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.

Intestinal microbiota plays key roles in maintaining the health and homeostasis of the host. However, information about whether the formation of intestinal microbiota of wild aquatic animals is associated with habitat microbes is not fully understood. Here, intestine samples were collected from two wild crab species and sediment samples were collected from the habitat environment. The total DNA of each sample was extracted, and the V3–V4 regions of 16S rRNA were sequenced using the MiSeq platform. The purpose of this study was to investigate the composition and diversity of intestinal microbiota and habitat microbes, and bacterial community relationships between wild crab intestine and habitat sediment. In the present study, the composition and diversity of intestinal microbiota of the two crab species were different from the habitat microbes. In contrast, a similar composition and diversity of the intestinal microbiota were observed between two crab species. Moreover, the bacterial community relationships between crab intestine and habitat sediment were associated with intestinal regions. Further network analysis revealed that the network structure of the intestinal microbiota was not only associated with intestinal regions, but also with the crab species. Additionally, although the compositions of bacterial functions were similar between crab intestine and sediment, no significant correlation in bacterial functions was observed between crab intestine and sediment. The findings of the present study would contribute to understanding the relationship between intestinal microbiota of wild aquatic animal and habitat microbes, and providing new insights into the intestinal microbiota of wild aquatic animals.

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.

This study investigated the effects of dietary Bacillus cereus, administered alone or in combination with biofloc technology, on the growth performance, immune response, disease resistance, and intestinal microbiota of Litopenaeus vannamei. Shrimp fed diets supplemented with B. cereus, either directly or via biofloc systems, exhibited significantly increased final body weight and specific growth rate, together with a reduced feed conversion ratio compared with the control group. The expression levels of key hepatopancreatic immune-related genes, including lysozyme, prophenoloxidase, superoxide dismutase, Toll, immune deficiency, and Relish, were significantly upregulated in probiotic-associated treatments. Following challenge with Vibrio parahaemolyticus, cumulative mortality was markedly lower in all treatments involving B. cereus or biofloc compared with the control. Although alpha diversity indices were not significantly affected, beta diversity analysis demonstrated that supplementation frequency and delivery mode altered intestinal microbial community structure. The phyla Bacteroidota, Firmicutes, and Proteobacteria predominated across treatments, while members of Marinilabiliaceae and Shewanellaceae were enriched under probiotic-associated conditions, suggesting enhanced nutrient transformation potential. Co-occurrence network analysis further revealed increased microbial network complexity and positive interactions in probiotic and biofloc treatments, indicating improved community stability. These findings demonstrate that the synergistic application of B. cereus and biofloc technology enhances growth performance, immune capacity, and intestinal microbial resilience in intensive shrimp culture, and that supplementation strategy plays a critical role in optimizing probiotic efficacy.

To examine temporal patterns in the intestinal microbiota of juvenile Nibea albiflora, as well as their associations with rearing-water bacterial communities, intestinal contents and corresponding water samples were collected at 36, 46, 66, 86, and 106 days post-hatching. High-throughput 16S rRNA gene sequencing and bioinformatics analyses were used to profile community composition, structure, succession, core taxa, and their relationships with host growth and rearing water microbiota. Across all sampling points, the Chao1 index of intestinal microbiota was significantly lower, while the Shannon index was significantly higher, than those in the rearing water. In the intestine, Chao1 increased initially then stabilized, whereas Shannon declined; in rearing water, Chao1 decreased and then increased, while Shannon showed the opposite trend (P<0.05). PERMANOVA and ANOSIM analyses indicated significant temporal shifts in intestinal communities during growth and persistent differences from rearing-water microbiota (P<0.05). Dominant intestinal phyla were Bacteroidetes, Firmicutes, and Proteobacteria; Bacteroidetes increased significantly after day 46, whereas Firmicutes and Proteobacteria declined. Water microbiota was dominated by Bacteroidetes, Patescibacteria, and Proteobacteria, with the first two phyla increasing and Proteobacteria decreasing over time. At the family level, intestinal communities were enriched in Lachnospiraceae, Muribaculaceae, Prevotellaceae, and Streptococcaceae; the first three families declined significantly after day 46, while Muribaculaceae increased. Water communities were dominated by Clade_I, Flavobacteriaceae, and Rhodobacteraceae, with Clade_I decreasing and the latter two showing a rise-then-fall pattern. Procrustes and source-tracking analyses revealed no significant correlation between intestinal and water communities (P>0.05). Habitat-specificity analysis, random forest modeling, and Mantel tests identified key taxa associated with juvenile growth, and two potentially autochthonous probiotic strains were successfully isolated from the intestine. These findings characterize the temporal dynamics and functional taxa of the intestinal microbiota in juvenile N. albiflora and their relationship to rearing-water communities, providing a foundation for developing host-specific probiotics in this species.