishmeal (5%), Soyabean (25%)

5 Rapeaeeda (15%), Soyabean (7.5%),A Sunflower (7.5%)

6 Soyabean (1SJ6), Rapaaaad (7.5%),A Sunflower (7.5%)

Edward Baker, Sudbury, Suffolk, Great Britain). Fiah were atocked at

21 par tank for 2 weeks prior to the experiment to acclimatise them to

the conditions of the recycling system. At the beginning of the

experiment the fish were redistributed at 20 fish par tank with average

individual fish weight per tank being about 0.9g.

A fixed feeding regime of 5$ of the body weight per day (dry food/

whole fish) divided into 3 equal faeda was adopted. Feeding was done

in the morning, afternoon and in the evening. Each diet was fed to

randomly assigned duplicate tanks of fish. Feeding was performed for

nine consecutive days with no food being given on the tenth day when the

fish were weighed.

The necessary adjustment in the quantity of food fed was made at

the end of every weighing period.

Weight determination

Small hand nets ware uaed to remove the fiah from the axparimantal

tanks and than they were placed on a paper towel to remove exceaa

moiature before being tranaferred to a balanoe where their weight waa

recorded. The method of anaeathetizing the fiah by uaing 0.5g of

benzocaine in 1,500ml of water (Rosa and Geddea 1978) waa not uaed because

this may cause mortality in the fiah through undue stress. Therefore

the lengths of individual fiah wera not recorded and the condition

factor (k) was not calculated.

The weights recorded were used to calculate various parameters for

each weighing period end averaged over the whole experiment. These

parameters were calculated as followst

Ciloulatlona

Food Conversion Ratio (FCR) I This waa ealoulated from the following

relationship

TOR - Amount of food fed (o) ea dry waioht Total wet weight gain (g)

i’rotein efficiency ratio (PER)

PER * Total wat weight gain (□)Amount of Protain fad (g)

Spacific growth rata (SGR)

SGR - logaM2 - 109,11), X 100

whara • final naan weight of fiah

W1 ■ initial naan weight of fiah

t ■ time interval in days

Mean weight ■ Total waioht No, of fish

Feed Analysis

Ths crude protain content of tha formulated diet waa determined by

the micro Kjaldahl method (Rsrkham, 1942) tha fat content by soxhlet

extraction with petroleum ether. Ash content was determined by heating

a weighed sample of tha diet in a muff la furnace at 450°C for 12 hours.

The moisture content was determined by drying a weighed sample of ths

feed in an oven at 105°C for 24 hours.

Ths gross energy content of the diet was determined from proximate

analysis values by calculation using the factors 5.7kcal/g for protein,

9.5kcal/g for fat and 4.1kcal/g for nitrogan-frss extractives (NFE)

(Brody, 1945).

Feed Preparation for digestibility studies

During formulation of tha experimental diets, 0.5g in 100g diet, of

chromic oxide was included in each ration before palleting. Tha diets

and tha faacas of ths fish ware than analysed for chromic oxide oontent

by tha method of Furukawa and Taukahara (1966). Tha weights of tha

chromic oxide wars than used in determining the digsstibilitlas of tha

different experimental diets.

Collection of faeces

Faeces wars collected once a day during tha last weak of tha

experiment et 1.00pm, by siphoning the wster conteining faecal material

into a bucket. This was thmn vacuum filtered immediately in a Buchner -

flask fitted with Whatman paper (Dyka and Sutton, 1977). Prior to

collection of the faeces any faeces and debris of uneaten food was

removed in order to ensure that the faecal material collected was as

fresh and uncontaminated as possitts to ensure accuracy of reaults and

that no leaching of nutrients had taken place. After collection the

faeces were then dried in the oven at 100°C for 24 hours prior to

analysis of pooled samples for chromic oxide and protein to enable

protein digestibility determination.

