Effects of Different Sediment Improvers on the Growth Environment, Innate Immune Responses, and Intestinal Health of Procambarus clarkii

Sediment improvers are important mediators of aquatic animals' growth performance and the surrounding environmental quality. However, the physiological responses of crayfish (<i>Procambarus clarkii</i>) to different sediment improvers remain unclear. Here, we cultivated crayfish using two chemical (potassium monopersulfate and potassium ferrate) and two biological (purple nonsulfur photosynthetic bacteria and <i>Bacillus subtilis</i>) sediment improvers at low and high concentrations. After 42 days, we found that the addition of chemical sediment improvers was more effective in improving water quality than biological sediment improvers (e.g., more stable pH and lower nutrient concentrations). By contrast, the application of biological sediment improvers resulted in considerably enhanced final weight, weight gains, and survival rates. In all low-concentration groups, the activity of immune-related enzymes (e.g., superoxide dismutase and glutathione peroxidase) in the hemolymph and hepatopancreas considerably increased, whereas the malondialdehyde activity and mRNA expression of AMP genes (<i>PcALF</i> and <i>PcCru</i>) considerably decreased. Crayfish exposed to low concentrations of sediment improvers exhibited enhanced intestinal and hepatopancreatic integrity, with a thickened mucosal layer and increased density of epithelial cell granules. Additionally, the composition of the gut microbiota varied after the addition of different sediment improvers. In summary, our research indicated that different types of sediment improvers not only improved the farming environment but also had varying effects on crayfish. Therefore, an appropriate sediment improver based on specific aquaculture conditions is needed.