Effects of dietary oregano essential oil on digestive tissue structure and function, antioxidant and immune responses and gut microbiota of red swamp crayfish (Procambarus clarkii)

Abstract

Modifying the diet is an effective strategy to enhance the production and health of farmed red swamp crayfish (Procambarus clarkii). In this study the effects of adding dietary oregano essential oil (OEO) at 0, 100, 300, and 500 mg/kg concentrations were investigated in red swamp crayfish after a 3-week feeding trial. Histology showed no negative impacts on the structural integrity of the hepatopancreas and intestine. Total protease activity in the hepatopancreas, hemolymph alkaline and acid phosphatase activity, hemolymph superoxide dismutase activity and hepatopancreas glutathione levels were higher in the 500 mg/kg OEO group than in the 0 mg/kg group. No significant differences were observed in hepatopancreas phenoloxidase activity or hemolymph malondialdehyde content between treatment groups. Supplementing the diet with OEO upregulated the expression of antioxidant and immune-related genes in the hepatopancreas including metallothionein, gamma interferon-inducible lysosomal thiol reductase, and catalase in the 500 mg/kg OEO group relative to the 0 mg/kg control. Ferritin gene expression was unaltered. The intestinal microbiota of crayfish fed OEO showed an increased relative abundance of Proteobacteria and Actinobacteriota, and a lower abundance of Firmicutes. This study demonstrates the potential of OEO as a novel feed additive for enhancing antioxidant capacity and the immune response in red swamp crayfish. This research addresses the growing need for sustainable aquaculture practices and highlights the application of plant-derived bioactivities in improving crustacean health.