The effects of dietary Cordyceps militaris substrate on growth, immunity, gonadal quality, and gut microbiota of the sea urchin Strongylocentrotus intermedius

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Abstract

Sea urchin Strongylocentrotus intermedius is a commercially valuable marine species in China. Cordyceps militaris culture (CMC), containing cordycepin, polysaccharides, cordycepic acid, amino acids, trace elements, and vitamins, was tested in varying concentrations (0.5 %, 1.0 %, and 1.5 %) in sea urchin feed to evaluate effects on growth, immunity, gonadal quality, and gut microbiota. Five groups were established: a kelp group, a control group (basic feed), and three feed groups with CMC supplementation for two months. The addition of CMC had no significant effect on survival rate. The weight gain rate in the 0.5 % CMC group was similar to the 1.0 % CMC group but lower than the kelp group. The 0.5 % CMC group had the highest gonad wet weight, comparable to the 1.0 % CMC group, and its gonad index was significantly higher than the kelp and control groups (P < 0.05). In gonad texture, the 0.5 % CMC group showed the highest hardness (not significantly different from 1.0 % CMC), significantly higher springiness, adhesiveness, and chewiness compared to the control group (P < 0.05). Cohesiveness was significantly higher than in the control group (P < 0.05), with no differences among other groups. Brightness in the 0.5 % CMC group was significantly higher than in the kelp group, while redness and yellowness were significantly lower (P < 0.05). CMC significantly enhanced SOD, CAT, and POD activities, with the 0.5 % CMC group showing higher SOD activity than the kelp, control, and 1.5 % CMC groups (P < 0.05). POD and CAT activities in the 0.5 % group were significantly higher than in the control group (P < 0.05). The 0.5 % CMC group exhibited the highest Firmicutes abundance and significantly improved gut microbiota diversity (P < 0.05). In conclusion, added 0.5–1.0 % CMC improved growth, immunity, gonadal quality, and gut microbiota. While 0.5 % CMC showed consistent improvements, some parameters reached peak values at 1.0 %.