Determination of chromic oxide in feed and faeces

About 200mg of the sample was accurately weighed and transferred

carefully to a dry 100ml Kjeldahl flaak. Into this was carefully added

5ml of concentrated nitric acid and the mixture was left to stand for a

short period. After this the flask was heated gently in a gas mantle

until a white precipitate was obtained (for about 20 minutes). The

flask was than allowed to cool before 3ml perchloric acid was added to

the digestion mixture. The flask was then re-heated until the green

colour chenged to yellow, orange or red. The flask was than allowed to

ooo1 down slightly before 50ml of distilled water was added. Then the

mixture was cooled to room temperature end made up to 100ml in a

volumetric flask with distilled water. The solution was then trans­

ferred to a colorimetric tube and the optical density was road at 350mu

against distilled water as blank. The chromic oxide content (X) was

calculated from the following relationship.

X ■ absorbency reading - 0.032 x 100weight of sample in mg/100g dryweight

The apparent digestibility was calculated aa follows

App. Olgaat. - 100 - (100 x * Cr-0- in feed x ft Pfgfin 10 ftlBIt)( % Cr'Oj in faaoas % Protein in feed )

and the dry matter digaatibility was calculatsd as follows

Dry matter Digest. - 100 - (100 x % Cr203 in fasces)

( % Cr203 in feed )

(Furukawa and Tsukahara 1966)

Carcass analysis of fish

Before the beginning of ths experiment and at ths and, six fish from

each tank were sacrificed and proximate analysis was performed on them

by the methods already stated.

The following parameters were then calculated from ths results of

the analysis.

Apparent Nat Protein Utilization

App. NPU - B - Bo x 10Q

where

B * Total body protein of test fish st and of trial Bo * Total body protein of fish at beginning of trial I ■ Protein intake on test diet.

If a zero protein diet was fad to ths fish during the experiment

then the following can also ba calculated.

Nat Protein Utilization

NPU I 100

whare

B ■ Total body nitrogen of test fish at and of trialBk - Total body nitrogen of fish fad zero protein dietI ■ Nitrogen intake on teat diet.

True Oigostibility (TO)

TD • I - (F - rk)x x 100

whore I » Nutrient intakaF ■ Faocal nutrientFk ■ metabolic faooal nutriont

Biologioal Value (BV)

m x 100TD

Statistical analyoool

Those wore performed by the method of Dunean multiple

RESULTS

The results of the proximate chemicsl analysis of ths plant

protein sources are presented in Table I, whilst Table II shows ths

proportions of protein supplied by ingredients in experimental dists.

Proximate analysis of formulatsd diets is in Table IV.

Of the three plant materials, soyabean has ths highest level of

crude protein (46.7$) followed by rapeseed (38.6$) and then sunflower

seeds (31.3$). There is less variation in ths lipid levels. The

sunflower seed meal has the highest value (2.8$) followed by soyabean

meal (2.2$) and then by the rapeseed meal (1.7$). All three of these

protein sources are 'meals' produced by mechanical and solvent lipid

extraction of the raw product followed by grinding.

The proximate analysis of the experimental diets show close

approximation to the formulated nutrient levels. Instead of the

30$ protein value formulated for each of the six diets there was

variation from 29.1$ in diet 2 to 32.5$ in diet 1 as shown in Table IV.

These variations are email and no more than expected. The mineral and

vitamin mix content are presented at the bottom of Table III.

The proximate analysis of the fish initially and at the end of the

experiment are shown in Table VII.

The proximate analysis of the faeces if shown in Table V. The

chromium oxide content of the diets is generally lower than the

formulated values. This may be due to some losses during mixing of

the ingredients. However the level in the faeces is much higher than

in the diet ae expected. But the level of protein in the faeces is

much lower then in the diet suggesting that muoh had been abeorbed into

the body for growth.

