Alternative plant protein sources in sea bass diets

A control diet (C) containing animal protein (mainly fish meal) was compared with 6 experimental diets containing different plant proteins (soybean meal, SM; rapeseed meal, RM; potato protein concentrate, PPC and a mix of the three vegetable protein sources, M). The plant protein replaced either 25 (1) or 50 (2)% of the animal protein with the exception of diet RM2 where the substitution rate was lowered to 35%, and in diet M where 55% of the total protein given was replaced in equal amounts by the three plant proteins. For the growth trial, which lasted 97 days, 528 European sea bass (initial live weight 107 ± 0,06g), distributed among 24 fibreglass tanks with three replicates per treatment, were used. The pelleted feed was distributed 5 times per day using an automatic dispenser. Energy, crude protein and crude fat digestibility values for fish meal and soybean meal were similar and not statistically different while the values for rapeseed meal and potato protein concentrate were significantly lower. Digestive utilization for NFE was higher in fish meal and decreased significantly in soybean meal, rapeseed meal and even more noticeably in potato protein concentrate. Diet digestibility values showed a similar trend with a clear worsening effect at the higher inclusion rates used. Diet M gave digestibility coefficients lower than those observed with diets C, SM1, SM2, RS1 and RS2 and higher than those of diets PPC1 and PPC2. Fish fed a diet in which 25% of the total protein was replaced by soybean had similar performances to those of the control group. On the other hand, sea bass fed diets SM2, RS1, RS2 and M had lower growth rates and worse feed utilization than those observed with the control. Finally, specific growth rates and food conversion efficiency in sea bass fed diets containing potato protein concentrate were poor because of the low palatability. These results show that soybean meal can substitute up to 25% of the total protein of the diet without any negative effect on sea bass performance.