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

Triplicate groups of juvenile American eel were fed to satiation herring me al-based diets containing 35, 39, 43, 47 and 51% crude protein (as fed basi s) for 84 days. Data were collected to determine the relationship between d ietary protein level and the following response variables: mean weight gain (MWG), specific growth rate (SGR), feed conversion ratio (FCR), nutrient d igestibility and nutrient retention. Highest MWG and SGR (P < 0.05) were ob tained when dietary protein was 47% and 51% with values (mean +/- SEM) of 1 4.2 +/- 0.66 g and 12.8 +/- 0.61 g for MWG, respectively, and values of 1.2 0 +/- 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% protei n and was significantly better than all other levels. Digestibilities of cr ude protein and energy were similar among the diets containing 39, 43, 47 a nd 51% protein with mean protein digestibility of 90.7 +/- 0.54% and mean e nergy digestibility of 90.3 +/- 0.60%. However, digestibility coefficients of the 35% protein diet were significantly lower (P < 0.05) at 84.9 +/- 0.9 7% 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% pro tein, while highest carcass lipid gain (P < 0.05) of 1.8 +/- 0.07 g/fish wa s achieved when feeding 47% protein. Little difference in carcass energy ga in was observed due to the different dietary protein levels. Based on all m easured criteria, the optimum level of dietary protein for juvenile America n eel is estimated to be 47% or 22 g digestible protein/MJ digestible energ y. (C) 2000 Elsevier Science B.V. All rights reserved.