Effect of sublethal concentrations of copper on the growth performance

of Oreochromis niloticus

By A. Ali1, S. M. Al-Ogaily2, N. A. Al-Asgah1 and J. Gropp3

1Zoology Department, College of Science, King Saud University, Riyadh, Saudi Arabia; 2Natural Resources and EnvironmentalResearch Institute, King Abdulaziz City for Science and Technology, Riyadh, Saudi Arabia; 3Institute of Animal Nutrition,Nutritional Diseases and Dietetics, Faculty of Veterinary Medicine, University of Leipzig, Leipzig, Germany

Summary

The study evaluated the effect of different sublethal concen-trations of copper in water (0, 0.15, 0.3 and 0.5 p.p.m.) on thebehavioural response, growth performance, and whole body

and liver composition of Oreochromis niloticus. Hyperactivityand reduced exploratory behaviour were observed when fisheswere subjected to different levels of copper in water as

compared with the control. Fish refused to accept the feedimmediately after exposure and only began taking it up afterabout 4–5 h as compared with the control. Weight gain,

specific growth rate and condition factor (k) decreasedsignificantly (P < 0.05) as compared with the control; thisdecrease was linearly correlated with the increase of copper

concentration in water. Exposure of the fish to different copperconcentrations in water significantly (P < 0.05) reduced theirfeed consumption as compared with the control. Values for thefeed conversion ratio increased (P < 0.05) whereas the protein

efficiency ratio and net protein retention values decreased(P < 0.05) with the copper level increase in water. Thehepatosomatic index increased with the copper concentration

increase in water. Body moisture and ash contents were thehighest (P < 0.05) whereas the fat and gross energy contentswere the lowest (P < 0.05) in fish reared in water containing

0.5 p.p.m. of copper as compared with others. No significant(P < 0.05) differences were observed in the whole body crudeprotein content of fish exposed to different concentrations ofcopper as compared with the control. Liver moisture and ash

contents increased (P < 0.05) whereas the crude protein, fat,nitrogen free extract and gross energy contents decreased(P < 0.05) when the fish were exposed to different concentra-

tions of copper as compared with the control. The liverglycogen level decreased whereas the copper level in the wholebody and liver increased significantly (P < 0.05) with the

copper concentration increase in water.

Introduction

Copper is one of the most common environmental andbiotoxic pollutants. Anthropogenic input is the major sourceof copper concentration (Nriagu, 1988). It causes a compar-

atively large disturbance in the osmoregulation of freshwaterfish, even under chronic exposures. The decreased plasmaosmolality in freshwater fish exposed to copper is associated

with a rise in blood volume and tissue water content. Copperexposure to fish can result in degeneration of mechanorecep-tors and chemoreceptors (Gardner and LaRoche, 1973).

Copper acts as a catalyst in many enzyme systems, mainly

for cytochrome oxidase and electron carrier plastocyanin.Copper is strongly taken up by various fish liver mitochondriaby an energy-dependent system. The large number of copper-

containing enzymes and glycoproteins in fish probably accountfor the diversity of biological effects. Bioaccumulation andtoxicity of copper depends on its chemical form and dissolved

concentration. Free cupric ion (Cu++) is the most toxic formof copper in natural waters (Flemming and Trevors, 1989). Asionic copper inhibits a number of enzymes, the basis of copper

toxicity may represent diminished enzyme activity.1 Somiri (1982) concluded that acute toxicity of copper inOreochromis niloticus was more dangerous than mercury andzinc. Daramola and Oladimeji (1989) reported that the residual

accumulation of copper in the tissues of Clarias anguillaris andO. niloticus was directly related to the concentration andduration of the exposure. Gupta and Rajbanshi (1991)

reported that even at very low concentrations, copper wasmore toxic to fish than cadmium. Rajkumar and Das (1991)observed that glycogen level dropped significantly in the

muscles following heavy metal exposure. The body length andweight of different Tilapia species (O. galilaeus, O. niloticus andTilapia zillii) decreased when subjected to chronic sublethal

doses of copper sulphate (Draz et al., 1993). Pelgrom et al.(1994) observed that the nutritional status of fish influencedthe accumulation of metals; they reported that the exposure toeither copper or cadmium not only increased the whole body

content of these metals but also influenced the concentrationof other metals present in the fish. Tilapia was found to bemore copper-tolerant than rainbow trout (Pelgrom et al., 1990,

