Diversity of life history and population connectivity of threadfin fish Eleutheronema tetradactylum along the coastal waters of Southern China

Metabolomics-Based Analysis of Adaptive Mechanism of Eleutheronema tetradactylum to Low-Temperature Stress

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.

Molecular Modulation of Threadfin Fish Brain to Hypoxia Challenge and Recovery Revealed by Multi-Omics Profiling

Migratory fish often encounter hypoxic zones during migration, which can lead to varying degrees of hypoxic stress. This issue has become increasingly severe due to human activities and climate change, which have resulted in the expansion of hypoxic zones in aquatic environments. However, there is limited research on how these species respond to hypoxic stress and subsequent recovery. In this study, we used Eleutheronema tetradactylum, a well-recognized migratory and economically valuable fish species, as a model organism. Histological analysis revealed extensive neuronal damage during hypoxia exposure, with limited recovery observed even after 12 h of reoxygenation. Differential gene expression analysis highlighted progressive alterations in genes associated with stress response, neuroactive ligand interactions, and cellular repair mechanisms. Time-series analysis of differentially expressed genes (DEGs) identified critical expression profiles throughout the hypoxia-recovery process and revealed hub genes for each stage. Furthermore, dynamic changes in miRNA expression and proteomic profiles indicated active regulation of several key biological pathways, including MAPK, HIF-1, and ECM-receptor interactions. Through miRNA-mRNA-protein correlation analysis, we propose a model that predicts key regulatory pathways and critical miRNA-mRNA-protein interactions across the various stages of hypoxia-recovery in the brain of E. tetradactylum. This study presents the first integrated analysis of miRNA, mRNA, and protein throughout the entire hypoxia-recovery process in fish brains. The molecular interactions and regulatory pathways identified in this model could serve as valuable biomarkers for future research on hypoxia-recovery mechanisms in fish.

Effects of Bacillus coagulans on Growth Performance, Digestive Enzyme Activity, and Intestinal Microbiota of the Juvenile Fourfinger Threadfin (Eleutheronema tetradactylum)

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.

Quantifying larval dispersal portfolio in seabass nurseries using otolith chemical signatures

The temporal asynchronies in larvae production from different spawning areas are fundamental components for ensuring stability and resilience of marine metapopulations. Such a concept, named portfolio effect, supposes that diversifying larval dispersal histories should minimize the risk of recruitment failure by increasing the probability that at least some larvae successfully settle in nursery. Here, we used a reconstructive approach based on otolith chemistry to quantify the larval dispersal portfolio of the European seabass, Dicentrarchus labrax, across six estuarine nursery areas of the northeast Atlantic Ocean. The analysis of natal and trajectory signatures indicated that larvae hatch in distinct environments and then dispersed in water masses featured by contrasting chemical signatures. While some trace elements appeared affected by temporal changes (Mn and Sr), others varied spatially during the larval stage but remained poorly affected by temporal fluctuation and fish physiology (Ba, Cu, Rb and Zn). We then proposed two diversity metrics based on richness and variations of chemical signatures among populations to reflect spatio-temporal diversity in natal origins and larval trajectories (i.e., estimates of dispersal portfolio). Along the French coast, the diversity estimates were maximum in nurseries located at proximity of offshore spawning sites and featured by complex offshore hydrodynamic contexts, such as the Mont St-Michel bay. Finally, our findings indicate that the dispersal portfolio was positively related with the local abundance of seabass juveniles, supporting the assumption that heterogeneity in dispersal history contributes to promote recruitment success in nurseries.

Seascapes Shaped the Local Adaptation and Population Structure of South China Coast Yellowfin Seabream (Acanthopagrus latus)

Understanding the genetic composition and regional adaptation of marine species under environmental heterogeneity and fishing pressure is crucial for responsible management. In order to understand the genetic diversity and adaptability of yellowfin seabream (Acanthopagrus latus) along southern China coast, this study was conducted a seascape genome analysis on yellowfin seabream from the ecologically diverse coast, spanning over 1600 km. A total of 92 yellowfin seabream individuals from 15 sites were performed whole-genome resequencing, and 4,383,564 high-quality single nucleotide polymorphisms (SNPs) were called. By conducting a genotype-environment association analysis, 29,951 adaptive and 4,328,299 neutral SNPs were identified. The yellowfin seabream exhibited two distinct population structures, despite high gene flow between sites. The seascape genome analysis revealed that genetic structure was influenced by a variety of factors including salinity gradients, habitat distance, and ocean currents. The frequency of allelic variation at the candidate loci changed with the salinity gradient. Annotation of these loci revealed that most of the genes are associated with osmoregulation, such as kcnab2a, kcnk5a, and slc47a1. These genes are significantly enriched in pathways associated with ion transport including G protein-coupled receptor activity, transmembrane signaling receptor activity, and transporter activity. Overall, our findings provide insights into how seascape heterogeneity affects adaptive evolution, while providing important information for regional management in yellowfin seabream populations.