Dietary protein requirement of juvenile American eel ( Anguilla rostrata) fed practical diets

Abstract

Triplicate groups of juvenile American eel were fed to satiation herring meal-based diets containing 35, 39, 43, 47 and 51% crude protein (as fed basis) for 84 days. Data were collected to determine the relationship between dietary protein level and the following response variables: mean weight gain (MWG), specific growth rate (SGR), feed conversion ratio (FCR), nutrient digestibility and nutrient retention. Highest MWG and SGR ( P<0.05) were obtained when dietary protein was 47% and 51% with values (mean±SEM) of 14.2±0.66 g and 12.8±0.61 g for MWG, respectively, and values of 1.20±0.04%/day and 1.13±0.05%/day for SGR, respectively. Optimum FCR ( P<0.05) of 1.17±0.05 g feed/g gain was achieved by feeding 47% protein and was significantly better than all other levels. Digestibilities of crude protein and energy were similar among the diets containing 39, 43, 47 and 51% protein with mean protein digestibility of 90.7±0.54% and mean energy digestibility of 90.3±0.60%. However, digestibility coefficients of the 35% protein diet were significantly lower ( P<0.05) at 84.9±0.97% for protein and 85.2±0.98% for energy. Highest carcass protein gain ( P<0.05) of 2.2±0.11 g/fish was achieved when feeding 47% and 51% protein, while highest carcass lipid gain ( P<0.05) of 1.8±0.07 g/fish was achieved when feeding 47% protein. Little difference in carcass energy gain was observed due to the different dietary protein levels. Based on all measured criteria, the optimum level of dietary protein for juvenile American eel is estimated to be 47% or 22 g digestible protein/MJ digestible energy.