Metabolic consequences of chronic elevation of cortisol in the diet of yearling channel catfish, Irtalurus punciaius, were studied. Cortisol was incorporated into the diet in concentrations of 1, 10, 50 and lOOpg/g of food. This diet was offered at 3% of the body weight per day for 10 weeks. Fish were individually weighed and measured at 2-week intervals and feeding rates were adjusted. Body weight, liposomatic index and condition factor were significantly lower and food conversion was significantly higher in fish fed 50 or 100 pg cortisol/g of food when compared with controls. The hepatosomatic index of fish fed cortisol at the rate of lOOpg/g of food decreased significantly. Specific activity of hepatic tyrosine aminotransferase was significantly higher at the two highest cortisol doses. Long-term cortisol administration can reduce growth and condition factor by activating gluconeogenic mechanisms in which lipids and amino acids, rather than carbohydrates, are used for energy production. The metabolic effects of exogenous cortisol in this study offer an explanation for the decreased growth of fish under conditions that activate the secretion of endogenous cortisol.
Channel catfish (Ictalurus punctatus) were held on a 12-h light, 12-h dark photoperiod (light onset 0600 h) and fed a nonpurified diet daily at either 0730 or 1600 h or a half ration at both of these times of day. The feeding time conducive to total growth (0730 h) differed from that conducive to fattening (1600 h). Fish fed a half ration at both times of day had body weights similar to those fed a single early meal but also had high abdominal fat weights similar to those fed a single late meal. Feeding schedule appears to be an important factor in determining the metabolic fate of nutrients.
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