Diet Acceptance

The control diet, in which the protein souroe was herring meal, was

no re acceptable to the fiah than any of the other experimental diets

most especially during the first week of the experiment. This was

probably due to the fact that the fish had bean fed on a fishmeal based

commercial feed during the acclimation period and had become used to it

thus not readily accepting alternative materials. Furthermore, the

texture of the control diet was slightly softer. Soma of the

experimental diet% especially the ones containing sunflower seed meal,

were coarse and hard, and were not raedily ingested. For example,

diets 2, 5 and 6 wars often mouthed by the fiah and then spat out and

then mouthed again several times before ingestion, suggesting that they

may have been too hard for the fish. However, after being immersed in

the water for a few minutes they softened and ware more readily ingested.

One further observation concerning fiah fed diets containing

sunflower meal was that they produced danse faeces which could be seen

at the bottom of the tank. This may have been due to the high fibre

content of sunflower seed meal (Gohl 1975). This would have mada the

diets containing thia protein source leas digestible than the others.

The fish fed on diets containing rapesead maal and aoyabsan meal

produced leas apparent faeces than ths ones containing sunflower seed

meal but mora than tha ones fed fiehmaal.

Growth

The average specific growth rate (SGR) for each diet is presented

in Table VI. The increase in averege fiah weight throughout the

experiment is shown in figure 1. Both sets of data show highest

growth rates for the control diet (fishmeal). Statistical analyaia

shows that diets 3 and 4 have a significantly higher specifie growth

rats than diets 2, 5 and 6. The control diet gave significantly the

highest growth. There was no signifiosnt difference between the

specific growth retes produced by diets 3 and 4. Also there is no

significsnt difference between SGR produoed by diets 2, S and 6.

These results showed thst diets containing 5% fishmeal and 25J6 protein

from either rapsseed meal or soyabean meal produced better growth then

the purely plant protein diets (diets 5 and 6) or diet 2 containing %

fishmeal and 25% protein from sunflower meal,

mortality

The parcentsge of mortslity was generally low as shown in Table VI.

However the percentage mortality in fish fed diets 1 and 4 was much

higher than in the other diets for reasons which are not understood.

Body composition

The proximate carcass analyses of fish et the beginning and at tha

end of the experimental period are presented in Teble VII. The gross

body composition was not greatly altered during the experimental period.

However, there wes slight variation according to the dietary protein

source. The fish fed on diets containing sunflower seed meals (diets

2, 5 and 6) had lower levels of pro tain than those fed diets containing

either all fishmeal or 25£ protein from rapaeeads or soyabean but there

was no significant difference betwasn them. Only the fishmeal protein

fed fish had a significantly higher protein content than the others.

There was no significant difference between the moisture level in

the fish fad the different diets. The lipid level in fish fed the

control diet wes significantly higher than values for the other diete.

This was followed by diete 3 and 4, then diete 5, 6 and 2 rsepectively.

Tha body moisture and lipid level appeared to be slightly inversely

relsted ea has been noted in previous experiments (Kausch and Ballionousmano,

1976j Dabrowska and Wojno, 1977; Crayton and Beamish, 1977j Hurray

et al.. 1977; Ateck at al. 1979; Oauncey 1980).

Body ash was not much affected by dietary rsgieme ae has bean noted

with other fish species (Phillips et al. 1966, Cowey etji. 1974,

Elliot, 1976; Dabrowsks and litojno, 1977; Yu at al. 1977; Atack at al.

1979).

Food Conweraion ratio (FCR)

The values of the food conversion ratios are presented in Table VI.

The pattern of variation ia similar to that of mean weight and specific

growth rates i.e. diet 1 gave the best value followed by diets 3 and 4.

Thera are no significant differences in FCR values between diets 2, 5 and

6. However diet 2 had the lowest FCR followed by 5 and 6 respectively.

Protein efficiency ratio (PER)

The average protein efficiency ratio (PER) values are preaented in

Table VI. Fishmeal gave the best value followed by diets 3, 4 and 2

respectively.

