The loach Misgurnus anguillicaudatus reduces amino acid catabolism and accumulates alanine and glutamine during aerial exposure

The loach Misgurnus anguillicaudatus inhabits rice fields in Southern China . It encounters drought during summer and ammonia loading during agricultur al fertilization. In the laboratory, aerial exposure led to decreases in it s ammonia and urea excretion. Ammonia accumulated to very high levels in th e muscle and liver. Urea synthesis through the ornithine-urea cycle was not involved in ammonia detoxification in M. anguillicaudatus. However, M. ang uillicaudatus was capable of partial amino acid catabolism leading to the a ccumulation of alanine in the first 24 h of aerial exposure. This was appar ently coupled to a possible decrease in protein/amino acid catabolism. Thes e are not detoxification mechanisms but mechanisms that avoid internal foul ing by ammonia. Misgurnus anguillicaudatus was also capable of detoxifying internally produced ammonia in part to glutamine, which appears to be an im portant adaptation after 24 h of aerial exposure. However, unlike the case of the marble goby (Oxyeleotris marmoratus), there was no alteration to the kinetic properties of the hepatic glutamine synthetase. During dry seasons , M. anguillicaudatus moves actively on land until it encounters soft mud i n which it can bury itself through several strong wriggling actions of the body. Hence, it is possible that M. anguillicaudatus uses partial amino aci d catabolism to fuel its short period of activities on land and switches to the formation of glutamine to detoxify internally produced ammonia when it remains relatively inactive in the mud.