Adaptive Mechanisms of Fish under Conditions of Ammonia Toxicity

Ammonia is the main excretory substance resulting from the catabolism of proteins and amino acids in most aquatic animals, especially in teleost fishes, that is excreted through the gills. Ammonia toxicity is one of the most common types of poisoning in fish. Fish have been exposed to this type of toxicity since ancient times and have tried to adapt to it, an adaptation that has developed over the years and has become part of their evolutionary process. This adaptation is already happening and will continue in the future. The degree of adaptation varies according to the living conditions of different fish. Species that were more exposed to high concentrations of environmental ammonia became more adaptable. The mechanism of this adaptation is different in different organs. The liver and gills, which play a greater role in the metabolism, detoxification, and excretion of ammonia, have achieved higher levels of adaptation. Studies related to ammonia compatibility are less common in other organs, such as the skin. Increasing environmental ammonia also affects the social relationships and individual behaviors (for example, swimming patterns) of fish, and social adaptation must also be considered. This study tries to review the cellular-molecular mechanisms of adaptation to increasing environmental ammonia separately in organs.