Exposure of Siberian sturgeon (Acipenser baeri) yearlings (172.0+/-18 g; mean+/-S.D.) to several NO(2)(-)-N concentrations (0, 25, 130, 180 and 275 mg/l) was studied for 72 h in static tests. At 72 h, the median-lethal concentration of NO(2)(-)-N was 130 mg/l in water with high
chloride content (130.5 mg/l).
Nitrite exposure produced high levels of methaemoglobin (MetHb) but did not seem to cause mortality, as surviving fish showed higher levels (82.7+/-5.6%) than torpid specimens (60.8+/-4.5%). Levels of MetHb were unrelated to environmental and plasmatic
nitrite concentrations, as both torpid and surviving fish exposed to the highest
nitrite levels (275 mg/l of NO(2)(-)-N) presented similar concentrations of MetHb to those exposed to 25 mg/l of NO(2)(-)-N, thus indicating the ability of Siberian sturgeon yearlings to regulate plasmatic
nitrite levels and maintain them lower than the environmental concentration of the toxicant.
Nitrite exposure caused changes in the plasmatic electrolyte balance, which is characterised by extracellular
hyperkalemia, high plasmatic
chloride levels and low plasmatic
sodium concentration. Differences between the
nitrite concentration in the liver of torpid (46.3+/-9.0 mg/l) and surviving specimens (19.1+/-13.1 mg/l) exposed to several concentrations of NO(2)(-)-N suggest a significant contribution of the liver in
nitrite detoxification pathways, and would thus explain a possible
nitrite tolerance of Siberian sturgeon yearlings.