Rhodotorula mucilaginosa Supplementation Could Significantly Affect the Growth Performance, Digestive Enzyme Activity, Antioxidant Capacity, Immune Function, and Intestinal Health in Red Claw Crayfish (Cherax quadricarinatus)

This study investigated the effects of dietary <i>Rhodotorula mucilaginosa</i> supplementation with different concentrations (0.0 g/kg, 0.1 g/kg, 1.0 g/kg, 10.0 g/kg) on red claw crayfish (<i>Cherax quadricarinatus</i>). Four groups were established: control group (CK, 0.0 g/kg), low-dose group (HL, 0.1 g/kg), medium-dose group (HM, 1.0 g/kg), and high-dose group (HH, 10.0 g/kg). The feeding trial lasted for 56 days. The results showed that, compared with the control group, all supplementation groups exhibited significantly reduced feed conversion ratios (<i>p</i> < 0.05). The HM and HH groups demonstrated significant increases in body length growth rate, specific growth rate, weight gain rate, hepatosomatic index, and survival rate (<i>p</i> < 0.05). All supplemented groups showed significantly enhanced trypsin and lipase activities in intestines and trypsin activity in the hepatopancreas (<i>p</i> < 0.05). The HM and HH groups exhibited elevated α-amylase activity in the hepatopancreas (<i>p</i> < 0.05). Compared with the control group, marine red yeast supplementation reduced colonization of potential pathogens while increasing probiotic abundance, effectively improving intestinal microbiota structure. The HM group significantly improved intestinal villus length, width, and muscular thickness (<i>p</i> < 0.05). All supplemented groups showed considerable upregulation of hepatopancreatic genes related to immunity (heat shock protein 70, down syndrome cell adhesion molecule, crustacean antibacterial peptide, serine proteinase inhibitors, crustacean hyperglycemic hormone, anti-lipopolysaccharide factor, lysozyme, and alkaline phosphatase) and antioxidant defense (superoxide dismutase, glutathione peroxidase, glutathione, and catalase) (<i>p</i> < 0.05). These findings indicate that <i>R. mucilaginosa</i> can significantly enhance digestive enzyme activity, maintain intestinal health, improve antioxidant and immune-related gene expression, and promote growth performance in red claw crayfish, with the HM group (1.0 g/kg <i>R. mucilaginosa</i>) showing optimal promotion effects.