Effects of dietary methyl farnesoate on growth and ovarian development of Macrobrachium rosenbergii and underlying mechanisms

Macrobrachium rosenbergii is an economically important aquaculture species worldwide, but its reproductive efficiency is severely constrained by challenges in ovarian maturation. Methyl farnesoate (MF), a sesquiterpenoid hormone, plays a critical regulatory role in crustacean reproductive development. In this study, juvenile M. rosenbergii with an average body weight of ∼4.2 g were fed diets supplemented with different concentrations of MF (0, 3, 6, and 9 μg/g) for 56 consecutive days. The effects on growth performance, ovarian development, gut microbial composition, and related gene expression were systematically evaluated. The results showed that high-dose MF (9 μg/g) significantly promoted ovarian development, accelerated the transition of oocytes from the Oc2 to Oc4 stage, and markedly increased oocyte diameter. Hemolymph vitellogenin levels were significantly elevated during days 28–42. Concurrently, MF at high doses significantly upregulated the expression of Met, Kr-h1, and Vtg, suggesting that MF may facilitate vitellogenesis via the Met–Kr-h1–Vtg signaling pathway. Gut microbiota analysis revealed that MF reshaped microbial community structure, with the highest diversity observed in the 9 μg/g group, and dominant genera shifted to Enterobacter and Clostridium, potentially enhancing immune and metabolic capacity. In contrast, low-dose MF (3 μg/g) exhibited inhibitory effects on both growth and ovarian development. In summary, this study systematically elucidates the dose-dependent effects of MF on ovarian maturation in M. rosenbergii and reveals potential molecular mechanisms, providing a theoretical basis for efficient crustacean breeding and hormone-replacement strategies.