1995).The copper content of tapwater is normally well within the

acceptable levels but may exceed this because of exposure to

copper tubing and tanks. The copper concentration in groundwater samples from the cities of Riyadh and Dhahran, SaudiArabia has been reported to be on the average 0.036 and

0.055 mg L)1, respectively (Sadiq and Hussain, 1997). Corro-sion of the distributional network, however, may deterioratethe drinking water quality (Alam and Sadiq, 1989; Sadiq et al.,1997). Sadiq and Hussain (1997) reported that the concentra-

tion of copper in drinking water increased as a function ofutility copper pipe length. The wide use of high concentrationsof copper salts as algaecides and fungicides in fisheries and

agriculture may also create pollution problems.Tilapia respond well to aquarium culture and can tolerate a

wide range of environmental conditions (Chervinski, 1982;

Al-Asgah and Ali, 1997). Based on production per unit areaand food conversion efficiency, they are being labelled as

J. Appl. Ichthyol. 19 (2003), 183–188� 2003 Blackwell Verlag, BerlinISSN 0175–8659

Received: November 1, 2001Accepted: May 15, 2002

U.S. Copyright Clearance Centre Code Statement: 0175–8659/2003/1904–0183$15.00/0 www.blackwell.de/synergy

�aquatic chicken�. Tilapia have recently been introduced inSaudi Arabia – production potentials are still to be explored

under local conditions. There is fairly extensive data on thetoxicity of copper in salmonids but no comparable data fornon-salmonid species is available. Keeping in view the

importance of copper as a common environmental andbiotoxic pollutant, and the significance of Tilapia as afreshwater fish, the present study was conducted to evaluatethe effects of sublethal concentrations of copper on the growth

performance of O. niloticus.

Materials and methods

Oreochromis niloticus with an average weight of 36.00 ±1.92 g were collected from the fish hatchery of the King

Abdulaziz City for Science and Technology (KACST) Deerab,Riyadh. The fish were acclimatized to the experimentalconditions for a period of 2 weeks before the start of theactual experiment. During this period they were kept on the

same standard diet as fed previously at the hatchery. Todetermine their initial body composition, 30 randomly selectedfish (divided into three replicates of 10 fish in each) were killed

immediately. After recording their body weight and length,they were stored at )30�C for proximate analysis at a laterstage. A total of 120 fish was then randomly divided into four

different groups (A, B, C and D) with three replicatescontaining 10 fish in each replicate. Each group of fish wasthen transferred to glass aquaria (100 · 42 · 50 cm) contain-

ing 110 L of well-aerated tapwater and having four differentconcentrations of copper in the water. Groups A, B, C and Dwere assigned to different copper concentrations in the wateri.e. 0, 0.15, 0.3 and 0.5 p.p.m., respectively. Group A contain-

ing normal tapwater (without any additional copper) acted asa control. To maintain the required level of copper concen-tration in the water tanks, a stock solution of copper sulphate

containing 1000 p.p.m. of copper (i.e. 3.9295 g of CuSO4Æ5-H2O per litre) was prepared. The normal tapwater on analysisshowed 0.029 ± 0.011 mg L)1 of copper. Water temperature

in the different aquaria was maintained at 28 ± 0.5�C througha thermostatically controlled heating system. All aquaria werefitted with a waste filtration facility. Compressed air was usedto maintain the oxygen supply. Water quality parameters were

monitored regularly throughout the experiment. Valuesranged for pH (7.1–8.0), dissolved oxygen (5.6–6.7 mg L)1),ammonia nitrogen (0.12–0.20 mg L)1), nitrite nitrogen (0.33–

0.58 mg L)1) and for alkalinity as CaCO3 (235–250 mg L)1).