Apparent Net-Protein Utilization

Since no zero protein diet was included in the experimental diets,

the true net-protein utilization was not calculated. Inetead the

apparent net protein utilization wae calculated from the carcass analysis

data presented in Table VII.

The fishmeal diet gave the highest value followed by diets 3, 2, 5,

4 and 6 in decreasing order.

Apparent Digestibility

The apparent protein digestibilities of the diets are presented in

Table VI. They were determined by analysis of faecal samples.

Diet 4 gave the highest value followed by diets 6, 1, 3, 5 and 2 in

decreasing order

TABLE III ? Composition of experimental dieta

Ingredianta Diat1 2 3 4 5 6

Herring meal 43.52 7.3 7.3 7.3Sunflower 80.4 24.1 24.1Rapeaaad 64.8 38.9 19.4Soyabean 51.3 15.4 30.8

Lipid derived from fiahmaal 4.5 0.8 0.8 0.8Lipid derived from plant

protein aourca 2.3 1.1 1.1 1.6 1.7Cod liver oil 0.5 4.2 4.2 4.2 5.0 5.0Corn oil 5.0 2.7 3.9 3.9 3.4 3.3

Mineral mix2 2 2 2 2 2 2Vitamin mix 1 1 1 1 1 1Binder 2 2 2 2 2 2Chromic oxide 0.5 0.5 0.5 0.5 0.5 0.5Starch 22.74 2.7 7.2 13.9 3.9 5.9Dextrin 22.74 2.7 7.2 13.9 3.9 6.0

Total 100 105.5 100.1 100 100.1 100

1 Mineral mix : - g/lOOg2 Vitamin mix s - g/lOOg3 Binder

1 Mineral Mix (g/lOQg)

MgS04 7H20 12.75g KCL 5,>0g, Nacl 6.0g,

CaHP04 2H20 72.78g FeSQ4 7H20 2.5g, ZuS04 7H20

CuS04 s h2o O.OSg, MuS04 4H20 0.25g, CoS04 7H20

C.I03 6H20 0.03g, CrCL3 6H20 0.01g

0.55g

0.05g

2 Vitamin aupplamant (g/lDOg)

Thiamine (B) 0.30g, Riboflavin (B2) 0.76g, Pyridoxin Bb

0.20, Panthothanic acid 2.00g, Inoaitol 7.10g

Biotin 0.10g, Folic acid O.OBg, Parci aminobanzoic acid 1.50g,

Choline 30.00g, Niacin (Nicotinic acid B3) 2.66g, Cyanocobalamin

(B12) 0.005g, Vitamin A (Retinol palmitate) 10,000 u, x - tocophanol

(E) 1,5g, Aacorbic acid (C) 10.Og Menadione (K) 0.2g, 0f

cholicalcitarol 1.0g.

3 Binder - Sodium Carboxymothylcalluloaa (high vlacoaity)

41

TABLE IV t Proximate analysis of Experimental diets

Component1 2

Oiat3 4 5 6

Moisture 1.3 1.4 1.6 1.6 1.7 1.5Crude Protein (%) 32.5 29.1 30.9 32.0 30.8 30.7Ether extract (%) 10.2 11.2 8.6 9.2 8.8 8.8Ash (%) 15.0 15.4 15.5 15.2 15.9 15.2NFE 41.0 42.9 43.4 42.0 42.8 43.8GE Kcal/g 6.4 6.2 6.9 7.1 7.4 6.5PjE ratio 50.8 47.0 44.8 45.1 41.6 47.2

GE t calculated on tha basis of

Protein 5.7 keal/gFat 9.5 keal/gNFE 4.1 keal/g

Broady, (1945) Bioanargatics and growthPublished by Reinnold, New York, U.S.A.

