High feeding level alters physiological status but does not improve feed conversion efficiency and growth performance of juvenile red swamp crayfish Procambarus clarkii (Girard, 1852)

Abstract

Red swamp crayfish, Procambarus clarkii (Girard, 1852), aquaculture has developed rapidly in recent years. However, limited knowledge about the response of physiological processes to different feeding levels has hindered the expansion of scientific feeding strategies. The present study was conducted to evaluate the growth performance (specific growth rate: SGRw, survival, and moulting frequency), feed utilisation (feeding rates, feed conversion ratio: FCR, waste production ratio: WPR), and physiological response variables to different feeding levels (1%, 2%, 3%, 4%, 5%, and 6% body weight per day, BW day−1) of juvenile P. clarkii for 60 days. Each treatment was replicated ten times, with 40 juveniles per treatment. No significant differences were observed in the growth performance of P. clarkii fed at 3%, 4%, 5%, and 6% BW day−1. However, they exhibited a significantly higher feeding rate, and FCR and WPR values when fed at 6% BW day−1. Among the physiological variables, activities of digestive enzymes (trypsin, lipase, and AKP) and antioxidant enzymes (SOD, CAT, and MDA) were significantly correlated with feeding levels; the Pearson correlation coefficients of these enzymes were 0.82, 0.57, 0.39, 0.66, 0.70, and −0.38, respectively. The biochemical indicators of nutrient status (total protein, total cholesterol, triglyceride, and GOT and PK activities) increased with increasing feeding levels, as revealed by the Self-Organizing Map. The two-way ANOVA revealed that P. clarkii fed at 5% and 6% BW day−1 had significantly higher trypsin and PK activities, and total protein and total cholesterol contents, whereas when fed at 6% BW day−1, it was exposed to oxidative stress. When the physiological variables were grouped by principal component analysis (PCA), they varied over experimental dates. P. clarkii exhibited higher trypsin, lipase, and MDA activities on the 20th day, but lower triglyceride content and GOT activity than on the 40th day. This study indicated that P. clarkii did not benefit from high feeding level (6% BW day−1), providing an incentive for farmers to reduce dietary input and production costs, thus promoting the sustainability of P. clarkii aquaculture.