Fish were fed a standard diet containing 12.0% casein,25.0% fishmeal, 15.0% soyabean meal, 25.0% maize grain,

2.0% codliver oil, 5.0% corn oil, 11.0% dextrin, 2.0% gelatine,2.0% mineral mixture and 1.0% vitamin mixture. The diet wasprepared similar to that as described by Al-Asgah and Ali

(1994). The proximate chemical composition of the dietindicated 92.2% dry matter, 39.2% crude protein, 2.2% crudefibre, 11.7% total fat, 11.1% ash, 35.8% nitrogen-free extract(NFE) and 19.9 MJ kg)1 gross energy on a dry matter basis.

The diet was offered ad libitum twice daily to satiety. Toexactly quantify the amount of feed intake, uneaten portionsof the diet were immediately siphoned out, dried and weighed.

Daily feed intake and fortnightly weight gains were recorded.The 7-week experiment was conducted under artificial lightwith a light and dark cycle of 12 : 12 h. Soon after the transfer

of fish to the experimental tanks, their behavioural responsewas observed. At the end of the experimental period all fishwere killed and their body weights and lengths recorded. Five

fishes from each tank were dissected and their livers removedand weighed and preserved at )30�C for further analysis. The

liver glycogen was determined immediately according to themethod of Kemp and Kits van Heijiningen (1945). Todetermine the whole body composition, the remainder of the

fish was cut into pieces and minced through a meat grinder,and the homogenized samples were immediately frozen at)30�C for further analysis. The proximate chemical composi-tion was determined according to the methods of the Associ-

ation of Official Analytical Chemists (1990). To determine thecopper concentration in the fish and liver, samples wereprepared by wet digestion procedure and analysed with the aid

of the Atomic Absorption Spectrophotometer (2 Perkin ElmerModel 3280) as described in the manual (Perkin Elmer, 1996).The gross energy content of fish was calculated from the fat

and protein contents using the equivalents of 39.54 MJ kg)1

for crude fat and 23.64 MJ kg)1 for crude protein (Kleiber,1975). The factor used for the NFE was 17.15 MJ kg)1. Feedconversion ratio (FCR), specific growth rate (SGR), protein

efficiency ratio (PER), net protein retention (NPR) andhepatosomatic index (HSI) were calculated as follows:

Feed conversion ratio¼ gram feed dry matter consumed pergram weight gain

Specific growth rate (as percentage of body weightgain per day)¼ 100 · [ln final weight (g)

) ln initial weight (g)]

/time (days)Protein efficiency ratio¼ liveweight gain (g)

/protein consumed (g)Net protein retention¼ (increase in carcass protein

/protein fed) · 100Hepatosomatic index¼ (liver weight/fish weight) · 100

The condition factor (k) was calculated according to theequation k¼ [W (g)/L (cm)3] · 100, where W is the wet weight

of fish in grams and L is the length in centimeters. The dataso collected was subjected to statistical analysis using theanalysis of variance technique and the mean values compared

by Fisher’s Least Significant Difference (3 LSD) test accordingto Snedecor and Cochran (1989).