NFE t Nitrogen free extractives calculated as NFE dsrived fron fishmeal and dietary starch ♦ dietary dextrin

GE : Gross energy content

P:E : Protein to energy ratio in mg protein/kcal of GE

TABLE V i Proximate analysis of protein in faeces and chromic oxide in

Oiat

diets and faeces

^ ^r2°3% Cr203 % Protein

in diet in faeces in faeces

1 0.15* 0.56* 21.5*2 0,19* 0.27* 11.5?3 0.15* 0.45* 18.6*4 0.21? 0.89* 20.5*5 0.19* o .m J 15.25°6 0.20* 0.52* 13.7°

Figures in the aame column having the same auperacript are inaignifioantly different (P < 0.05)

43

TABLE VII : Gross body composition data

Diet Body composition wet weight)

Moisture Fat Protein Ash

F° 75.1 6.6 14.3 3.6

1 71.7® 9.5® 16.8® 4.3®

2 71.9® 5.9C 15.5® 4.3®

3 72.6® 7.5b 15.9® 4.2®

4 72.7* 7.7b 15.8® 4.1®

5 73.3® 6.4° 15.4® 4.2®

6 74.1® 6.1C 15.8® 3.9®

r° - Body composition of sample fish analysed at the beginning of the experiment.

Figures in each column having the same superscript ere insignificantly different. (P< 0.05)

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DISCUSSION

Tha crude protein levela of 31.1%, 38.6% and 48.7% for sunflower,

rapeseeds and soyabean meals respectively aa presented in Table I arm much

lower than the 68.9% obtained for fishmeal. Their crude protein levels,

however, are high enough for their uee as protein sources for the feeds of

Tilapia and Sarotherodon species to be considered.

The protein requirements of tilapia are dependent on many factors,

especially siz% and appear to lie between 29 and 38 per cent (Cruz and

Laudencia, 1977; Davies and Stickney, 1978) for fingerlings. As the

percentage protein in sunflower seed meal is only 31.1, it was not possible

to formulate a solely plant protein diet of 30% crude protein from it.

In order to compare it with the other plant protein sourcs% the fishmeal

was only partially substituted by the plant sources in diets 2, 3 and 4.

Only diets 5 and 6 were solely plant protein diets each formulated from

all three of the plant protein sources.

The crude protein content of the six diets, based on proximate

chemical analysis, varied from 29.1 - 32.5 per cent, as compared to the

computed value of approximately 30 per cent. Cruz and Laudencia (1978)

observed a wider variation of 29.6 - 36.6 per cent from the computed value

of 30 per cent in their experiment using fishmeal, rioe bran fine, copra

meal, soyabean meal, and mulberry leafmeal in the culture of tilapia.

These workers attributed the variation to lack of homogeneity of the

feedstuffs. Thus the variation in tha present experiment was ooneidered

acceptable.

Results of the acceptability trial showed that the fish had difficulty

in consuming some of the diets. Perhaps an improvement in formulation or

pelletisation of the feed might have enhanced their consumption. A

possible method of doing this would hsve been to make them softer by

raising the moisture content. Ptabays (1971) noted that one of the prime

considerations in preparing fish diets is acceptance together with the

whole array of its attendant physical and biological factors with which

it varies. He also noted that unless food is acceptable to fish, it is

of little value however well balanced it may be. fish may accept or

reject food according to whether it is coarsely or finely divided or

given dry or moist.

Swingle (1968) demonstrated thet there wee significant benefit to

feed conversion for catfish and carp if the feedstuffs were pelleted.

Allison et al. (1976) however observed no significant difference in net

yields and feed conversions when they cultured Tllapia eurea. More

research needs to bo dons with other feedstuffs and other tilepia species

before a general rula can be stated on what form of feed is the best to

use, and how a particular form of feed affect growth and development of

a given fish. Pelleted feeds are usually directly consumed by the fish

whereas the same ingredients fed in an unpelleted form under pond

conditions also act as a fertilizer increasing natural food production.

The form of the feed thus depends on whether the grsetest benefits are

obtained by direct consumption or indirect fertilization. In intensive

culture situations with a through-flow of water pelleted feeds are

obviously required.

