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

One of the challenges in aquaculture is reducing the use of fishmeal to alleviate pressure on aquatic ecosystems while maintaining protein quality and digestibility. A promising approach is the supplementation of diets with exogenous enzymes, a strategy widely used in aquaculture nutrition but scarcely explored in crustaceans. This study aimed to evaluate the effects of a diet composed 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 digestive enzyme activities, and biochemical reserves (proteins, lipids, and glycogen) in hepatopancreas and pleon muscle were analyzed. Sixty-two crayfish weighting ⁓1.5 g were assigned to one of the following 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 their body 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 of digestive enzyme activity. The remaining replicates were subjected to the same procedure at the end of the experiment (day 90). Results showed that endogenous digestive enzymes were modulated by the multienzyme extract. Juveniles fed diet E significantly increased the specific activity of endogenous digestive peptidases and showed a trend of increasing lipases. The multienzyme extract also promoted lipid accumulation in hepatopancreas, increased glycogen in muscle, and reduced protein content in both tissues. These metabolic changes did not improve growth, 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 enhance the digestive potential of crayfish and to improve growth.