Results

The study on the behavioural response indicated that the fisheswere uneasy and showed restlessness when exposed to different

copper concentrations as compared with the control. Hyper-activity and reduced exploratory behaviour was observed.After about 1 h some of the fishes showed lethargic behaviour

and about 25% showed the tendency of settling downmotionless at the bottom of the aquarium. Alternatively,about 20% of the fish came to the upper surface of the water

and started taking the atmospheric oxygen with wide-openmouths. This state remained for about 4 h; thereafter in allexperimental groups, the fish again started showing the activebehaviour. However, with the passage of time about 20% of

the fish in groups C and D (exposed to 0.3 and 0.5 p.p.m. ofCu) again showed the behaviour of settling down motionless atthe bottom. The fish in group B (exposed to 0.15 p.p.m. of Cu)

showed almost the same comparable behaviour as the fish inthe control group. After about 24 h, the fish appeared to haveacclimatized to the new environment as about 85% were

behaving normally as in the control. One fish from each group(B, C and D) died after 24-h exposure. One additional fishfrom group D died after 48 h. No further mortality occurred

184 A. Ali et al.

during the experiment. The feed offered was not taken up bythe fish when immediately exposed to different copperconcentrations as compared with the control; however, theystarted taking some food after about 4–5 h.

Results on the growth performance of O. niloticus subjectedto different sublethal concentrations of copper are presented inTable 1. Significant (P < 0.05) differences were observed in the

total weight gain and SGR of fish reared in water containingdifferent concentrations of copper as compared with thecontrol. Weight gain and SGR decreased linearly with the

increase of copper level in the water. The body conditionfactor of fish reared in water containing different concentrationof copper also decreased significantly (P < 0.05) as compared

with the control. However, no significant differences wereobserved in the body condition factor of fish reared in watercontaining 0.15 and 0.3 p.p.m. of copper (i.e. between groupsB and C). Exposure of the fish to different copper concentra-

tions in water significantly (P < 0.05) reduced feed consump-tion as compared with the control – a direct correlation withthe levels of copper concentration in the water. The FCR

values increased with the level of copper concentration inwater, indicating poor utilization of food in the fish. The PERand NPR values decreased (P < 0.05) with the increase of

copper levels in the water. The HSI values also differedsignificantly (P < 0.05) among different groups. However, nosignificant (P < 0.05) differences were observed between theHSI values for fish reared in water containing 0.15 p.p.m. of

copper and the control group. Similarly, the HSI values forfish reared in water containing 0.3 and 0.5 p.p.m. of copper didnot differ (P > 0.05).

Data on the body composition of fish subjected to varioussublethal concentrations of copper are given in Table 2. Thebody moisture content of fish reared in water containing

0.5 p.p.m. of copper (group D) was the highest and differedsignificantly (P < 0.05) from groups A, B and C. No significant(P < 0.05) differences were, however, observed in the bodymoisture content of fish among the groups (A, B and C) reared

in water containing 0, 0.15 and 0.3 p.p.m. of copper. The bodycrude protein content of fish exposed to different copperconcentrations in water did not differ (P > 0.05) as compared

with the control group. The fish reared in water containing0.5 p.p.m. of copper (group D) showed the lowest body fatcontent, whereas no significant (P < 0.05) differences were

observed in groups A, B and C. On the contrary, the relativebody ash content of fish reared in water containing 0.5 p.p.m.of copper (group D) was the highest. No significant differences

were, however, observed in the body ash content of fish ingroups A, B and C. The results on the gross energy content offish were similar to those of fat content. The fish body copperlevel increased significantly (P < 0.05) with the increase of

copper concentration in water. The increase in the whole bodycopper level was directly proportional to the copper ionconcentration in the water.

Data on the chemical composition of liver are presented inTable 3. The liver moisture content of fish exposed to differentcopper concentrations in water increased as compared with the

control. However, no significant differences were observedbetween the liver moisture content of fish exposed to0.15 p.p.m. of copper in water (group B) and the control(group A). Similarly, the liver moisture content of fish in

groups C and D (exposed to 0.3 and 0.5 p.p.m. of copper) didnot differ (P < 0.05) significantly. The liver crude protein andfat contents of fish exposed to different copper concentrations

in water decreased as compared with the control. However, nosignificant (P < 0.05) differences were observed in the crudeprotein and fat contents of liver between groups A and B

Table 1Effect of sublethal concentrations ofcopper on the growth performance ofOreochromis niloticus