Growth

The everage specific growth rates obtained ware somewhat similar to

values obtained with mirror carp (Atack et al. 1978) in an experiment

employing herring fishmeal, soyabean meal and Splrulina as the protein

sources with a 30% dietary protein level. The averege specific growth

ratea in the above experiment were 2.3%, 1.24% and 1.2% per day

reepectively for the three protein sources.

As already indicated diets containing eolely fishmeal or partial

substitution of it (diote 1, 2, 3 and 4) generally produoad higher growth

rates than those containing only plant proteins as in diets S and 6.

47

This observation is supported by Lloyd et al. (1578) who stated thet the

essentiel amino acid content of animel protein is generelly better then

that of plant proteins because it approximates to the amino acid profiles

of the enimal itself. This might account for the higher specific growth

rates obtainable with the high fishmeal diets. However, diets 2 and 3 and

4, having the same percentage protein supplied by fishmeal, produced

varying specific growth rotes, which must have depended directly on the

plant protein source. Among these three, diets 2 and 4 produced poorer

specific growth retes than diet 3. This varietion must be due to the

neture of sunflower, soyabean meal and rapeseed meal. Diet 4, which

contained meinly soyabean produced lower growth rates then rapeseed

possibly because soyabean is deficient in the essential amino acids

methionine and lysine (see Table VIII).

As for diet 2 which was mainly sunflower seed meal in composition,

poor specific growth rate can be attributed mainly to the high fibre

content ' (Gohl 1975). Also the amino acid balance may be partly

responsible.

As indicated in Table VIII diets 5 and 6 would have emino acid

profiles not thet dissimilar to fishmeal, yet they produced the poorest

specific growth rstas. This is probably due to the absence of animal

proteins in them.

These obeervetions thus confirm thet growth depends on quality as

well ss quentity. To produce maximum growth it would appear that there

is a need to strike an optimum balance between the plant and animal

portions of the diet. However it must be realised that even though

chemioal analysis shows an amino acid to be praaant, it doss not

neceesarily follow that it la biologically available. Dora knowledge

is thus required on the digestive phyeiology to determine the best food

snd optimum feeding rates snd times.

Food Conversion ratio (FCR)

As shown in Tabls VI, the fishmeal (control diet) gave the best food

conversion as expected. This was followed closely by diet 3, while diets

2, 5 end 6 gave similar and poorer conversions. Atack at el. (1979) re­

ported food conversion of 2.50 when the mirror carp (Cyprinus caroio) was

fed with Soirulina. This value is poorer than 1.6 recorded for diet 3

but similar to 2.2 - 2.4 recorded for the pure plant protein sources in

diets 5 and 6. A comparison of the food conversion ratio for diets 1

and 3 suggests that rapsseed meal can successfully replace fishmeal at the 25£

protein substitution level. The same thing cannot however be said of the

soyabean and the sunflower seed meals.

The relatively low food conversion ratio obtained for the substitution

of fishmeal by soyabean at 25£ protein level may be partially attributed

to non availability of the amino acids it contains.

As Ll-oyd et al (1978)stated, soyabean can contain a trypsin inhibitor

which inactivates trypsin reducing protain digestibility. The soyabean

meal used in the current experiment appears not to be affected by trypsin

inhibitor as diet 4 shows the highest protein digestibility (Tabls VI).

Diet 2 which is fishmeal substitution by sunflower at 25£ protain level

also had a poor FCR probably due to its high fibre content which may have

resulted in poor absorption. Diets 5 and 6 had poor FCR probably because

fishmeal contains amino acids that are more available than those present

in the plant proteins.

The food conversion ratios in the present study are poorer than those

obtained by Atack at al. (1979) for bacterial meal (1.14), casein (high)

(1.39), herring meal (1.42) and yeast meal (1.55) in an exparimant using

carp. However the values are better than those for algal meal (2.50)

and soyabean meal (2.86) at identical 30£ protain level.

