138

Eapen Jacob, 2013. Studies on the captive breeding and

reproductive biology of two indigenous ornamental

fishes of the Western Ghats. Ph. D Thesis, Mahatma

Gandhi University, Kottayam, India

CHAPTER 2

REPRODUCTIVE BIOLOGY OF

PRISTOLEPIS MARGINATA JERDON,

1849

2.1 INTRODUCTION

In order to obtain a comprehensive insight into the biology, population

dynamics, applying monitoring, conservation and management programs of a particular

species, its reproductive potentials should be investigated. Different reproductive

parameters and indices such as number of produced eggs (fecundity), ova diameter,

condition factor, stages of maturity, sex ratio, gonado-somatic index, modified gonado-

somatic index (MGSI) have been used to determine reproductive status and spawning

season of different fish species (Nikolsky, 1963; Biswas,1993, Dobriyal et l. 1999,

Esmaeili 2009)

139

A complete knowledge of the reproductive system and the reproductive biology

of fishes are essential to understand the reproductive strategy of any given species.

Quite some work has been done on the fish reproductive system namely the gonads and

their development. The notable of these early works are those of Yamamoto (1956 a),

Yamamoto and Yamazaki (1961). The literature on the reproductive organs and

reproduction was reviewed by Raven (1961), Hoar (1969), Nagahama (1983), West

(1990) and Jalabert (2005). Recent works on the reproductive biology of the Western

Ghts fishes involve those of Dasgupta (2002), Kurian and Inasu (2002), Goswami and

Dasgupta (2004), Mercy et l (2004) and Divipala (2008). There has been little work

carried out on the reproductive biology of fishes of the family Nandidae. Pal et al (2003)

reported the artificial spawning of Nandus nandus. The only work on another species,

Pristolepis malabaricus was that of Sherly (1983). Therefore, an in depth study on the

reproductive biology of Pristolepis marginata was taken up in order to have baseline

information for the captive breeding programme of the species.

2.2 MATERIALS AND METHODS

Specimens of P. marginata Jerdon for the reproductive biology studies were

procured directly from its natural habitats by means of caste net operations. The F1

generation individuals produced in the hatchery were also used for the studies. The

collected specimens from different locations in Bharathapuzha river, approximately 150

km away from the College of Fisheries, Cochin, where the laboratory and hatchery

facilities were established, were transported in polythene bags where water and medical

oxygen were kept at a ratio of 1: 5. They were acclimatized to captive conditions in the

140

hatchery by gradual exchange of water. Fishes were kept in well oxygenated bio-filter

attached glass aquaria as well as in cement cisterns. pH ranged from 7 to 7.5. Fishes

were maintained under ambient temperature conditions (27-29 0C).

2.2.1 Quantification of maturity stages

A total of 160 female fishes (75- 85 mm ) were used for the study of breeding

biology. After measuring the length and weight of the individual specimen (Total length,

Standard Length and weight) of the specimen the body was cut opened and the gonads

were cleared of peritoneal covering and fat bodies if any. The ovaries were fixed in 5 %

formalin and detailed investigations on quantification of ovary were carried out.

Quantification is based on external evaluation of the gonad (Qasim, 1973).

Macroscopic quantification characters used are:

1. Color and shape of the gonad

2. Space it occupies inside the body cavity

3. Texture of the gonad

4. Size of ova and blood supply

A series of scales of ripeness have been worked out for each group of fishes for

delimiting the different stages of the sexual cycle, based on a universal scale of six

stages proposed by Nikolsky (1963), mainly for temperate species. In the present study,

a modified five - stage key based on the reproductive strategy of tropical fishes was

used. The most common five point maturity assessment method, ideal for most tropical

fishes are as follows. Stage I- Immature virgins; stage II- maturing virgin; stage III-

mature and ripening; stage IV- ripe and stage V- spent. In order to assess the oocyte

141

maturity, a piece of ovary from a representative freshly collected specimen was gently

teased on a clean glass slide along with a drop of one percent formalin, the diameter of

the egg was measured and oocyte frequency profile was constructed.

