Dietary substitution of soy and rapeseed protein concentrates for fish meal, and their effects on growth and nutrient utilization in gilthead seabream Sparus aurata L.

Soy and rapeseed protein concentrates (SPC and RPC) were evaluated as fish meal substitutes in gilthead seabream Sparus aurata L. diets. The protein c oncentrates were used to replace 30%, 60% and 100% fish meal, and effects o n feed intake, weight gain and feed gain ratio were determined in a 56-day growth trial. Some groups were then grown beyond 56 days, until all reached an average weight of 50 g. A comparison of body composition at 50 g showed no significant differences in protein and ash content among all fish, whil e lipid and energy contents were different. The 100% RPC and 60% and 100% S PC replacement diets had lower body lipid and energy contents compared with those of the control diet. Feed intake and weight gains were inversely rel ated to inclusion levels of plant proteins. Feed intake dropped to 52-72% o f that of the control treatment and weight gain to 46-61%. Energy retention followed this same trend, decreasing from ERV values of 53 to 44 with an i ncrease in dietary plant protein content. With the exception of 100% SPC su bstitution (PPV = 35), protein retention among treatments was similar (PPV = 37-39). These results suggest that both SPC and RPC may be promising prot ein sources for inclusion in seabream diets. The relative palatability of t hese plant proteins could be a limiting factor in their use.