Biochemical and molecular mechanisms to survive high environmental ammonia and terrestrial exposure in the Asian stinging catfish, Heteropneutes fossilis

Project Number
RI 3/15 CSF

Project Duration
May 2016 - May 2019


The Asian stinging catfish, Heteropneustes fossilis, is a freshwater teleost found in the Indian subcontinent. It breathes in water using its gills and in air with its air sacs. It inhabits derelict water bodies and burrows inside the mud during drought and is thus confronted with ammonia toxicity. Although it has been proposed that this fish can tolerate high ambient ammonia by detoxifying ammonia to urea through the ornithine-urea cycle, there is a dearth of knowledge on its capability of actively excreting ammonia through its gills or volatilizing ammonia using its airsacs. Previous works by the PI have shown that air-breathers like the giant mudskipper, Periophthalmodon schlosseri, the climbing perch, Anabas testudineus, and the walking catfish, Clarias batrachus, are capable of actively excreting ammonia while the weatherloach, Misgurnus anguillicaudatus, is capable of volatilizing ammonia when exposed to terrestrial conditions or high environmental ammonia. A recent study by the PI demonstrated that when H. fossilis is placed in 8 mmol l-1 NH4Cl, it is able to excrete ammonia into the ambient water though it is faced with an inward gradient of ammonia. Thus, this fish may also have the ability to actively excrete ammonia like the giant mudskipper, climbing perch or the walking catfish. Urea synthesis is an energy intensive process and thus it may not be an advantage to a teleost to possess such a mechanism to detoxify ammonia. The only fish that makes a lot of urea when exposed to land or high environmental ammonia is the lungfish. However, the lungfish aestivates when confronted with drought. Thus having the ability to synthesize and store urea may also facilitate the lungfish in conservation and retention of water during aestivation. Contrary, H. fossilis does not aestivate. Synthesising urea may not be the main strategy for it to survive terrestrial or high environmental ammonia. With the preliminary study conducted recently, the PI is confident that H. fossilis is capable of actively excreting ammonia and possesses mechanisms that enable it to actively excrete ammonia. The discovery of the mechanisms involved in active ammonia excretion can aid in the possibility of constructing artificial membranes for ammonia removal which is needed in the food industry, aquaculture, and blood dialysis in patients with acute liver failure. Thus, the PI proposed to investigate the biochemical strategies and the molecular mechanisms that enable this stinging catfish to survive terrestrial and high environmental ammonia exposure.

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