Influence of dietary energy level on stomach emptying and appetite revival rates in rainbow trout, Oncorhynchus mykiss

D1, D2 and D3 diets containing 15.5, 12.5 and 9.0 MJ kg(-1) digestible energy concentrations were offered to rainbow trout (Oncorhynchus mykiss Walbaum, 1792), and the rates of gastric evacuation and feed intake were determined. Gastric evacuation determinations were achieved by slaughtering eight fish every 6 h until no residue was found in the cardiac stomach. Return of appetite experiments were conducted by re-feeding groups of trout every 6 h following the first feeding. The data provided from each process was modelled by regression analysis and compared statistically. Square root equations best explained the gastric evacuation data, whereas first-order models were used for the description of return of appetite. The gastric emptying slope of D1 was found to be different (P < 0.05) to the other two treatments, whilst no significance (P > 0.05) was apparent between the slopes of D2 and D3. Similarly, the return of appetite slope of D I was significantly different (P < 0.05) to the slopes of D2 and D3, although no noticeable difference (P > 0.05) was evident between the return of appetite slopes of D2 and D3. A close relationship between appetite revival and gastric evacuation rates in rainbow trout was established.