Effects of varying levels of crawfish (Procambarus clarkia) shell meals on growth, fillet quality, and health of koi carp (Cyprinus carpio)

The rapidly growing of the crawfish industry generates a massive quantity of waste by-products such as heads and shells. This study evaluates crawfish shell meal (CSM) as an alternative source to fishmeal. Five isonitrogenous (crude proteins, 41%, dry matter) and isocaloric (crude lipid, 6%) experimental diets, with different levels of CSM to replace fishmeal (0%, 25%, 50%, and 75%; 75% + bile acids), were formulated to feed koi carps (4.41 +/- 0.1 g) for eight weeks. Fish that were fed 25% and 50% CSM diets exhibited no significant differences in growth performance or feed utilization (P > 0.05), whereas these indices decreased significantly in fish that were fed 75% CSM (P < 0.05). Additional supplementation with bile acids did not undo the adverse effects of CSM overdoses (P > 0.05). Dietary CSM increased the visceral, hepatopancreatic, intraperitoneal fat, and intestinal indices. In contrast, only 75% CSM caused the visceral, hepatopancreas, and intestinal indices to differ significantly (P < 0.05). Dietary bile acids almost restored these indices to their original values, with only the hepatopancreas index differing significantly (P < 0.05). Only 75% CSM significantly increased total serum protein, albumin, globulin, triglyceride, and very-low-density lipoprotein cholesterol levels compared to those in the control group (P < 0.05). Bile acids did not restore the original levels of these parameters (P > 0.05); however, they significantly restored the decreased muscle moisture induced by 75% fishmeal replacement (P < 0.05). No obvious differences were observed in the proximate, amino acid, and fatty acid compositions of the muscles among the various treatments (P > 0.05). The 75% CSM treatment significantly decreased muscle shearing force, which was recovered by bile acids (P < 0.05). No apparent differences in serum antioxidative and antibacterial enzymes, including catalase, total antioxidant capacity, superoxide dismutase, and lysozyme, were observed in the serum and liver; however, replacing 75% of fishmeal with CSM increased serum glutathione peroxidase and acid phosphatase activities (P < 0.05). This study demonstrates that up to 50% of fishmeal can be replaced by CSM and that additional supplementation with bile acids has trace positive effects during CSM oversupplementation (75% supplemented level).