2.2.2 Size at first maturity

Size at first maturity was computed separately for males and females. A total of 160

fishes were used for computing the Size at first maturity. It is the length at which 50% of

the fish population is regarded to have attained maturity (Kagwade, 1968).

The total lengths of all fishes collected for the study were grouped according to

different length groups. The percentage occurrence of four stages (ripening, ripe, spent

and partially spent) for females was found out. By plotting the percentage occurrence of

mature fish against respective length classes (10 mm), maturation curve is obtained.

From this maturation curve, the length at which 50 % of the fishes become mature can

be demarcated.

2.2.3 Spawning frequency

Ovaries belonging to all the stages of maturity were preserved in 5 % formalin

for ova diameter measurements. The ova diameter measurements were done on a

monocular microscope with 10 X magnification, after standardizing the calibration of

the ocular micrometer using a stage micrometer. A mixed subsample was taken from

different parts of the ovary to eliminate any error due to differential distribution of ova

stocks in different parts of the ovary. The diameters so obtained are then represented

142

graphically. The spawning frequency of the fish is obtained by plotting the percentage

frequency against different ova diameter classes (ova stocks).

Ova diameter measurements were also taken from ovaries at different stages of

maturity to study the progression and development of the ova following the method

adopted by Clarke (1934), Hickling and Rutenberg (1936), De Jong (1939), Prabhu

(1956) and Nair and Nair (1983).

2.2.4 Fecundity

Ripe ovaries of 16 fishes of size range 66 to 104 mm SL were used for the

present study. During the initial quantification process itself those ovaries (stage V)

were preserved in 5 % formalin. Later these samples were weighed after wiping with a

blotting paper and length and width of each lobe of the ovary was measured. Average of

the lengths of the two lobes has been taken as the length of the ovary. From a weighed

ovary, a minimum of 4 samples were taken at random. Weight of the sub samples

ranged between 0.1888 to 0.2999 g. Weighed sub samples were then kept in Gilson’s

fluid (Based on modified Simpson, 1959) with appropriate labels showing standard

length, ovary weight, sub sample weight etc. It is then shaken vigorously and left for 24

hours. Gilson’ fluid hardened the eggs and helped to liberate them by breaking the

ovarian tissue. The samples can be left for several months without any disadvantage.

143

Table 2.1 Gilson’s Fluid Composition

Component Quantity

60 % alcohol : 100ml

80 % Nitric acid : 15 ml

Saturated formalin : 20 ml

Water : 880 ml

Glacial acetic acid : 18 ml

Counting

Fecundity was calculated by gravimetric sub sampling method. Since fecundity is

defined as the total number of mature or maturing eggs present in a ripe ovary, all the

yolked eggs were considered for the counts (Hickling and Rutenberg (1936). Sub

samples kept in Gison’s fluid were counted manually by taking in a watch glass.

Average number of eggs was calculated for the sub samples. Then on the basis of the

average count and average weight of the sub samples as well as the weight of the ovary,

the total or absolute or individual fecundity was computed using the formula.

Weight of the ovary X Average number of eggs per sub sample

Fecundity = ------------------------------------------------------------------------------

Average weight of the sub sample

144

Relative Fecundity

Absolute fecundity calculated was expressed in terms of unit body weight, unit body

length, unit ovary weight and unit ovary length.

Fecundity - Length and Fecundity - Weight relationships

A logarithmic transformation of absolute fecundity to body length (SL) and

ovary length (OL) and absolute fecundity to body weight (W) and ovary weight (OW)

can be expressed as follows,

1. Log F = Log a + b log L

2. Log F = Log a + b log OL

3. Log F = Log a + b log W

4. Log F = Log a + b log OW

These lines can be fitted by the method of least squares, using standard statistical

procedures for subsequent analysis.

2.2.5 Reproductive strategy

The different reproductive strategies of a fish species can be explained based on

the studies on different reproductive biological aspects like fecundity, ova diameter

frequency studies. Study on captive breeding and breeding behavioural patterns also

give picture of different reproductive strategies of a species (Balon, 1984).

