Teleosts are the most varied vertebrates. They inhabit various environments and are crucial to global fisheries, making them a focus of research using advanced omics approaches. These studies provide insights into the genetic factors, environmental adaptability, disease resistance, and metabolic processes, aiding aquaculture sustainability. Acclimation to salinity stress is complex, influenced by genetics and the environment. Although some species tolerate varying salinity levels, rapid shifts beyond their optimal tolerance cause stress. Euryhaline species experience stress at extreme salinities, whereas stenohaline species are sensitive to minor changes. Osmoregulation maintains homeostasis at varying salinities through acclimation in the intestine, kidney, and gills, ensuring survival in changing environments. Studies on gut microbiota and metabolomics have revealed how teleosts cope with salinity stress. This review delves into the acclimatization processes through transcriptomic, metabolomic, and gut microbiome analyses, which have shed light on the complex mechanisms that teleosts have evolved to cope with salinity stress. Transcriptomic analyses have identified key ion transport, osmoregulation, and stress response genes essential for adaptation, facilitating cellular adjustments and maintaining osmotic balance across habitats. Studies have revealed significant metabolite changes in energy production and osmolyte synthesis during stress, indicating metabolic reorganization for osmoregulation. Gut microbiota analysis highlights microbial diversity in regulating osmoregulatory functions, emphasizing microbiota’s role in resilience. Although research on interactions between salinity, growth conditions, and gut microbiota in teleosts is limited, findings suggest a vital relationship that warrants further study. Understanding these mechanisms is essential for improving fish health and enabling sustainable aquaculture management under environmental fluctuations.

Introduction: This study investigates the effects of salinity on the growth, survival, tissue morphology, osmotic regulation, metabolism, and antioxidant responses of juvenile Eleutheronema tetradactylum.Methods: The experiment was conducted under controlled aquaculture conditions with eight salinity treatments (0, 5, 10, 15, 20, 25, 30, and 35 PSU), each with three replicates (20 fish per replicate) in cylindrical tanks (500 L). Juveniles (mean total length: 16.43 ± 0.87 cm; mean body weight: 35.71 ± 1.067g) were exposed to the treatments for 30 days. Key measurements included plasma osmotic pressure, ion concentrations, and Na+/K+-ATPase (NKA) in the gills, assessed at 0, 1, 10, 20, and 30 days.Results: Survival rates, growth parameters, and histopathological changes in gill, intestinal, and kidney tissues were also evaluated. Additionally, plasma levels of lactic acid (LD), triglycerides (TG), glucose (GLU), total superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), total antioxidant capacity (T-AOC), and malondialdehyde (MDA) were measured. The results revealed that survival rates were significantly lower in the 0 PSU group compared to all other salinities (P< 0.05). Growth performance, including specific growth rate (SGR), weight gain rate (WGR), and daily weight gain (DWG), was significantly reduced at high salinities (30 and 35 PSU) (P< 0.05). Histopathological alterations were observed in the gills, intestine, and kidneys, particularly in osmoregulatory tissues. Salinity also significantly affected NKA, plasma osmotic pressure, and ion concentrations. The isosmotic point for E. tetradactylum was determined to be approximately 10.88 PSU. Metabolic responses, including LD, TG, and GLU, exhibited a pattern of initial decline followed by an increase with increasing salinity. SOD activity was significantly higher in the 10 PSU group compared to the 30 and 35 PSU groups (P< 0.05), while T-AOC showed a “U”-shaped response to increasing salinity. GSH-Px activity decreased with salinity, especially at 35 PSU (P< 0.05), while MDA levels did not vary significantly (P > 0.05).Discussion: In conclusion, E. tetradactylum belongs to euryhaline fish species, with optimal growth occurring at lower salinities(5-10PSU). High salinity (30–35 PSU) adversely affects growth and antioxidant defense mechanisms, highlighting the species’ sensitivity to elevated salinity. Beyond identifying species-specific sensitivity, this work provides actionable guidelines for optimizing aquaculture practices, reducing metabolic costs, and mitigating oxidative stress in captive-reared populations.