The experiment was conducted in a sealed, temperature-controlled room. The initial water temperature of the treatment group was 12°C, lowered by 1°C a day to 8°C using a chiller, and maintained at that temperature for 3 days. The water temperature was then increased by 1°C per day to 12°C using a heater. The control group were the fish that kept at 12°C at the beginning of the experiment; T1 represents the group that sampled on the first day when the water temperature reached 8 from 12°C; T2 represents the group that sampled when the fish had been kept at 8°C for 3 days; T3 represents the group sampled when the water temperature was increased to 12 from 8°C. The antioxidant abilities of the liver, muscle, and intestine of large yellow croaker at different temperatures and times were determined, and the expression of HSP70 and HSP90 in the liver as well as the changes in intestinal microbiota were investigated. The results showed that the activities of SOD, CAT, GSH-Px, and MDA content increased significantly when the water temperature decreased from 12 to 8°C, significantly higher than those in the control group. The gene expression levels of HSP70 and HSP90 in the liver of large yellow croaker significantly increased under low temperature stress and were significantly higher than those in the control group. The diversity and abundance of intestinal microbiota of large yellow croaker were altered when the water temperature was maintained at 8°C, although the change was not obvious. Proteobacteria, Firmicutes, and Bacteroidetes were the dominate phyla in both the 12 and 8°C groups, and the temperature variation did not change the functional pathways of the microbiota. In conclusion, the acute temperature variation affected the antioxidant ability and heat shock protein expression of large yellow croaker but did not affect the diversity or abundance of the intestinal microbiota. These results will provide a theoretical basis for studying the mechanisms of large yellow croaker overwintering and adaptation to low temperatures.

In this study, we determined the complete mitochondrial genome of Neolissochilus heterostomus. The genome is 16,585 bp in length, including 2 ribosomal RNA genes, 13 proteins-coding genes, 22 transfer RNA genes, and two non-coding control regions. Sequence analysis showed that the overall base composition of N. heterostomus is T 24.8%, C 27.7%, A 31.7%, and G 15.8%. The sequence is a slight A + T bias of 56.5%, which is similar to other fishes. We describe a phylogenetic analysis of 16 species of Cypriniformes based on the complete mitochondrial genome, and the result showed that N. stracheyi is most closely related to N. heterostomus. This mitogenome sequence data would play an important role in the investigation of phylogenetic relationship of the Cyprinidae.

The intestinal microbiota play a vital role in the growth and health of the host. Probiotics could influence the homeostasis of intestinal microbiota, but the relationship between species and ecosystem stability is poorly understood. Here, four diets with different doses of Bacillus cereus (control, 0 cfu/kg; BL7, 10⁷ cfu/kg; BL9, 10⁹ cfu/kg; and BL11, 10¹¹ cfu/kg) were designed to investigate the intestinal microbiota in Paramisgurnus dabryanus. The growth experiment demonstrated that the growth performance and the indices of Chao1, phylogenetic diversity, Simpson and Shannon improved significantly after loaches were fed a BL11 diet. The dominant composition of intestinal microbiota at phylum, class and genus levels did not change in loach after feeding different diets. Categories of bacterial taxa revealed that rare taxa and conditionally rare taxa were the dominant bacterial taxa in intestinal microbiota of loach. B. cereus supplemented with 10¹¹ cfu/kg promoted the stability of the ecological network of intestinal microbiota by reinforcing the cooperation of interspecific interactions, promoting operational taxonomic units to shape larger submodules and increasing module hubs species and connectors species. Results of functional prediction revealed that a total of 5692 functions were shared among the four groups, which accounted for 91.7% of overall functions. To sum up, dietary supplementation with B. cereus had no significant influences on the composition and bacterial taxa of intestinal microbiota and the composition of bacterial functions. A dose of B. cereus appropriate to the diet could improve the growth performance and promote the homeostasis of intestinal microbiota in loach.

Background: Accurate species delimitation is essential for phylogenetic, phylogeographic, ecological, conservation and biogeographic investigations. Acrossocheilus species classification has long been contentious, owing to their uncertain evolutionary relationships, high levels of morphological homoplasy and a lack of knowledge of the taxonomic validity of conventionally utilized morphological characters. Methods: A final data set consisting of 102 mitochondrial cytochrome oxidase I (COI) gene sequences was analysed for K2P intraspecific and interspecific divergence in the current study, using reconstruction methods (maximum likelihood) and various models (ABGD, PTP, GMYC) to divide the sequences according to the pattern of genetic variation. We used landmark-based geometric morphometrics to identify specimens. Result: Two taxa were identified according to the phylogenetic tree (maximum likelihood method) and three different models (ABGD, PTP, GMYC). The molecular taxonomy of Acrossocheilus agreed with the morphological identification of specimens from the same collection locality. Therefore, the COI gene and geometric morphometrics were effective in species identification of A. fasciatus.