145

2.3 RESULTS

2.3.1 Classification of the maturity stages

Female maturity stages

(1) Stage I – Immature virgins

Young individuals that have not yet spawned. Differentiation of the gonads has

just taken place. Ovaries in this stage are very small, triangular and translucent.

They are usually translucent; pinkish occupying less the one fourth of the body

cavity. Ova are not visible to the naked eye.

(2) Stage II – Maturing Virgin

Oocytes yet to develop (virgin). Ova were not visible to the naked eye; only

transparent immature stock was present. In maturing virgins ovaries were

usually pinkish, translucent occupying about one third of the body cavity. The

right lobe was slightly larger than the left lobe. Ova were still microscopic,

irregular in shape with large nucleus and slight yolk deposition. Ova size was

up to 350 µ, the majority of the ova being in the 132 to 264 µ.

(3) Stage III : Mature and ripening

Ovary was usually yellow or pale yellow occupying half to less than three

fourth of the body cavity (process of vitellogenesis). Ovary usually turgid and

ovarian wall transparent and ova were quite visible to the naked eye. Ovary

increases in weight rapidly. The majority of the ova range between 396 - 595 µ,

the maximum size being around 650 µ.

146

(4) Stage IV : Ripening II

Ovary was yellow or pale yellow in colour, occupying ¾ th

or more of the body

cavity. The right lobe of the ovary being visible through the extremely thin

ovarian wall. The ovary was turgid but the ripe ova yet to run out when pressure

was applied. (Vitellogenesis over, yet to ovulate). The ova stocks ranged

between 6oo and 1450 µ, majority of ova being in the size range from 1100 to

1160 µ.

(5) Stage V : Ripe

Ovary was yellowish in colour. Ovarian wall was extremely thin and ova quite

obvious. Occupied more than ¾ th

or whole of the body cavity. Ovary was very

turgid. Ovulation was complete. Slight pressure on the abdomen resulted in the

extrusion of ripe ova. The size range of mature ova stock ranged from 990 to

1355 µ, the mode being in the size range 1320 to 1355 µ. Maximum size of the

ova was around 1800 µ.

(6) Stage VI: Partially spent

Ovary was slightly flaccid, pale yellowish in hue not as stout as ripe ovaries but

still retaining a large number of ripe ova (100 to 1400 µ) after one or two

batches of them have been spawned. Ovaries may contain remnants of

disintegrating ripe ova (residual or atretic ova).

2.3.2 Size at first maturity

The length (Standard length, SL) at first maturity was determined by analyzing

the data relevant to all mature fishes (Stage II and above) were examined. The

147

percentage occurrence of the four stages (ripening I and II, ripe and partially spent) for

females and three stages (ripening, ripe and spent) for males were plotted against length

classes for both males and females.

While the first mature females appeared in 30-40 mm length group (15 %), the

first mature males appeared only in the length class 50-60 mm (17 %). 58 % of the

females matured before 50 mm where as 56 % of the males matured only on reaching a

standard length of 70 mm. All female fish were mature reaching a length of 90 mm SL

and all male fish on reaching a length of 120 mm SL. The size at first maturity for

females is 54 mm SL (50-60 mm length group) and 72 mm (SL) for males (70-80 mm

length group).

2.3.3 Distribution of ova in the ovary

Ova diameter measurements were taken from anterior, middle and posterior

regions of the ovary for understanding the pattern of oocyte distribution.

Growth of ova in the ovary

To eliminate the possibilities of slight differences in ova stock distribution

between the regions of the ovary, mixed sub samples were taken for the ova diameter

measurements to study the growth of ova in the ovary.

Stage I is characterized by virgin stock alone. 97.2 % of the ova are represented in the

diameter class 33-100 µ and only 2.8 % is represented above 100 µ but usually this

stock falls below 150 µ. The ova stock constituting the virgin stock biomass is generally

148

not yolked. The eggs were transparent each with a large nucleus and generally shapeless

(Plate 2.2 fig.1).

