Inclusion of plant-protein feedstuffs in aquaculture feeds increased in recent decades, but the presence of indigestible carbohydrates and protease inhibitors in such feedstuffs can negatively affect their nutritional value to fish. While supplementation of exogenous enzymes in land-animal feeds can improve digestibility, growth rates, and feed efficiency, the efficacy of these additives in aquaculture feeds has been inconsistent. The objective of this study was to evaluate the effects of protease and carbohydrase additives in plant-based diets on the digestibility, production performance, and protein and energy utilization of hybrid striped bass (HSB).
Digestibility Trial: a 14-week digestibility evaluation was conducted using advanced juvenile HSB (~ 100g/fish) fed diets containing different levels of the enzymes. Fish in each of four tanks were fed one of five randomly assigned diets to apparent satiation once daily. Fecal matter was collected by stripping all fish once a week at ~5 h postprandial. While no significant differences in the ADCs of dry matter, protein, and GE were detected among treatments, supplementation of carbohydrase significantly increased the ADC of NDF.
Growth Trial: in the subsequent eight-week growth evaluation, quintuplicate groups of 20 HSB juveniles (9g/fish) were fed one of seven randomly assigned diets: six plant-based diets containing different levels of supplemental carbohydrase; and a fish meal-based diet (FM-30). No differences in survival (95-100%) were found among groups. Supplementation of carbohydrase to the plant-based diets did not affect growth, feeding rate, and feed efficiency of HSB. When compared to FM-30-fed groups, HSB fed the plant-based diets consumed relatively more feed but displayed similar production performance. Additional results on whole-body proximate composition, and protein and energy retention efficiencies will be presented.
Based on the current results, supplementation of carbohydrase additive to plant-based diets may slightly improve carbohydrate digestibility by HSB, but supplementation of protease to these formulations does not seem beneficial.