Effects of the Feeding Frequency of Frozen Housefly Larvae on the Growth Performance, Physiological Functions, and Intestinal Microbiota of Cherax quadricarinatus.

Optimal feeding strategies for the red claw crayfish, Cherax quadricarinatus, remain to be established. In this study, C. quadricarinatus was fed frozen housefly larva meal (Musca domestica [MD]) at different frequencies to evaluate effects on growth performance, antioxidant capacity, digestive enzyme activity, immune genes, and intestinal microbiota structure. Four feeding protocols were established: control (C) fed basic feed, experimental group 1 (E1) fed basic feed for 2 days and then compound feed (50% MD + 50% basic feed) for 1 day, experimental group 2 (E2) fed basic feed for 1 day and then compound feed for 1 day, and experimental group 3 (E3) fed compound feed daily. After 10 weeks, the weight gain rate (WGR) was significantly higher in E3 than in the other three groups (p < 0.05), while the survival rate (SR), specific growth rate (SGR), and hepatosomatic index (HSI) did not differ among groups (p > 0.05). In terms of physiological processes, lipase (LPS) and trypsin (TPS) activities were higher, expression levels of the immune-related gene lysozyme (LZM) were significantly higher, and acid phosphatase (ACP) activity was significantly higher in E2 than in the control group (p < 0.05). E2 showed the highest ecdysone receptor (EcR) and retinoid X receptor (RXR) expression levels, related to molting regulation. In the intestinal microbiota, there were no differences in α-diversity indices among groups; however, E1 increased the abundance of the phylum Bacteroidota. Consequently, while daily MD feeding (E3) maximized weight gain, intermittent feeding (E2) offered a superior balance between growth performance and physiological homeostasis, including digestion, immunity, and molting regulation. These findings provide a theoretical basis for precision farming of C. quadricarinatus.