In the second stage, maximum size of the ova is 400 µ. Yolk deposition is found to

occur in ova above 150 m (Plate 2.2 fig.2). During stage III, there are two modes, one at

100-2000 µ and the other at 300-500 µ diameter class. In this stage leading model is

positioned at 300-500 µ constituting about 35 % of the total ova stocks. 65 % is

constituted by the immature stock (Plate 2.2 fig.3).

IV stage is characterized by the presence of two modes. They are positioned at ova

diameter classes 300-400 µ, 600-700 µ and the leading mode is positioned at 600-700 µ

constituting about 58 % of the total ova stocks (Plate 2.2 fig.4).

V stage is characterized by maximum no of ripe eggs. Leading mode (ripe stock) is

positioned at 900-1600 µ. Maximum size of the ova present is in this stage is 1782 µ. In

the secondary mode ripening stock is seen in diameter class 500-900 µ. The immature

stocks are presented as 2 distinct modes at diameter classes 100-200 µ and 300-500 µ

respectively. Ripe stock constitutes 70 % of the total ova stocks constitutes 20 % of the

total ova stocks. Immature stocks form only 10 % (Plate 2.2 fig.5).

Stage IV is characterised by the backward shift of the leading mode due to the release of

fraction of oocytes at the posterior end of the ovary. Ripe stock constitutes about 50 %

of the total ova stocks. The percentage occurrence of ova diameter-class of ripening

stock has further strengthened occupying about 30 % of the total ova stocks. The fall in

149

the ripe stock from the ripe ovary to the partially spent ovary that does not undergo

atresia (Plate 2.2 fig.6).

Table 2.2

Ova dia.

class

Percentage frequency of different maturity stages

I II II IV V VI

0-100 97.2 48 29 11 4.02 10

100-200 2.8 43.5 25.3 6.2 4 8

200-300 8.3 10.5 3.4 1.5 2.5

300-400 0.2 18.32 2.5 2.01 2.01

400-500 13.2 0.67 0.4 1.2

500-600 2.1 3.25 4.5 4.5

600-700 1.23 13.5 8.2 12.5

700-800 1.5 5.45 9.3

800-900 0.59 1.2 1.17

900-1000 6.2 3 8

1000-1100 12.5 7.5 16.5

1100-1200 19.5 15.8 10.5

1200-1300 15 14.8 7.5

1300-1400 4.2 14.6 2.1

1400-1500 0.25 9.5 2.5

1500-1600 2.07 0.5

1600-1700 1.7 0.3

1700-1800 1.05 1.0

150

The process of maturation of the ripening and maturing stocks occur fast because

these batches of eggs have undergone half the process of maturation and hence only take

half the time taken by the immature stock to attain full maturity. These newly ripe ova

are extruded during the subsequent spawning processes, which occur with a very short

period thus the same individual spawning more than once during a year. Captive studies

have also shown that P. marginata is a protracted spawner, spawning in 3 or 4 times a

year. Maturation and spawning of the fish in captivity are highly influenced by

exogenous diet given as well as the ambient temperature conditions.

2.3.4 Fecundity

Results of the fecundity counts are given in Table 2.3. Absolute fecundity ranged

from 1102 to 4965 in fishes of sizes range 66-104 mm SL. The relative fecundity values

ranged from 166 to 517 per cm body length and 51 to 150 per g body wt. Relative

fecundity values also ranged from 622 to 2089 per cm ovary length and 760 to 1365 per

g ovary wt.

The relationship between fecundity and a) SL, b) wt of fish, c) length of ovary and d) wt

of ovary were found out and are represented in table 2.3 and illustrated in Plate 2.1 Fig.

1,2,3,4.