Amino acid profiles and digestibility data for the oilseed meals

would indicate a higher degree of utilisation and better food convereion

retioe than obtained in the current experiment. It is possible that the

the processing of these meals wee sufficiently hersh es to render some

of the essential amino acids, particularly methionine and lysine,

unavailable.

Protein efficiency ratio (PER)

The value of protein efficiency ratio reported in the present work

for diet 3 is very similar to the values reported by Soeder (i960) for

Spirullna (1.80). Scenedesmus (1.85) and Coelastrum (1.85) when he fed

tilapia with test diets. However the PER of about 1.4 reported here

for the pure plant protein sources of diets 5 and 6 is slightly higher

than that for Spirulina (1.15) and soyabean (1.35) reported for carp by

Atack et el. (1979).

Iilu ard Jen (1977), using Tilapia aurea, obtained a PER of 3.45 for

casein. This value is much higher than the value for the fishmeal in

the present work. His value of 2.23 for soyabean is also higher than

that for diet 4 (mainly soyabean) in the present work. The PER for

peanut cake (1.75) and yeast (1.13) are generally lower than the values

obtained in the present work. As already stated in the discussion of the

food conversion ratios, the poor protein efficiency ratios for diets 2, 4,

5 and 6 may be due to harsh processing of the oilseed meals, the high

fibre content of sunflower eaad meals and some essential amino acid

deficiencies.

It can thus be concluded that rapeseed meal appears to be the most

promising of the three oileeed meal protein sources investigated.

Apparent Net Protein Utilisation

The pattern of variation here was similar to that of food conversion

ratio and the protein efficiency ratio. The causes can also be

attributed to the nature of soyabean and sunflower as already stated.

Apparent Dloestlbllity

The apparent protein digestibilities as shown in Table VI are all

high. flenn (1967) recorded a lower digestibility value of 53% during

balance tests when feeding Tilapia melanopleura with the algae

Soirodella oolvrrhiza and Elodea Canadensis.

Shcherbina (1964) determined the digestibility of protein from sun­

flower and cottonseed oil meals for carp as 76.8% and 73.7% respectively,

and in another study Shcherbina and Sorvacher (1967) obtained

digestibilities of 74.5% and 76.2% for sunflower and cotton seed

respectively. These values are very similar to those of diets 2 and 5

containing sunflower in the present work. Though diet 6 also contains

sunflower, its digestibility is higher possibly due to the higher

digestibility of the soyabean it contains.

The values in the present work are however lower than determinations

made for the common carp (Cvorinus carpio) where the digestibility of the

fishmeal was 89%, the alga Zygnama 92% and flougeh'a 95% (Singh & Bhanot,

1970).

In the present work, diets 4 and 6, which have the highest proportion

of soyabean, have the highest digestibilities. This suggests that soya­

bean is more digestible than rapeseed maal and sunflower meal, and avan

fishmeal. On the other hand, diets 2 and 5 which have the highest

proportion of sunflower seed sisal have the lowest digestibilities. This

is probably dua to the high NFE and hence fibre content of the sunflower

seed meals.

The digestibility of rapaseed meal is close to that of the fishmeal

as is indicated by the similarity of the value for diet 3, which has the

highest proportion of rapesesd meal, with thé fishmeal control.

However, there was not such variation in the digestibilities of the

6 diets

CONCLUSIONS

Investigations to find more economic fish feeds than fishmeal will

probably continue because of the high cost of fishmeal which is by far

the most widely used protein source of animal origin in fish feeds.

The factors responsible for the high cost are; the expansion of the

aquaculture industry in virtually all the countries of the world which

makes the demand for the fishmeal rise every year; another factor is the

sea fishing regulations and quotas imposed by the United Nations which

limit the activities of certain fishing companies and thus reduce the

supply of the commodity. Also the competition for fishmeal as food

for other domestic animels coupled with the growing interest all over

ths world in the use of all fishery resources as human food have made

the cost prohibitive.

