Abiotic and biotic factors affecting the immune system of aquatic species: A review

• Abiotic environmental factors, including temperature, salinity, pH, hypoxia, and pollutants, significantly influence immune functions in aquatic animals. • Pathogenic and parasitic infections, as biotic stressors, markedly inhibit both innate and adaptive immune responses, thereby heightening susceptibility to disease. • Aquatic species' immune systems demonstrate structural and functional diversity, influenced by evolutionary adaptations to specific ecological niches. • Integrating environmental and immunological knowledge is essential for enhancing aquaculture resilience, disease management, and the sustainability of aquatic ecosystem health. The immune response of aquatic organisms is affected by biotic and abiotic elements, determining their health and survival. Thus, this review aimed to integrate existing research on how environmental factors (temperature, salinity, pH, pollution) and biotic factors (infections, parasites, and the microbiome) shape immune function in aquatic animals. Aquatic animals, which include fish, crustaceans, and molluscs, have innate and adaptive immune systems that are predominant in non-mammalian species. Abiotic stresses such as temperature variations and pollution can compromise immune responses, putting them at higher risk of infection. Biotic interactions also influence immunological responses, resulting in immunosuppression under elevated pathogen burden and interspecies competition. Therefore, understanding these aspects in aquaculture, ecosystem management, and conservation initiatives can offer insights into the impact of environmental changes and stresses on the immunological resilience of aquatic animals.