The use of hydrolyzed protein from nonnative carp species to improve growth and survival in Walleye larval aquaculture

Abstract Objectives Larval fish of many species lack fully developed digestive systems at the start of feeding and thus require diets that accommodate their limited digestive capacity. Larval culture of Walleye Sander vitreus is often characterized by low survival and variable growth performance, and diets tailored for their specific requirements are not available. This study assessed the use of protein hydrolysates derived from muscle tissue of nonnative carp species (Hypophthalmichthys spp.) generated using digestive enzymes from adult Walleye. Methods Two feeding trials tested the relative performance of hydrolyzed and intact carp-derived proteins as first-feed diets (from first exogenous feeding at 4 d posthatch to 34 d posthatch) and as weaning diets (transitioning from live brine shrimp Artemia spp. nauplii at 22–44 d posthatch). Survival, growth performance, feed acceptance, swim bladder inflation, and deformity rate were monitored and compared amongst treatments. Results In the first-feeding trial, Walleye fed the hydrolysate diet had significantly improved growth performance relative to those fed the intact protein diet, but survival did not differ significantly among treatments. In the weaning trial, growth performance and survival did not differ between hydrolyzed and intact diets, but both diets supported better growth than feeds with marine-derived hydrolyzed proteins. The best growth performance in both trials was achieved with a currently available commercial starter diet. Conclusions The improved growth performance of the hydrolyzed diet in the first-feeding trial highlights the importance of providing diets suitable for the limited gut capacity of Walleye larvae in early development (prior to 22 d posthatch). Given the lack of differences in growth performance during the weaning trials, digestive capacity requirements appear less important in later larval development. Although proteins derived from nonnative carp hydrolyzed using same-species digestive enzymes show promise in Walleye larval culture diets, further refinement is needed to match the performance of currently available commercial diets. This study also presents a novel approach utilizing muscle from nonnative species and byproducts from processing plants in the form of fish digestive tracts.