Effects of live prey on growth performance, immune and digestive enzyme activities, and intestinal health in juvenile lined seahorse (Hippocampus erectus)

The lined seahorse ( Hippocampus erectus ), an endangered species listed under CITES Appendix II, encounters critical bottlenecks in juvenile rearing due to its agastric digestive tract, tubular snout structure, and vertical feeding posture. Identifying suitable initial live prey that meets the specific physiological needs is crucial for mitigating these challenges in juvenile seahorse aquaculture. This study systematically evaluated the effects of AN ( Artemia nauplii ), CO (copepods), and their combinations at different ratios (2:1, MX1; 1:2, MX2) on the growth performance, weaning success (WS), immune-digestive enzyme activities, and intestinal health in H. erectus . Results demonstrated that the MX2 combined diet exhibited significantly higher survival rate (82.41 %), WS (95.28 %), specific weight growth rate (SGRW, 6.27 ± 0.04 %·d −1 ), and final body weight (574.9 mg) compared to single-prey diets. Enzyme activity analysis revealed significantly enhanced antioxidant capacity (catalase (CAT), 10.91 U/mg prot) and digestive enzyme activity (protease (PG), 590.55 U/mg prot) in the MX2 group. Histological examination discerned more structurally intact intestinal tissues with increased epithelial folds in both MX1 and MX2 groups. Furthermore, villus height (171.36 μm) was notably higher in the MX2 group than in single-prey groups. The MX2 diet enriched beneficial bacteria ( Lactobacillus spp., 12.55 %), suppressed potential pathogens, and maintained higher microbial diversity and metabolic functionality. Overall, the MX2 composite diet markedly improved juvenile survival and growth performance during the early feeding stage, along with digestive capacity, while optimizing intestinal structure and microbiota composition through nutritional synergism. These findings provide novel insights into a multidimensional “nutrition-microbiota-immunity” regulatory framework for efficient H. erectus aquaculture. • Biological baits significantly affected the growth performance and weaning success rate of lined seahorse ( Hippocampus erectus ) juveniles. • Composite feeding with a 1:2 ratio of Artemia nauplii to copepods significantly enhanced digestive and antioxidant capacity in lined seahorse juveniles. • Composite feeding with a 1:2 ratio of Artemia nauplii to copepods significantly improved intestinal health in lined seahorse juveniles. • The composite biological baits comprehensively improved the health level and breeding efficiency of lined seahorse juveniles through “nutrition-microbiota-immunity”.