L-carnitine protects fish against acute ammonia toxicity.

1. Juvenile chinook salmon (Oncorhynchus tshawytscha) were injected intraperitoneally (i.p.) with 0.25 M mannitol followed 1 hr later by an i.p. challenge of ammonium acetate. 2. At 10.75 mmol ammonium acetate/kg body weight, 98% of the fish showed signs of ammonium toxicity and 69% died. 3. Substitution of L-carnitine (10-16 mmol/kg) for mannitol afforded striking protection from the subsequent challenge with ammonium acetate; 67% showed no signs of ammonia toxicity and only 4% died. 4. Of other quaternary amines tested, trimethylamine oxide also afforded protection, but betaine and choline did not.