METABOLIC AND OSMOREGULATORY RESPONSES OF THE SEA BASS LATES-CALCARIFER TO NITRITE EXPOSURE

Sea bass (Lates calcarifer) were exposed to seawater containing 0, 30, 50, or 80 mg L-1 NO2-N for 4 days, and changes in metabolite levels a nd enzyme activities were assessed. Distinct signs of osmoregulatory d ysfunction were evident in nitrite-exposed fish as serum Na+ and Cl- l evels were elevated and branchial Na+-K+-ATPase activity was significa ntly reduced. Serum lactate and protein levels were significantly elev ated and lowered respectively only at the highest nitrite level (80 mg L-1 NO2-N). Significantly increased serum ammonia and urea and decrea sed serum glucose and liver glycogen levels were evident also at lower nitrite levels. Liver water, liver protein and lactate, brain and mus cle lactate, and muscle water content were unaffected. In the liver, s ignificant decreases were observed for the activities of glycogen phos phorylase a, glutamate-oxaloacetate transaminase, and glutamate dehydr ogenase, but the activities of lactate dehydrogenase, isocitrate dehyd rogenase, glucose-6-phosphatase, glutamate-pyruvate transaminase, and glucose-6-phosphate dehydrogenase were unaffected. While ATP, ADP, and AMP levels were all lowered in nitrite-exposed fish, the adenylate en ergy charge was maintained at fairly constant level. By producing ammo nia via the degradation of AMP to IMP, stabilization of the adenylate energy charge can be achieved. It is postulated that this event probab ly represents an adaptive strategy employed by the sea bass to counter act nitrite toxicity. (C) 1997 by John Wiley & Sons, Inc.