Turkish Journal of Biology




Rainbow trout (Oncorhynchus mykiss) were fed diets containing three different concentrations of crude protein (56.3%, 51.7% and 45.8%) and digestible energy (21.3, 20.3 and 18.8 MJ/kg), and the effects of dietary protein and energy level on gastric evacuation and return of appetite times were investigated. Gastric evacuation determinations were achieved by slaughtering 8 fish every 6 hours until no residue was found in the cardiac stomach of fish. Return of appetite experiments were conducted by re-feeding groups of trout every 4 or 6 hours following the first feeding. The data obtained from each process was modelled by regression analysis and compared statistically. For gastric evacuation modelling, square root models gave the best fits for the data set under examination. According to the square root fit for evacuation of all diets, no significant difference (P >0.05) was evident. One first-order and two sigmoid equations were used for the description of return of appetite data. Return of appetite slopes of all diets were also not observed to be significantly different (P >0.05). Regardless of the models employed, a very close relationship was apparent between appetite revival and gastric evacuation times in rainbow trout. The results indicated that gastric emptying time could be a major factor in the feed intake regulation whilst dietary protein and energy concentrations are likely to have a minor influence on the control of feeding.


Feed intake, high-protein diets, high-energy diets, gastric evacuation time, return of appetite, rainbow trout

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