Effects of feed protein levels on Chinese mitten crabs (Eriocheir sinensis) under the rice-crab co-culture model: Performance, nutrient composition, antioxidant capacity and immunity

The Chinese mitten crab is an important aquaculture product in China. Currently, rice-crab co-culture is a novel model that can realize positive interactions. The feed for Chinese mitten crabs cultured in rice fields should be distinguished from other modes, since their culture environment is unique. Therefore, this study designed three experimental groups that were fed 15% (RC1), 25% (RC2), and 35% (RC3) protein, with a natural bait group (RC0) without artificial feeding as the control. The protein nutritional requirements of Chinese mitten crabs in a rice-crab co-culture model were investigated by exploring the indicators of growth performance, nutrient composition, immunity, antioxidant capacity, and economic benefits of different groups. Through a comprehensive discussion of one-way analysis of variance and regression analysis of the data, we obtained the following results: feeds with high-level protein improved the growth performance, quality, and economic benefits of Chinese mitten crabs and reduced their exposure to oxidative stress. Specifically, the contents of major nutrients and flavor-presenting substances, such as free amino acids (FAA), nucleotides, and essential amino acids (EAA), in the edible parts of female crabs in the 35% protein group were significantly higher than those in all other groups. Male crabs fed 25% − 28.08% protein diets showed higher production performance and FAA content. In conclusion, the optimal dietary protein levels for male and female crabs reared in rice fields are different: they are 35% for females, and at least 25% for males. Therefore, for actual crab production, male and female crabs could be cultured separately using different protein baits to reduce bait costs and achieve green and sustainable development.