Three experimental diets containing 14.9% (low carbohydrate; LC), 31.4% (medium carbohydrate; MC) and 42.3% (high carbohydrate; HC) of extruded wheat meal were fed to rainbow trout, Oncorhynchus mykiss, to investigate the significance of carbohydrate level on the rates of gastric evacuation and return of appetite (feed intake). Gastric evacuation measurements were performed by serial slaughter and recovery of digesta whilst X-radiography was used to estimate the rates of return of appetite. Gastric evacuation data of all three treatments were best explained by square root equations. The gastric evacuation rate of the LC group was significantly different (P0.05) between the emptying rates of the MC and HC groups. Three sigmoid models described the appetite revival data of the experimental groups. The interaction between these results displayed that a very close relationship exists between gastric evacuation and return of appetite in rainbow trout, irrespective of dietary carbohydrate level. It was claimed that rainbow trout as a sight feeder is likely to feed for stomach fullness in the short term regardless of the dietary composition.

Three experimental diets containing 14.9% (low carbohydrate; LC), 31.4% (medium carbohydrate; MC) and 42.3% (high carbohydrate; HC) of extruded wheat meal were fed to rainbow trout, Oncorhynchus mykiss, to investigate the significance of carbohydrate level on the rates of gastric evacuation and return of appetite (feed intake). Gastric evacuation measurements were performed by serial slaughter and recovery of digesta whilst X-radiography was used to estimate the rates of return of appetite. Gastric evacuation data of all three treatments were best explained by square root equations. The gastric evacuation rate of the LC group was significantly different (P0.05) between the emptying rates of the MC and HC groups. Three sigmoid models described the appetite revival data of the experimental groups. The interaction between these results displayed that a very close relationship exists between gastric evacuation and return of appetite in rainbow trout, irrespective of dietary carbohydrate level. It was claimed that rainbow trout as a sight feeder is likely to feed for stomach fullness in the short term regardless of the dietary composition.