Supplementation with Enterococcus faecium enhances growth performance, intestinal health and immunity of big-belly seahorses (Hippocampus abdominalis) during diet conversion

Diet conversion is a key stage of seahorse aquaculture. Herein, we set up five groups to evaluate the probiotic effects of Enterococcus faecium supplementation on the growth, development, intestinal health, and immunity of big-belly seahorses (Hippocampus abdominalis) during this stage, including control (C) (no E. faecium), H2 (1 ×107 CFU mL−1, every 2 d), H4 (1 ×107 CFU mL−1, every 4 d), L2 (1 ×105 CFU mL−1, every 2 d), and L4 (1 × 105 CFU mL−1, every 4 d) groups. After 48 d culture, concentration and frequency of E. faecium supplementation, as well as their interaction, were confirmed to have significant effects on growth performance of seahorses (P < 0.05). Body weight, specific growth rate, body weight increase, standard length and standard length increase of H4 and L4 groups were significantly higher (P < 0.05); Ovary weight but not testis weight and brood pouch length significantly increased in H4 group (P