Effects of feeding different baits on the growth of Scylla paramamosain megalopa and the bacterial community in a mariculture system.

Bait feeding plays a pivotal role in the artificial nursery process, as different baits can significantly influence water quality and microbial community structure, thereby directly affecting the growth and development of cultured organisms. In this study, four types of baits, including live Artemia nauplii (AN), frozen copepods (FC), frozen Artemia nauplii (FA), and formulated diet (FD) were used to feed megalopa-stage mud crabs (Scylla paramamosain) until their metamorphosis into the first juveniles. The effects on water quality, microbial community structure, metamorphosis survival rate, and molting duration were statistically analyzed. Results indicated that the AN group had 88 unique bacteria OTUs, followed by 80, 64 and 27 unique OTUs in the FA, FD and FC groups, respectively. Proteobacteria predominated in both AN and FA groups, while Bacteroidetes demonstrated the highest percentage in the FC and FD groups. Actinobacteria maintained consistently low relative abundance in all treatments. The FA group exhibited the highest Chao1, ACE and observed richness indices (P > 0.05), suggesting the greatest bacterial community richness. The AN group displayed the highest Pielou's evenness and Shannon index, along with the lowest Simpson' index (D) (P < 0.05), indicating a more uniform species distribution and higher community diversity. In addition, the AN group exhibited the lowest concentrations of ammonia nitrogen and nitrite among the four treatments. Moreover, the AN group showed the highest abundance of the beneficial genus Marivita, whereas the FD, FC, and FA groups had a significant increase in the harmful genus Tenacibaculum. Compared with those in the FA, FC and FD groups, the megalopae in the AN group also demonstrated the highest metamorphosis survival rate and the shorter molting duration, underscoring the critical role of live Artemia nauplii in improving water quality, and stabilizing microbial communities. These findings suggested that live Artemia nauplii were the optimal feed choice for enhancing the success of S. paramamosain megalopa breeding. Future studies could explore the integration of appending probiotics and periodic removal of harmful bacteria in the aquaculture water to further optimize microbial structure, thereby improving the metamorphosis survival rate of S. paramamosain megalopa. Moreover, strategies such as partial substitution of live Artemia nauplii with frozen Artemia could be investigated to reduce seedling cultivation costs and advance S. paramamosain aquaculture technology in the further research.