Parameters/groups A B C D SE

Initial weight (g fish)1) 36.74 36.10 35.88 35.77 ±1.61NS

Final weight (g fish)1) 70.39a 61.42b 51.57c 48.63d ±1.89Total weight gain (g fish)1) 33.65a 25.32b 15.69c 12.86d ±1.27Specific growth rate (%) 1.33a 1.08b 0.74c 0.61d ±0.06Condition factor (k) 2.71a 2.56b 2.48b 2.27c ±0.18Total feed consumed (g fish)1) 51.81a 46.20b 38.09c 34.83d ±1.75Feed conversion ratio 1.54d 1.82c 2.43c 2.71a ±0.23Protein efficiency ratio 1.78a 1.51b 1.13c 1.01d ±0.12Net protein retention (%) 26.67a 23.84b 17.46c 15.85d ±1.33Hepatosomatic index (%) 1.23b 1.31b 1.45a 1.51a ±0.13

SE, pooled standard error; NS, non-significant; a–d, different superscripts in the same row meanssignificant at 5%.

Table 2Data on the body composition of Oreochromis niloticus exposed todifferent sublethal concentrations of copper (on per cent wet basis)a

Parameters/groups A B C D SE

Moisture 73.35b 73.56b 73.44b 74.53a ±1.29Crude protein 15.18 14.94 14.95 14.82 ±0.53NS

Total fat 5.30a 5.76a 5.43a 4.83b ±0.44Ash 5.23b 4.98b 5.15b 5.61a ±0.38Gross energy (MJ kg)1) 5.68a 5.81a 5.68a 5.41b ±0.34Copper (lg g)1) 2.89d 3.73c 5.47b 8.98a ±0.87

aComposition of the fish killed in the beginning of the experiment(moisture 74.65%; crude protein 14.71; fat 5.09; ash 4.81 and grossenergy 5.49 MJ kg)1). SE, pooled standard error; NS, non-significant;a–d, different superscripts in the same row means significant at 5%.

Table 3Data on the proximate chemical composition of fish liver (on per centwet basis)

Parameters/groups A B C D SE

Moisture 76.50b 76.80a 78.45a 78.23a ±0.81Crude protein 15.77a 15.36a 14.43b 14.31b ±0.61Total fat 2.31a 2.21ab 2.16b 2.09b ±0.23Ash 1.69b 1.67b 1.61b 1.95a ±0.17Nitrogen free extract 3.73a 3.96a 3.35b 3.42b ±0.23Gross energy (MJ kg)1) 5.28a 5.18a 4.83b 4.80b ±0.26Glycogen (mg g)1) 6.08a 5.43b 5.31b 5.07c ±0.26Copper (lg g)1) 10.92d 16.27c 24.41b 38.34a ±1.39

SE, pooled standard error; NS, non-significant; a–d, different super-scripts in the same row means significant at 5%.

Effect of copper concentrations on Oreochromis niloticus 185

(exposed to 0.15 p.p.m. of copper as compared with thecontrol). Similarly, the groups exposed to 0.3 and 0.5 p.p.m.

of copper did not show any significant (P < 0.05) difference intheir liver crude protein content. Overall, the copper level inwater did not affect (P < 0.05) the liver fat content. Fish

exposed to 0.5 p.p.m. of copper showed the highest ash contentin the liver. The ash content of liver in other groups however,did not differ (P > 0.05) as compared with the control. Nosignificant differences were observed in the NFE content of fish

liver reared in water containing 0.15 p.p.m. of copper ascompared with the control. The NFE content of liver decreasedsignificantly in fish subjected to 0.3 and 0.5 p.p.m. of copper

concentration (groups C and D) as compared with the control.No significant differences were, however, observed in the NFEcontent of liver in both groups C and D. Fish exposure to

sublethal concentrations of copper in the water significantlyaffected the liver copper level that increased linearly with theincrease of copper concentration in the water. On the contrary,the glycogen level in the liver decreased significantly with the

copper concentration in water as compared with the control.The differences in the liver glycogen level between groups B andC were, however, not significant (P < 0.05).

