Invasive species that rapidly spread throughout novel distribution ranges are prime models to investigate climate-driven phenotypic diversification on a contemporary scale. Previous studies on adaptive diversification along latitudinal gradients in fish have mainly considered body size and reported either increased or decreased body size towards higher latitudes (i.e. Bergmann’s rule). Our study is the first to investigate phenotypic divergence in multiple traits, including sexually selected traits (size and shape of the male copulatory organ, the gonopodium) of invasive Gambusia affinis in China. We studied body size, life history traits and morphological variation across populations spanning 17 degrees of latitude and 16 degrees of longitude. Even though we found phenotypic variation along climatic gradients to be strongest in naturally selected traits, some sexually selected traits also showed systematic gradual divergence. For example, males from southern populations possessed wider gonopodia with increased armament. Generally, males and females diverged in response to different components of climatic gradients (latitudinal or longitudinal variation) and in different trait suites. We discuss that not only temperature regimes, but also indirect effects of increased resource and mate competition (as a function of different extrinsic overwinter mortality rates) alter the selective landscape along climatic gradients.

Hepatic steatosis is prevalent among cultured fish, yet the molecular mechanisms remain incompletely understood. This study aimed to assess changes in hepatic metabolic function in tilapia and to explore the underlying molecular mechanisms through transcriptomic analyses. Tilapia were allocated into two groups: a normal control (Ctr)-fed group and a high-fat diet (HFD)-fed group. Serum biochemical analyses revealed that HFD feeding led to liver damage and lipid accumulation, characterized by elevated levels of glutamic-pyruvic transaminase (GPT), glutamic-oxaloacetic transaminase (GOT), triglycerides (TGs), and total cholesterol (TC). Transcriptome analysis showed that 538 genes were significantly downregulated, and 460 genes were significantly upregulated in the HFD-fed fish. Gene Ontology (GO) enrichment analysis showed that these differentially expressed genes (DEGs) were apparently involved in the lipid metabolic process and monocarboxylic acid metabolic process. Meanwhile, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis indicated significant alterations in pathways of steroid biosynthesis, porphyrin metabolism, terpenoid backbone biosynthesis, and retinol metabolism after HFD feeding. Additionally, results from Gene Set Enrichment Analysis (GSEA) revealed that gene expression patterns in pathways including oxidative phosphorylation, protein export, protein processing in the endoplasmic reticulum, and ribosome biogenesis were positively enriched in the HFD-fed tilapia. These findings provide novel insights into the mechanisms underlying HFD-induced hepatic dysfunction in fish, contributing to the optimization of feeding strategies in aquaculture.

Microorganisms, including bacteria, fungi, and protists, are key drivers in aquatic ecosystems, maintaining ecological balance and normal material circulation, playing vital roles in ecosystem functions and biogeochemical processes. To evaluate the environmental impact of different river crab polyculture practices, we set up two different river crab (Eriocheir sinensis) polyculture practices: one where river crabs were cultured with mandarin fish (Siniperca chuatsi), silver carp (Hypophthalmichthys molitrix), and freshwater fish stone moroko (Pseudorasbora parva), and another where river crabs were cultured just with mandarin fish and silver carp. These two polyculture practices were referred to as PC and MC, respectively. We analyzed the water bacterial, fungal, and protist communities in the PC and MC groups using 16S, ITS, and 18S ribosomal RNA high-throughput sequencing. We found that the PC group obviously increased the diversity of microbial communities and altered their composition. The bacterial community held the narrowest habitat niche and exhibited the weakest environmental adaption compared to fungal and protist communities. The PC group altered the co-occurrence networks of bacteria, fungi, and protist, leading to more complex and stable communities of fungi and protist. Furthermore, the PC group shifted the assembly mechanism of the bacterial community from being predominantly deterministic to predominantly stochastic processes, with relatively minor impacts on the fungal and protist communities. Environmental factors, especially dissolved oxygen (DO), were significantly associated with the communities of bacteria, fungi, and protists, with DO being the major contributor to changes in the microbial communities. Our results suggest that the polyculture of river crab with mandarin fish, silver carp, and stone moroko was an effective and viable attempt, and it was superior in terms of microbial community diversity and stability.

Hydrogen peroxide (H₂O₂), a ubiquitous reactive oxygen species in aquatic ecosystems, has been shown to induce toxicological effects in aquatic animals. However, the molecular mechanisms underlying H₂O₂-mediated alterations in muscle quality and metabolic homeostasis remain largely unexplored. In this study, we performed integrated metabolomic and transcriptomic analyses to characterize the molecular mechanisms underlying H₂O₂-induced oxidative stress in fish muscle tissue. Common carp (Cyprinus carpio) were randomized into two groups: a control group (0.0 mM H₂O₂) and an H₂O₂-treated group (1.0 mM H₂O₂) for a 14-day exposure. Following the exposure, comprehensive analyses, including fatty acid composition, amino acid profiles, and multi-omics sequencing, were conducted to elucidate the metabolic responses to oxidative stress. The results showed neither the amino acid nor the fatty acid composition exhibited significant modifications following H₂O₂ exposure. Metabolomic profiling identified 83 upregulated and 89 downregulated metabolites, predominantly comprising organic acids and derivatives, lipids and lipid-like molecules. These differential metabolites were associated with histidine and purine-derived alkaloid biosynthesis, glyoxylate and dicarboxylate metabolism pathways. Transcriptomic analysis identified 470 upregulated and 451 downregulated differentially expressed genes (DEGs). GO enrichment analysis revealed that these DEGs were significantly enriched in muscle tissue development and transcriptional regulatory activity. KEGG analysis revealed significant enrichment in oxidative phosphorylation, adipocytokine signaling, and PPAR signaling pathways. The elevated oxidative phosphorylation activity and upregulated adipocytokine/PPAR signaling pathways collectively indicate H₂O₂-induced metabolic dysregulation in carp muscle. Through the integration of metabolomics and transcriptomics, this study offers novel insights into the toxicity of H₂O₂ in aquatic environments, elucidates adaptive mechanisms of farmed fish to oxidative stress, and provides a theoretical basis for developing antioxidant strategies.