Ammonia toxicity and adaptive response in marine fishes – A review

High environmental ammonia has become a universal problem for aquatic animals, especially in fish and induces a range of ecotoxicological effects. Perhaps waterborne ammonia is one of the most notorious pollutants in aquatic habitats. The effects of rising ammonia levels do not act in isolation; increasing human pressure including climate change (e.g. temperature, rising CO2, hypoxia etc.) creates a variety of additional deleterious impacts on animals. The salinity gradient of some marine ecosystems has gradually reduced over the last few decades, which alters a suite of physiological and behavioural performance of marine fish with a severe threat on osmo-regulation. It has been documented that environmental salinity influences the ammonia toxicity in several marine species. Such interactive effect between ammonia toxicity and salinity challenge on differential physiological and metabolic compensatory responses has not been fully revealed in fish. It is essential to pay attention to the levels of salinity and ammonia in environment, and how the two interact, particularly when dealing with estuarine aquaculture.