In order to make more economical use of proteins in fish feeds,

which would effect significant reduction in total feed cost, researchers

have turned their attention to many potential fishmeal replacers. One

important maans that has been thought of, replacing fishmeal, is the use

of a new generation of novel feed ingredients such ae t

a) Single cell protein (SCP, 'Pruteen' ICI bacterial protein, yeasts, algae)

b) Plilk replacers (a.g. animal and plant protein concentrates)

c) Whole food organisms (e.g. terrestrial/aquatic worms silk worms, pupae, krill)

d) Animal and food processing waates.

The cold water carnivorous fishes like the salmonids have a high

dietary requirement for protein and are likely to benefit in the use of

milk replacars, whole food organisms and animal processing wastea, in

which a lot of research is currently being undertaken. Ae for

herbivorous or omnivorous fishes like tilapia the uee of some single

call protein and food prooessing wastes hss been investigated. Among

theaa the algae and oertaln food processing waste produots, like spent

52

beers and coffee pulp, have been identified as possible fishmeal

repl8cers.

The second means of replacing fishmeal is the use of existing feed

ingredients but maximising their utilization. In the culture of

tilapia the existing feed ingredients are mainly plant proteins both

aquatic and terrestrial, and a lot of research has been conducted on-

them. For in&ance, the cereals have been evaluated and found to be low

in protein level and thus are normally incorporated at relatively low

dietary inclusion levels (5 - 10%) by weight for individual secondary

protein sources depending on the food stuff (Tacon, 1981). In contrast,

the oil seeds generally have higher protein levels but research performed

on them to date is scanty, hence their selection for the present study.

The throe oil seeds, sunflower, rapeseed and soyabean can bs grown

in tropical and sub-tropical regions (Godin and Spensley 1971) and hence

would be economical fishmeal replacers if they are accepted by tilapia.

Of the three plant protein sources, rapeseed meal had the best food con­

version, protein efficiency ratio, and specific growth rate. This was

followed by soyabean while the sunflower was the poorest due probably to

its high fibre content. The sunflower used in this trial was unusually

poor. It had a very low protein content and may not reflect sunflower

seed meal in general.

Though the fiahmsal gave higher values for the parameters already

enumerated, the plant sources gave fairly high values, especially the

rapaseeda which, in some eases, ranked equal with the fishmeal. Thus

the rapeseed meal would appear to be a potential partial fishmeal rsplacar.

Plore work is however required to improve the utilization of the

three plant materials. In the past, processing of such ingredients as

complete soyabeans or other oil-bearing seeds or cereals for animal

feeding, consisted of grinding, crushing or flaking.

Now, with tte aid of various heat-proceaaing tschniquas, it is

possible to grestly enhance the nutritionel characteristics and

consequent feed value of feeding stuffs such as full-fat oil seeds

and cereals, which otherwise may have only small feed value to the

animal. As previously mentioned, these heat-processing techniques

have been used in eliminating the trypsin inhibitor in soyabean,

and inactivating myrosinase which in turn reduces the growth inhibitor

(glucosinolate) present in rapeseed.

Another means of maximizing the utilization of the feed ingredient

is through genetic selection. This is very relevant in the case of

rapeseed which consists of different strains, many of which may possess

a high level of toxic substances. The rapeseed strain used in this

study gave good results, probably due to its low level of toxic

substances. By means of genetic selection the unfavourably high

level of toxicity in oilseeds can be decreased. More work needs to

be done in this ares for more plant protein used in fish feeds. Though

improvement of growth of fish through amino acid supplementation is at

present less than rewarding, and the results contradictory, this

should be tried as a means of improving the utilization of the plant

sources in the present study.

Another area where more work needs to be dons is the evaluation

of these oilseeds under pond conditions which may vary significantly

from those of a laboratory aquarium.

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a

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This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with its author and that no quotation from the thesis and no information derived from it may be published without the author’s prior written .consent.