Performance of Rainbow Trout Fed Gelatin-Bound Diets of Fish Protein Concentrate of Casein Containing 25 to 45 Percent Herring Oil

Abstract

Five diets based on fish protein concentrate-gelatin (FPC), ranging in herring oil content from 25 to 45%, and one casein-gelatin based diet containing 35% herring oil were fed to rainbow trout (Salmo gairdneri) for 95 days to evaluate nutrient assimilation of diets with high caloric densities. Digestible energy densities of diets ranged from 4.36 to 6.19kcal/g. Diets were formulated to be isonitrogenous (38% crude protein). Alpha-cellulose, which is considered to be indigestible by fish, was the only carbohydrate used in formulation of diets. Weight gains were higher (P < 0.01) for fish fed the FPC than for fish fed the casein-gelatin diet. Oil level in the diet was highly related (P < 0.05) to feed conversion efficiency (FC; weight of feed consumed/live weight gain), having a correlation coefficient of -0.88. The FPC diet containing 35% herring oil had a higher FC (0.821, P < 0.05) than the casein diet with 35% herring oil (FC, 0.971). All FPC diets had a higher dietary energy conversion rates than the casein-gelatin diet (P < 0.01), which indicated that casein is limiting with respect to protein quality for trout. A trend for improving protein conversion was observed as the caloric density of the diet increased. The FPC diets were more efficient (P < 0.05) in supporting conversion of dietary protein into tissue than was the casein diet. The overall desirability of the fish as determined by an organoleptic taste panel was lower (P < 0.05) for fish fed diets with high levels of herring oil, but fell within acceptable limits.