Discussion

Many metals apparently stimulate the activities in fishes byprobably acting as a physical irritant to a potentially wideassortment of external tissues, causing an elevated metabolic

rate (Scarfe et al., 1982). Fish respond immediately to thepresence of copper and show hyperactivity and reducedexploratory behaviour (Steele, 1983; Koltes, 1985). Drum-mond et al. (1973) reported that copper at low sublethal

concentrations stimulated the locomotor activity in brooktrout, Salvelinus fontinalis. The behavioural changes observedduring this study are in close conformity with these findings.

Al-Akel (1987) and Al-Kahem (1989) also reported similartypes of behavioural changes in O. niloticus when subjected todifferent copper concentrations. The rising of the fish to the

upper surface of the water with wide-open mouths indicatethat they might be short of oxygen when exposed to differentcopper concentrations. The level of tolerance in fish dependson a number of factors such as alkalinity, pH, total hardness,

temperature and copper concentration in water and is species-specific. Temperature produces complex effects, but elevatedthermal levels increase fish sensitivity to copper. Lett et al.

(1976) noted a virtual cessation of eating upon initial exposureto copper. They reported that over a period of 10–40 daysthere appeared to be an acclimation to the copper and that the

fish appetite and growth returned to normal. The speed ofreturn to normalcy is inversely proportional to the copperconcentration in the water. Colgan (1973) presented evidence

that high levels of glucose in blood suppressed fish appetite.The higher the level of blood glucose, the lesser the foodintake. These hormonal changes cause mobilization of liverglycogen into blood glucose, so in essence, the system may be

fooled into accepting the caloric intake as being more thanadequate. As copper causes �metabolic masking�, the increasedcost of maintenance would leave fewer calories for growth

(Waiwood and Beamish, 1978).The changes in the maintenance cost of fish are still not well

explained. Exposure to copper causes a reduction in food

consumption, at least temporarily. It also increases themetabolism in some of the non-muscular tissues (e.g. liverand gills) while depressing the spontaneous muscular activity.

This latter effect may be a response to lowered food intake andcould also involve some effects of metal on the central nervous

system. With close coupling between the metabolic rate andgrowth, changes in the latter are to be expected when themetabolism is altered. Glycogen breakdown is accelerated and

copper inhibits glycolysis. Sastry and Gupta (1978) reportedhyperglycaemia in Channa punctatus exposed to HgCl2 becauseof enhanced liver glycogenolysis. The reduction in glycogenreserves in the tested tissues of exposed animals suggest that

glycogenolysis releases glucose into the circulatory system tomeet the increased energy demand during stress conditions.The mode of action of copper on fish is not clear, but lethal

concentrations may damage the gill, affect cell processes andenzyme activity, and cause liver and kidney disorders. Copperaccelerates the oxidation of reduced glutathione possibly by

stimulating the hexose-mono-phosphate shunt pathway. Whenfresh water teleosts are exposed to excess copper, mucuscoagulates in the gill cavity, glycogen falls in the liver, brainand the muscles but rises in the kidney. There is some evidence

that the depression in the response of chemoreceptors, increasein cough frequency, respiration and activity, and reduction infeeding observed at sublethal concentrations are only transit-

ory (Gardner and LaRoche, 1973, Lett et al., 1976).The decrease in weight gain and SGR with copper concen-

tration increase in water observed during this study agree with

these reported results for other species. The feed consumptionand the efficiency of feed conversion was reduced significantlyand did not return to normal until the end of the experiment,

even when the fish appeared to have acclimatized to the copperexposure. The PER and NPR values also decreased, indicatingpoor utilization and assimilation of proteins. The increase inHSI values showed an increase in the liver metabolism.