151

Table 2.3 Absolute fecundity observed in Pristolepis marginata

Sl.No. Standard

length

(mm)

Body

weight

(gm)

Ovary

weight

(mg)

GSI Fecundity

1 78 19.464 2.058 10.57337 2810

2 66 13.15 1.45 11.02662 1102

3 93 39.009 2.68 6.870209 3061

4 93 29.3 3.92 13.37884 4388

5 84 23.95 2.27 9.478079 2822

6 96 38 4.462 11.74211 4965

7 92 37.56 5.02 13.36528 4271

8 104 34 3.46 10.17647 4344

9 84 27.6 3.387 12.27174 3558

10 80 20.29 2.02 9.955643 1957

11 64 12.43 1.6 12.87208 1276

12 87 33.2 1.8 5.421687 1702

13 71 17.18 1.44 8.381839 1320

14 68 15 1.2 8 1300

15 61 13.65 1.75 12.82051 1301

16 80 26 2.12 8.153846 2000

152

Table 2.4 Relative fecundity observed in Pristolepis marginata

Sl. No Total

fecundity

Fecundity(per

cm body length)

Fecundity (per

gram body

weight)

Fecundity (per

mg ovary

weight)

1 2810 360.2564 144.3691 1365.4033

2 1102 166.9697 83.80228 760

3 3061 329.1398 78.46907 1142.1642

4 4388 471.828 149.7611 1119.3878

5 2822 335.9524 117.8288 1243.1718

6 4965 517.1875 130.6579 1112.7297

7 4271 464.2391 113.7114 850.79681

8 4344 417.6923 127.7647 1255.4913

9 3558 423.5714 128.913 1050.4872

10 1957 244.625 96.45145 968.81188

11 1276 199.375 102.6549 797.5

12 1702 195.6322 51.26506 945.55556

13 1320 185.9155 76.83353 916.66667

14 1300 191.1765 86.66667 1083.3333

15 1301 213.2787 95.31136 743.42857

16 2000 250 76.92308 943.39623

153

Table 2.5 Relationship of fecundity with different parameters

Sl.

No. Variant (x)

Constant

(a)

Regression

coefficient (b)

Correlation

coefficient (R)

1 Standard length

(SL) 0.6977 2.9486 0.7996

2 Body weight (g) 1.8733 1.093 0.7058

3 Ovary weight (mg) 2.8256 1.8299 0.2792

4 Ovary length 2.9496 1.1415 0.8922

2.3.5 Ova diameter studies

Ova diameter measurements were taken from anterior, middle and posterior

regions of the ovary for understanding the pattern of distribution of ova in the different

regions of the ovary as well as to eliminate the possible differences in occurrences of

ova in the ovary.

The distribution of ova stocks in the anterior, middle and posterior regions of a

ripe ovary are presented in table 2.2. It is evident that the gross picture of the ova stock

distribution from the three regions remains almost the same except for the slight

variations in the percentage composition of the mode. However, the ripe mode shifts

slightly in the posterior region (1300-1400 µ) indicating the presence of increased

number of larger ova in this region as compared to the anterior and middle regions. It

was also noted that ova above 200 µ in diameter are yolked generally. Fall in the ripe

stock from the ripe ovary to the partially spent ovary that does not undergo atresia

clearly points to the ‘batch’ or ‘functional’ spawning habit of P. marginata. Secondary

154

or ripening mode assumes greater importance in partially spent and spent recovering

ovaries which help in the recovery of the ovary to the ripe condition in a short period

leading to the same individual spawning again during the protracted spawning season of

the species.

Spawning Frequency

Ova diameter frequency studies have been carried out and they are illustrated in

the Plate 2.2. It is apparent from the figures that there are three batches of eggs

representing the ripe, ripening and immature stocks. Ripe stock is having a sharp mode

quite distinctly separated from the preceding batches. Ripe stock is destined to spawn

immediately. Immature ripening stock and immature stock are not as separated from

each other as the ripe stock. As the ripe stock of eggs is eliminated by spawning, the

batches represented by the ripening and immature stock undergo rapid maturation to

replace the ripe and ripening stocks respectively. Simultaneously a new stock of

immature stock also gets ready for the next breeding season.

2.3.6 Gonadosomatic index (GSI)

In the present study the highest GSI value recorded was 13.37 in the case of a

female fish of standard length of 9.3 cm and body weight of 29.3 g. The least 6.87 was

met with standard length of 9.3 cm and body weight of 39 g.

