Abstract
Given the economic significance of Procambarus clarkii in freshwater aquaculture and the lack of microbial antioxidants in Procambarus clarkii diet research, this study aimed to investigate the optimal supplementation level and feeding duration of microbial antioxidants in Procambarus clarkii diets. A series of three experiments were conducted to assess the long-term effects of different MA levels on crayfish and evaluate the palatability of the diets by observing feeding behavior and examining the short-term effects of high levels of MA. Our results indicate that long-term feeding using 1.5% MAs markedly increased the activities of antioxidant enzymes (T-AOC, T-SOD, and GSH-PX) and decreased the malondialdehyde (MDA) content in the hepatopancreas and hemolymph, with the crayfish showing significantly higher survival rates due to better antioxidant capacity after 24 h of air exposure stress. Under the condition of long-term feeding, the appropriate level of addition of MAs that can promote the growth of crayfish is 0.62-0.66%. The feeding behavior results indicate that the lower willingness and food intake of the crayfish in the high MA group may be the main reason affecting their growth. Conversely, short-term feeding using MAs alleviated the adverse effects on growth associated with the reduced palatability of the diet. The results indicate that the inclusion of 1.5% MAs in the diet for a period of 21 d optimized crayfish growth, accompanied by an improvement in antioxidant capacity and survival during transportation. This study demonstrates that diets supplemented with microbial antioxidants (MAs) can improve growth performance, antioxidant capacity, and resistance to air exposure stress in Procambarus clarkii. These results provide valuable insights into the potential benefits of MA supplementation in crayfish aquaculture.