Fishery wastes as feed additive for the red claw crayfish Cherax quadricarinatus: Impact on growth, biochemical composition, and digestive activity

Abstract

One of the challenges in aquaculture is reducing the use of fishmeal to alleviate pressure onaquatic ecosystems while maintaining protein quality and digestibility. A promising approach isthe supplementation of diets with exogenous enzymes, a strategy widely used in aquaculturenutrition but scarcely explored in crustaceans. This study aimed to evaluate the effects of a dietcomposed of 65 % plant-based and 25 % animal-based ingredients, supplemented with a multienzyme extract derived from discards of the native Argentine shrimp Pleoticus muelleri, on juveniles of the red claw crayfish, Cherax quadricarinatus. Growth performance, endogenous digestiveenzyme activities, and biochemical reserves (proteins, lipids, and glycogen) in hepatopancreasand pleon muscle were analyzed. Sixty-two crayfish weighting ⁓1.5 g were assigned to one of thefollowing treatments: a control diet (C) or a diet supplemented with multienzyme extract (E).Crayfish were individually housed under optimal growing conditions and fed daily 3 % of theirbody mass; deaths and molts were recorded throughout the experiment. At day 45, fifteen replicates from each treatment were selected, weighed, anesthetized, and sacrificed. The hepatopancreas and pleon were dissected and weighed for biochemical analysis and assessment ofdigestive enzyme activity. The remaining replicates were subjected to the same procedure at theend of the experiment (day 90). Results showed that endogenous digestive enzymes weremodulated by the multienzyme extract. Juveniles fed diet E significantly increased the specificactivity of endogenous digestive peptidases and showed a trend of increasing lipases. Themultienzyme extract also promoted lipid accumulation in hepatopancreas, increased glycogen in muscle, and reduced protein content in both tissues. These metabolic changes did not improvegrowth, as no significant differences in final weight were observed between treatments. The results highlight the need to analyze the synergy between varying concentrations of the multienzyme extract and endogenous enzymes within different protein: lipid ratios in diets, to enhancethe digestive potential of crayfish and to improve growth.