155

2.3.7 Reproductive strategy

Studies on different aspects of reproductive biology such as fecundity, ova

diameter analysis and gonosomatic index revealed that the candidate fish species P.

marginata is an asynchronous spawner i.e., a continuous development and release of

gametes in the gonads are evident. The fish showed affinity towards a pebbly substratum

or the presence of stones stimulated the fish to start the spawning activities. So the fish

could be included in the group of lithophils. The fish is also found to be nest builder and

highly territorial.

In general, P. marginata is an iteroparous species, i.e., they spawn more than

once during their lives and gonochoristic, i.e.,their sexes are separate and exhibit

external fertilization with parental care. A summary of reproductive strategies shown by

P. marginata is shown in table 2.6. The fish possessed an asynchronous type ovary i.e.,

oocytes of all stages of development are present without dominant populations.

The species could be categorized as a batch spawner i.e., eggs are recruited and

ovulated from the population of yolked oocytes in several batches over a protracted

period during each spawning season.

156

Table 2.6 Reproductive strategies of Pristolepis marginata

Sl.

No.

Component of breeding

system Reproductive strategy

1 Number of breeding

opportunities

Iteroparous (Multiple breeding

season)

2 Type of spawning Batch spawner

3 Mating system

Promiscuous (both sexes with

multiple partners during breeding

season)

4 Gender system Gonochoristic

5 Secondary sexual

characteristics Evident only during ripe stage

6 Spawning site preparation Nest builder

7 Place of fertilization External

8 Embryonic development Oviparity

9 Parental care Strong Parental Care

10 Spawning substratum Lithophil

Reproductive guild (Balon

1975)

Ecological classification: Guarders

Ethological classification: Nest

spawners

Morphotype : Lithophils.

157

2.4 DISCUSSION

When life history traits are utilized for evolving breeding protocols, it is essential

to monitor such characteristics among wild stocks so that such information can be used

for both commercial and conservation applications (Ponniah and Lal, 2000). A clear

understanding of reproductive biology of fishes is of vital importance not only for

successful natural fishery management but also for planning aquaculture strategies

(Bindu, 2006). Studies on the size at first maturity, fecundity, spawning season and

spawning frequency meant for the determination of breeding cycles with regard to

population are essentially meant for elucidating both short and long term variations in

the production of the broods which are finally recruited to the population as exploited

stocks (Begenal, 1966; Joshi and Khanna, 1980). Under captive conditions size at first

maturity, spawning frequency and spawning season shows a slightly different picture, as

these physiological parameters are highly dependent on the external diet and ambient

conditions provided. Hitherto, no such study has been reported on biology of the

common catopra, Pristolepis marginata. Hence in the present study an attempt was

made to understand different reproductive biological features, especially in captive

conditions, for the purpose to disclose the secrets behind its real spawning acts to

produce them in big numbers, to utilize in trade and at the same time save the species

from extinction threats. It is well known that within a species and among populations

surviving at different geographic locations, there occur major variations in life history

patterns. Such variations in reproduction, growth, and life history fitness traits are of

158

crucial significance for assessing the long term variability of the fish species (Ponniah

and Lal, 2000).

2.4.1 Size at First Maturity

In the present study, the size at first maturity of P. marginata is found to be

around 54 mm SL (50-60 mm) for females and 72 mm SL (70-80mm) for males. The

males mature only after reaching a much larger size. The largest female obtained during

the present study was 10.4 cm SL and males above this size were very common. The

largest male obtained being 15.5 cm SL. This is a kind of protective adaptation. Captive

studies have shown that male of the species showed that this species is a guarder and

builds nest with pebbles. The male alone is involved in this act of nest building and it

exhibits aggressiveness and strong territoriality when it is sexually mature

Ridley (1978) has classified male caring fishes into two types of mating systems, first,

those in which male remains with the eggs (male site-attached with or without

territoriality), and second in which male carries the eggs with him. Pristolepis

marginata can be included in the first group in which the males remain with the eggs

(site attached) with territoriality (Anna Mercy et al, 2003). The present study indicated

that as the male remained with the eggs until the larvae become free swimming.