Muthukrishnan et al. (1986) reported that the rate of feeding,absorption and conversion of nutrients in Cyprinus carpiodecreased significantly when fed ad libitum and reared in media

containing sublethal concentrations of HgCl2. The rate ofdecrease was linearly correlated with the concentration ofHgCl2 in the medium. Muthukrishnan et al. (1986) observed

that at the highest tested sublethal concentration (0.304 p.p.m),the gross production efficiency of fish was about eight timesless than fish reared in tapwater.The decrease in the glycogen content of liver of fish exposed

to different concentrations of copper in this study confirm thehypothesis of Muthukrishnan et al. (1986) and agree with thereported results for other fish species. Liver is the primary

organ for the biotransformation of organic xenobiotics andprobably also for the detoxification and excretion of harmfultrace metals. The mobilization of liver glycogen into the blood

stream is controlled by glycolytic enzymes and plays asignificant role in glucose turnover. James et al. (1992) foundsuppression of succinate dehydrogenase (4,5 SDH) and elevation

of glycerol-3-phosphate dehydrogenase (4,5 GDH) activities inO. mossambicus (Peters) exposed to sublethal levels of Cu, Znand Cd. This indicated a high energy demand in the liver tobring about a metabolic coordination for the continuation of

the detoxification mechanisms. James and Sampath (1995)found that liver showed maximum reduction of tissue glycogenfollowed by gill and muscle in Heteropneustes fossilis exposed

to sublethal concentrations of copper and ammonia individu-ally or in combination. The results of the present study agreewith these findings.

Data on the body composition of fish and factors affectingthem allow the assessment of fish health and determine theefficiency of transfer of nutrients from the feed to the fish

186 A. Ali et al.

(Haard, 1992). The exposure of fish to different sublethalconcentrations of copper ions in water affected their whole

body and liver composition. The accumulation of copper in thebody and liver of fish increased linearly, whereas the glycogenlevel in the liver decreased with the copper ion concentration in

water. Daramola and Oladimeji (1989) reported that theresidual copper accumulation in tissues of C. anguillaris andO. niloticus was directly related to the exposure concentrationand duration of the exposure. Felts and Heath (1984) and

Buckley et al. (1982) also reported that the liver copperconcentration in fish steadily increased with the exposure time.There are, however, species-specific differences in copper

accumulation levels. The excess of copper is, in principle,accumulated in the liver. Similar results have also beenreported for C. punctatus (Sastry and Gupta, 1978), Platicht-

hys flesus L. (Stagg and Shuttleworth, 1982) and catfish,H. fossilis (James and Sampath, 1995). The reduction inglycogen reserves suggests glycogenolysis that releases glucoseinto the circulatory system to meet the increased energy

demand during stress conditions. James and Sampath (1995)reported a decrease in protein content and increase in theamino acids content of muscles, gills and liver of H. fossilis.

Proteolysis in the liver may occur during toxic stress (Kabeer,1979; Sreedevi et al., 1992; James and Sampath, 1995). Resultsof the present study indicated a decrease only in the protein

content of the liver, whereas the whole body protein contentwas not affected at these sublethal concentrations.

Dedication

This paper is dedicated to Prof. Dr Richard Mueller incelebration of his 90th birthday. Prof. Mueller is a Professor

Emeritus, Institute of Animal Nutrition, University of Bonn,Germany.

Acknowledgement

We wish to express our thanks to King Abdulaziz City for

Science and Technology (KACST) for the supply of fish andfor the provision of other necessary facilities.

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Author’s address: Amanat Ali, Zoology Department, College ofScience, King Saud University, PO Box 2455,Riyadh 11451, Saudi Arabia.Current address: Dr Amanat Ali PAg, CAC,Director Technical Services, BioNutriAg Consult-ant, 567 Scarb. Golf Club Road, # 1611, Toronto,Ontario M1G 1H5 CanadaE-mail: amanata@hotmail.com

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