17α-Methyltestosterone Affected Growth, Gonadal Development, and Intestinal Microbial Analysis in the Giant Freshwater Prawn (Macrobrachium rosenbergii)

17α-methyltestosterone (MT) is known for its ability to suppress ovaries and induce spermatogenesis; yet, its effects in crustaceans are underexplored. This study investigates the impact of varying MT concentrations on the gonadal development and intestinal microbiota of juvenile <i>Macrobrachium rosenbergii</i>. Feeds containing different MT doses were provided, and the sex ratios, histological observations, reproductive gene expression, and intestinal microbial composition were analyzed. The results revealed short-term feeding (60 days) of 1000 mg/kg MT resulted in the highest male ratio, while long-term feeding (150 days) of 500 mg/kg MT achieved the same outcome. Conversely, long-term feeding of 1500 mg/kg MT led to the lowest male ratio and retarded male germ cell development. An intestinal microbiota analysis showed that MT supplementation significantly increased microbial abundance and altered the intestinal microbial community structure. Additionally, MT suppressed the expression of female reproductive-related genes. This study provides insights into the effects of MT on reproductive development and gut microbiota in juvenile prawns, offering a valuable reference for the application of MT in crustacean aquaculture.