Territoriality is to improve the probability of an individual offspring‘s survival to ensure

reproductive success. In egg laying fishes in which the males are territorial during the

breeding season, the males are often larger than the females (as in salmon). This is

usually the case when the male protects the offspring, so that larger size is a protective

adaptation (Nikolsky, 1963). However, in most fishes with sexual differences in size, it

159

is the female that is larger or at least achieves a larger size. This has also been suggested

by Keenleyside (1991). Size at first maturity in Etroplus suratensis (guarder, lithophil)

was found to be 100 mm (TL) in females and 119 mm (TL) in males (Prasadam, 1971;

Keshava et al., 1988). Size at first maturity in Pristolepis malabaricus Gunther, a non-

guarder have been determined to be 77 mm in males and 81 mm in females (Sherly,

1993).

2.4.2 Distibution of ova in the ovary

Gross picture of distribution of ova stocks in the anterior, middle and posterior

regions of ripe ovary remains almost same except for the slight variations in the

percentage composition of the node. Similar observations were made in Chanda

comersoni (Nair and Nair, 1983), Sphyraena jello (Krishna Das, 1992), Pristolepis

malabaricus (Sherly, 1993), Priacanthus hamrur (Sivakami et al., 2001).

2.4.3 Spawning frequency

Based on the distribution of ova stocks, P. marginata was found to release eggs

more than once during an extended period of spawning. Ova diameter frequency studies

revealed that this species comes under the category ‘C’ of Karekar and Bal’s

classification (1960), characterized by spawning more than once (multiple spawner)

during a protracted spawning season. It can be placed under the category II of Quasim

and Qayyum (1961). These fishes show protracted spawning season with individual

spawning more than once. Pristolepis malabaricus, which spawn in a slightly estuarine

habitat, also shows protracted spawning period, which coincides with the monsoon

season. It is classified under category B of Karekar and Bal (Sherly, 1993). On the

160

contrary, Etroplus suratensis spawn throughout the year with two peaks, February to

May and October to November (Prasadam, 1971; Keshava et al., 1988).

In P. marginata, ovary possessed a batch of ripe stock and intermediate ripening

stock in between the ripe and immature stocks. Ovary of P. marginata can be classified

as ‘asynchronous’, in which oocytes in all stages of development are present at the same

time. The oocyte size frequency distribution is continuous except in ripe ovaries, where

there may be a clear separation between the ripe and yolked oocytes. Similar pattern of

oocytes size frequency distribution was observed by Wallace and Selam (1981) in

sticklebacks.

The present results were further strengthened by captivity studies in which fishes

were reared for over two years and they were found to show protracted spawning

activity, in which fishes, during a single spawning activity extrudes eggs in three or four

batches.

2.4.4 Fecundity

Estimation of fecundity of fish is a prerequisite in successful breeding programme as

fecundity of a species is an indicator of reproductive potential of the species. Bagenal

and Braum (1978) had reported that fecundity in fish species characteristically varied

among individuals of the same size and age. Fagade et al. (1984) had also suggested that

fecundity variation may be due to differential abundance of food.

In the present study, absolute fecundity of P. marginata ranged from 1102 to

4965 in fishes whose size ranged from 66 to 104 mm SL. In repeat spawners, absolute

fecundity ranged from 1957 to 4344 (80 to 104 mm SL). These values are comparable to

161

the fecundity of Etroplus suratensis. Fecundity of Etroplus ranged from 600 to 6000

(Bhaskaran, 1946; Prasadam, 1971; Keshava et al., 1988). On the contrary, the fecundity

in a non-guarder, P. malabaricus ranged from 7814 to 19,000 in fishes whose size

ranges from 9.7 cm to 12 cm SL (Sherly, 1993).

Studies on fecundity shown that repeat spawners have larger fecundity than

recruit spawners. The number of eggs released increases with age and size ranging from

1102 in first time spawner to 4344 for the oldest fish observed. Fecundity shows strong

positive correlation with standard length and weight of the fish. It shows strong

correlation with weight of the ovary while least correlation is shown between fecundity

and ovary weight. Similar relationships were observed in P. malabaricus (Sherly, 1993)

and E. suratensis (Prasadam, 1971; Keshava et al., 1988).

