EFFECT OF NITRITE EXPOSURE ON HEMATOLOGICAL PARAMETERS AND BLOOD RESPIRATORY PROPERTIES IN THE SEA BASS LATES-CALCARIFER

Changes in hematological parameters and blood respiratory properties o f Lates calcarifer in response to nitrite exposure were studied. Expos ure to 10 mg . L(-1) NO2-N for 8 days resulted in significant increase s in blood nitrite and methemoglobin contents. Total hemoglobin was re duced resulting in an overall decline in functional hemoglobin. There was no significant change in hematocrit and red blood cell count. In a nother set of experiments, hematological parameters and venous blood o xygen tension of L. calcarifer after exposure to 15, 20, 30, 50, and 8 0 mg . L(-1) NO2-N for 4 days were determined. Blood nitrite and methe moglobin content increased proportionally to the increase in ambient n itrite concentration. The methemoglobin content (as percent of total h emoglobin) of fish immersed in a nitrite concentration equivalent to t he 96 h LC(50) (93 mg . L(-1) NO2-N) was estimated to be 83%. Venous b lood oxygen tension tended to decrease as nitrite concentration increa sed. In a third set of experiments, sea bass were exposed to 50 mg . L (-1) NO2-N for 4 days. Exposure to nitrite resulted in lowered arteria l and venous blood oxygen tensions, arterial and venous oxygen content , and blood oxygen capacity. However, no change in Venous blood pH was observed between control and nitrite-treated fish. The blood of Lates has a relatively low oxygen affinity (P-50 = 14.5 +/- 2.3 mm Hg) with a Hill coefficient (n) of 1.46. Exposure of fish to 50 mg . L(-1) NO2 -N resulted in a leftward and upward shift of the blood oxygen dissoci ation curve (P-50 = 5.9 +/- 1.6 mm Hg; n = 0.99). The increased blood oxygen affinity in nitrite-treated fish probably facilitated oxygen lo ading from water to the blood stream at the respiratory surfaces so as to compensate for the decline in oxygen carrying capacity. (C) 1995 b y John Wiley & Sons, Inc.