Toxic impacts of nitrite on fish and intervention strategies

Intensive and recirculating systems in aquaculture enhance nitrite generation due to microbial nitrification of ammonia derived from protein metabolism. Natural waters may also include nitrite under specific situations. In aquatic systems, fish are susceptible to the toxic impacts of nitrite exposure, which enters via chloride channels in the gill epithelium, disrupting ion regulation. As a well-known aquatic toxicant, nitrite affects aquatic animal growth, blood oxygen-carrying capacity, and physiological homeostasis, including oxidative damage, abnormal immune response, endoplasmic reticulum stress, and apoptosis. The toxic impact of nitrite on fish is modulated by multiple environmental and biological variables, including temperature, salinity, dissolved oxygen levels, ammonia, life stage, and duration of exposure. Therefore, a thorough understanding of these aspects is required for nitrite management. Diverse methods and management techniques have been developed to combat nitrite-associated stress. Adopting improved nutritional approaches, such as feeding antioxidants with the dietary protein in conjunction with efficient biological filters, has been proven to lessen the negative effects of nitrite. This review recapitulates various toxic effects of nitrite on fish, factors that affect its toxicity, and proposes management strategies to reduce nitrite toxicity. It will act as a ready reference for different stakeholders, such as farmers and researchers for the sustainable development of aquaculture.