Effect Of Starvation And Refeeding On Compensatory Growth Response Of Juvenile Black Sea Bream, Acanthopagrus Schlegelii

Effects of single phase of food deprivation and refeeding on metabolic parameters were studies in juvenile black seam bream, weighing 15.79±0.21 g. Fish were divided into four different starvation periods:5,10,15 and 20 days designated as D5,D10, D15, and D20.After starvation periods fish were fed to satiation twice a day until the end of the experiment. The duration of refeeding periods was 51 days for D5,46 days for D10, 41 days for D15 and 36 days for D20, which was dictated by the length of the fasting period. The control group (DO) was continually fed to satiation throughout the experiment. The experiment lasted 8 weeks. Fish in all the experimental groups were fed the same diet (40.89% crude protein and 14.27% crude fat). Each group was assigned to triplicate groups of 25 fish per tank in a completely randomized design. Fish were maintained in fiberglass tanks (600 L) and supplied with flowing seawater (3L min-1);temperature and salinity were 28±1℃and 29 g L-1, respectively. Dissolved oxygen concentrations were not below than 5.0 mg L'1 at any point. Fish were fed twice daily (0800 h and 1600h).Significant decrease in body weight was recorded as early as on day 10 of starvation. On day 20 this decrease was more pronounced, reaching lower value in comparison to the days,5-15 (P<0.05).The decrease in body length started on day 15 reaching the lowest value after 20 days of starvation (P<0.05).However, liver weight and hepatosomatic index (HSI) decreased very early on day 5,and remained stable from the day 5 to the day 20 (P>0.04). Survival was significantly affected by the length of starvation periods. Fish that starved for 20 days showed a lower survival rate than fish in control group, D5 and D10 (P<0.05),however survival rate from DO to D15 was not statistically different (P>0.05).A concomitant decrease in the whole body and muscle lipid content was also observed during this period, with a progressive decrease from day 10 to day 20 of starvation in whole body and from day 5 to day 20 of starvation in muscle. The extent of lipid decrease in the whole body content was less pronounced than the decrease in muscle content. In large contrast, moisture content in whole body and muscle increased progressively during starvation. After 20 days of starvation, moisture content in D20 was significantly higher than the value obtained in the control group (P<0.05). Enzymes activities (protease, lipase and amylase) decreased during starvation period, reaching the lowest value on day 20 (P<0.05).After 10 days of starvation, histological structure of stomach and foregut started exhibiting progressive changes.At day 20 marked degeneration of the submucosa tissue, villi, columnar epithelium, basement membrane, muscle fibres, circular muscle fibres and globlet cell were observed in the stomach and the foregut.Results obtained at the end of the refeeding periods showed that growth performance in continuously fed control group was significantly similar than those of the deprived groups D5,D10 and D15 (P>0.05).Feed intake did no differ from DO to D20 (P>0.05).Weight gain highly correlated with total feed intake. Feed conversion ratio (FCR) was the highest in the control group, D5,D10 and D15 (P>0.05), the lowest value was recorded in D20 in comparison to the control group (P>0.05).However, FCR from D5 to D20 was not statistically different (P>0.05).Protein efficiency retention (PER) of juvenile black sea bream from D5 to D15 were not significantly different from those of fish in D0 (P>0.05), but significantly higher than those of fish in D20 (P<0.05). The same result was obtained for the condition factor (CF).HSI, liver weight and body length did not differ among groups (P>0.05).After refeeding period chemical composition of whole body and muscle were restored, except for protein content in muscle. Protein content in muscle was only restored from D5 to D15 in comparison to the control group (P>0.05).Apparent digestibility of dry matter was significantly lower in D15 and D20 (P<0.05). Fish in D0, D5 and D10 exhibited a higher digestibility of dry matter. Apparent digestibility of protein from DO to D15 was significantly higher than that of fish in D20 (P<0.05).However, no significant difference was found for lipid digestibility among groups (P>0.05).Total protein and cholesterol (CHO) in the serum measured at the end of the refeeding period did not show any significant difference among groups (P>0.05).The value of glucose recorded from DO to D10 was significantly higher than that of fish in D15 and D20 (P<0.05).Triacylglycerol (TG), Glutamete oxaloacetate transaminase (GOT) and Glutamate pyruvate transaminase (GPT) among D0, D5 and D10 were also not statistically different (P>0.05).The lowest values were recorded in D15 and D20 in comparison to the control group (P<0.05).Growth hormone (GH) and ttiiodothyrinine (T3) measured in the serum among groups were significantly affected by food deprivation (P<0.05).Fish in the control group had a lower value of GH than the other groups (P<0.05), except with D5 (P>0.05).The highest value was reached only in D20 (P<0.05).The trend of GH and T3 was significantly opposite; the highest values were obtained in D0, D5 and D10 in comparison to D15 and D20 (P<0.05).However, value recorded in D15 was not statistically different to that recorded in D5 and D10 (P>0.05). The lowest value among groups was reached in D20 (P<0.05).The protease and lipase activities of liver of fish in D20 were significantly lower than that of fish in D0, D5 and D10 (P<0.05).In the foregut the highest values were observed for fish in DO and D5 (P<0.05), and from DO to D10 in the midgut (P<0.05). There was a slight decrease of amylase activity in the liver but not significantly different among groups (P>0.05). Low values were observed in the stomach, foregut and the midgut in D15 and D20, except in the midgut where the lowest value was only observed in D20 (P<0.05).Taking into consideration the results obtained in the present study, it can be concluded that juvenile black sea bream have the ability to fully compensate for 2 weeks (15 days) feed deprivation during the starvation period. The conclusion from current research would be useful to reduce feed costs in commercial aquaculture of juvenile black sea bream and to develop good feed management and husbandry strategies...