The fish-gut microbiota play a key role in the physiology, development, and fitness of its host. An understanding of fish-gut microbial communities and the factors influencing community composition is crucial for improving fish performance. In this study, we compared the gut microbiota of juvenile black sea bream Acanthopagrus schlegelii among habitats: (1) wild, (2) offshore cage-culture, and (3) pond-culture. We also explored the relationships between the gut microbiota and host-associated environmental factors. Gut samples and associated environmental compartments were investigated using 16S rRNA gene sequencing. Our results revealed significant habitat-specific differences among the gut microbiota of juvenile A. schlegelii. Wild populations of juvenile A. schlegelii had more diverse gut microbiota than populations cultured in pond habitats due to their omnivorous feeding habits and the corresponding abundance of natural food resources. Significant variations in the composition, core taxa, and diversity of the microbiota were also found between the gut and the environmental compartments. However, no significant differences were observed among the microbiota of the environmental compartments in the relatively isolated pond habitat. Source tracking analysis recovered connections between the fish-gut microbiota and the diet, water and sediment environmental compartments. This connection was especially strong between the microbiota of the fish gut and that of the diet in the pond habitat: the diet microbiota accounted for 33.48 ± 0.21% of the gut microbiota. Results suggested that all A. schlegelii shared a core gut microbiota, regardless of differences in diet and habitat. However, environmental factors associated with both diet and habitat contributed to the significant differences between the gut microbiota of fish living in different habitats. To the authors’ knowledge, this study presents the first comparison of gut microbiota among juvenile A. schlegelii with different diets and habitats. These findings enrich our understanding of the gut microbiota of A. schlegelii and help to clarify the interaction between gut microbiota and environmental factors. Our results may also help to guide and improve fish ecological fitness via the regulation of gut microbiota, thereby increasing the efficacy of stock enhancement programs for this species.

Pampus chinensis is a commercially important fishery species in the Indo-West Pacific region. In the present study, the genetic variation of P. chinensis among 10 sampling localities along the China coast and one from the Indonesia region was evaluated using mitochondrial DNA control region sequences. As a result, a total of 30 variable sites were detected in the 458 bp segment of the control region among 330 individuals from 11 localities, and 41 haplotypes were defined. Samples in the China coast present a high level of genetic diversity, with the values of haplotype diversity ranged from 0.674 to 0.860, and nucleotide diversity from 0.820% to 1.502%. Pairwise F_ST statistics showed a moderate genetic divergence (−0.027 to 0.384) among samples from different geographical locations. Median-joining network analysis revealed a similar pattern of phylogeographic structure in samples from Ningbo and Dongxing although they were far apart. Therefore, joint influences of dispersal capability, spatial distance, ocean current and geographic segregation on the formation of the present population structure in P. chinensis was proposed. The results of the present study would be helpful for the sustainable utilization and management of this species.

The Chinese pomfret Pampus chinensis is one of the most economic and ecological important marine fish species in China. In the present study, the population genetic structure and genetic diversity of P. chinensis were evaluated from a total sample size of 180 individuals representing six populations from the East China Sea and the South China Sea using mitochondrial cytochrome c oxidase subunit I (COI) gene. A total of 24 variable sites (including 3 singleton sites and 21 parsimony information sites) were observed, and 18 haplotypes were defined. The haplotype diversity (Hd) of the populations ranged from 0.559 to 0.775, and the nucleotide diversity (π) ranged from 0.330 to 1.090%. Analysis of molecular variance (AMOVA) reveals that the main variation (66.02%) was among individuals within populations. The average pairwise differences and ϕ_ST values indicated significant genetic differentiation between Dongxing population and the other populations. The results of the present study are helpful for the sustainable management and utilization of this species.