Inclusion of plant-protein feedstuffs in aquaculture feeds has increased in recent decades, but the presence of indigestible carbohydrates and protease inhibitors in such feedstuffs can negatively affect their nutritional value to aquatic animals. Supplementation of exogenous enzymes in land animal feeds has been shown to influence feed intake, increase protein and energy digestibility, and improve growth rates and feed efficiency. However, information about the efficacy of enzyme additives in diets for farmed fish is still limited.
A 14-week digestibility trial was conducted to evaluate the effects of supplemental carbohydrase and protease enzymes in plant-based diets for Hybrid Striped Bass (HSB). Five test diets were formulated to contain 40% crude protein and 12% lipid with conventional soybean meal (SBM) or a combination of SBM and dried distillers grains with solubles as the main protein sources. To evaluate the effects of the enzymes additives, the following treatments were designed: no enzyme supplementation (negative controls), supplemental carbohydrase and protease (CP+), and supplemental carbohydrase and protease at 2X the recommended supplementation levels by the manufacturer (CP++). All experimental diets contained yttrium oxide (Y2O3) at 1% as the digestibility marker. Each diet was fed once daily to apparent satiation to quadruplicate groups of ~20 juvenile HSB (~100 g/fish) stocked in 180-L polyethylene tanks operating as a recirculating aquaculture system. Fecal samples were collected by stripping once a week until ~3 g dried fecal matter was obtained. Element and proximate composition analyses of the experimental diets and fecal matter are currently underway and apparent digestibility coefficients will be presented.