Lower fecundity found in P. marginata may be explained on the basis of ‘K-

section’ (Mac Arthur and Wilson, 1967). K-section is correlated with low fecundity and

slow development. K-strategies tend to be multiple spawners who allocate a greater

proportion of reserve to the non-reproductive effort such as territoriality, nest building,

brooding and care of young, so tend towards greater efficiency.

2.4.5 Gonadosomatic index (GSI)

Gonadosomatic index (GSI) is a reliable indicator on gonadal maturity; as

naturally the weight of the gonad increases with maturity and when it spawns, there is a

reduction in the weight of the gonad on account of the release of gametes (deVlaming et

al., 1982). GSI is the indicative of fish spawning in temperate and tropical regions

162

(Bouain and Sian, 1983; Biswas et al.,1984). In natural habitats maximum GSI is the

sign of the breeding season of the fish (Rao, 1993; Hamza, 1980; Sharma, 1987). While

in captive conditions it could be reckoned as the time of spawning regardless of the

breeding season. Because, the physiological response of a species can be altered by

providing changes in environmental parameters in captive conditions (Munro et al.,

1990). Yoneda et al., (2001) stated that females of some species has allocation as high

as 25 % of the body weight to gonads. In the case of P.marginata, this was found to be

13 %.

Female Reproductive system

The present study reveals that the reproductive organs of P. marginata are built

on the usual percoid plan with paired ovaries, short oviduct opening out by the

urinogenital opening, the peculiarity being that the right lobe is conspicuously larger

than the left lobe. Similar observations made by Bennington (1936) on Betta

splendens,James (1946) on Lepomis macrochirus, Aravindan and Padmanabhan (1972)

on Tilapia mossambica, Sherly (1993) on Pristolepis malabaricus, Sivakami et al.,

(2001) on Priacanthus hamrur, Goswami and Dasgupta (2004) on Nandus nandus.

Male reproductive system

Asymmetry is shown in size and form of the two lobes of the testis of P.

marginata. Male reproductive organs are pinkish white during the younger stages and

creamish white on reaching the ripe stage. Partially spent testis appears dirty white with

163

blood shot. Same observations were made in Lepomis macrochirus (James, 1946), in P.

malabaricus (Sherly, 1993), in Nandus nandus (Goswami and Dasgupta, 2004).

2.4.6 Reproductive strategy

A complete knowledge of the reproductive system and the reproductive biology

of fishes are essential to understand the reproductive strategy of any given species. As

far the natural habitat of P. marginata is concerned, the different reproductive strategy

adapted by the species is well suited to thrive on the particular environment. The wide

spectrum of reproductive strategies supports a diversity of adaptive processes by which

species have adapted and populated the environment. In addition to aiding in assessing

fecundity, understanding these mechanisms of reproduction could also lead to greater

comprehension of the underlying mechanisms of variable fish recruitment (Murua and

Saborido-Rey, 2003). Reproductive potential is a measure of the capacity of a

population to produce viable eggs and larvae, and can be considered as the main

outcome of a reproductive strategy (Murua and Saborido-Rey, 2003).

P. marginata was found to possess an asynchronous type of ovary, because

oocytes of all stages of development are present without dominant populations. The

ovary appeared to be a random mixture of oocytes, at every conceivable stage. Such

ovaries may be found in iteroparous species, with protracted seasons and where yolk

accumulation, and hence oocyte development, relies mostly on the food available in the

environment at that moment (Hunter and Leong, 1981). Because the fish recruited and

ovulated the yolked oocytes in several batches over a protracted period during each

spawning season, it can be classified as a batch spawner. Batch spawning can be seen as

164

a strategy to release eggs over a long period of time increasing the survival probability

of offspring (Lambert and Ware, 1984).

Balon (1975) has proposed thirty two guilds to encompass all 28,000 living

species of fishes. The complexity of reproductive modes and strategies in fishes is

reflected in the construction of an ecological and ethological classification of

reproductive systems. As per his classification Pristolepis marginata belongs to the

Ecological classification of Guarders, ethological group of Nest builders and

morphotype of lithophils

28