Hui Zhou

The molecular coordination between the central nervous system and peripheral organs is fundamental to euryhalinity. This study elucidates the distinct adaptive strategies of the brain and gills in the four-finger threadfin (Eleutheronema tetradactylum), an aquaculture species of growing importance, during long-term (30-day) acclimation to low salinity (5 versus 25 control). A profound dichotomy in tissue-specific plasticity was uncovered: while the brain maintained remarkable transcriptional stability with only 10 differentially expressed genes (DEGs), the gills underwent extensive remodeling with 702 DEGs. Gill DEGs were functionally enriched in ion transport and metabolic remodeling, highlighted by the significant upregulation of the Na⁺-Cl⁻ cotransporter (slc12a10) and the prolactin receptor (prlr), coupled with a profound downregulation (log₂FC = −5.97) of aquaporin-1 (aqp1). This indicates a concerted strategy to enhance ion uptake while minimizing water permeability. In contrast, the brain’s subtle response was dominated by the upregulation of key neuroendocrine hormones, including growth hormone (gh), prolactin (prl), and pro-opiomelanocortin (pomc). This suggests a top-down regulatory cascade. Integrative pathway analysis identified the PI3K-Akt and JAK-STAT signaling pathways as the primary conduits linking central hormonal signals to peripheral physiological adjustments. These results demonstrate that the euryhalinity of E. tetradactylum is achieved through a highly efficient strategy: a transcriptionally stable brain provides precise endocrine commands that orchestrate robust peripheral remodeling in the gills. This study deciphers the molecular basis of the brain–gill axis in osmoregulation and provides a rich repository of candidate genes for the genetic improvement of low salinity tolerance in aquaculture.

Temperature is a critical environmental factor that influences the growth, development, metabolism, and overall physiological performance of fish. Eleutheronema tetradactylum is an economically significant fish species; however, its molecular mechanism’s response to long-term cold stress is still unclear. In this study, we investigated the physiological responses of the liver in E. tetradactylum exposed to a constant temperature of 18 °C for durations of both 7 and 14 days, utilizing liquid chromatography–mass spectrometry (LC-MS), metabolomics, and conventional biochemical assays. The antioxidant status, liver histology, and metabolite profiles were examined at different time points. Our results revealed that, following sustained cold exposure, the activities of key antioxidant enzymes—superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx)—initially increased and then decreased. Additionally, levels of malondialdehyde (MDA), a marker of oxidative damage, significantly elevated after 7 and 14 days of cold stress. Histopathological examination of liver tissues showed varying degrees of vacuolation and nuclear atrophy in hepatocytes, indicating oxidative damage. Metabolomic profiling identified 87 and 116 differentially expressed metabolites in the liver on days 7 and 14, respectively. Pathway enrichment analysis revealed significant alterations in pathways related to carbohydrate digestion and absorption, glutathione metabolism, and glycerolipid metabolism. These findings suggest that mechanisms regulating cell membrane fluidity, energy metabolism, autophagy, and antioxidant defense are crucial for the adaptation of E. tetradactylum to cold stress. Overall, this study provides valuable insights into the molecular and physiological adaptations of E. tetradactylum to low temperature, highlighting the activation of protective antioxidant responses and modifications of metabolic pathways in the liver.

The Integrated Multi-Trophic Aquaculture (IMTA) model is an eco-friendly aquaculture system that enhances water purification through ecological niche utilization. A study employing 16S rRNA sequencing analyzed microbial communities in aquaculture water at initial, middle, and final stages. Results indicated that physicochemical parameters were lower at the final stage. The removal efficiencies of Total Nitrogen (TN) and Total Phosphorus (TP) reached 79.10% and 63.64%, respectively. The Simpson and Shannon indices revealed that microbial diversity was significantly higher in the final stage compared to the initial and middle stages (p < 0.05). Dominant bacterial phyla included Actinobacteria, Proteobacteria, and Bacteroidetes, while dominant genera included Candidatus_Aquiluna, NS3a_marine_group, and NS5_marine_group. Functional prediction results demonstrated that metabolic pathways such as amino acid metabolism, biosynthesis of other amino acids, and energy metabolism were upregulated in the final stage compared to the initial stage. Correlation analysis of environmental factors suggested that TN and TP significantly influenced the microbial community structure. Key microorganisms such as Candidatus_Aquiluna, Marinomonas, and Cobetia played crucial roles in carbon fixation, nitrogen reduction, and phosphorus removal. In summary, the IMTA model effectively purifies water, with microbial communities contributing to the stability of the aquatic environment.

The effects of Bacillus coagulans (BC) T-21 on growth performance, intestinal digestive enzyme activity, intestinal morphology, and intestinal microbiota of juvenile fourfinger threadfin (Eleutheronema tetradactylum) were investigated in the present study. Healthy juvenile E. tetradactylum with an initial body weight of 4.2 ± 0.5 g were fed a basal diet sprayed with 1 × 10⁸ cfu/g B. coagulans for eight weeks, and the growth parameters, intestinal digestive enzyme activities, HE-stained intestinal sections, and intestinal microbiota of the juvenile fish were measured. The differences in the feed conversion ratio between the experimental and control groups (fed the basal diet) were extremely significant (p < 0.01), whereas the differences in weight gain rate, specific growth rate, survival rate, and condition factor were significant (p < 0.05). In the experimental group, trypsin and amylase activities decreased significantly, whereas there were no significant differences in lipase activity between the two groups. Compared to the control group, the height of the intestinal villi was greater. No significant differences were observed in the diversity of intestinal microbiota and microbial species at the genus level (p > 0.05). Based on the function prediction analysis, the count values for the glycan biosynthesis, metabolism, and digestive system pathways were significantly increased in the experimental group (p < 0.05). However, there were no significant differences in the counts of other functional pathways (p > 0.05). These results indicate that dietary B. coagulans supplementation is effective in promoting the growth performance and intestinal health of juvenile E. tetradactylum.