Effect of nitrite exposure on hematological parameters and blood respiratory properties in the sea bass Lates calcarifer

Abstract

AbstractChanges in hematological parameters and blood respiratory properties of Lates calcarifer in response to nitrite exposure were studied. Exposure to 10 mg · L−1 NO2‐N for 8 days resulted in significant increases in blood nitrite and methemoglobin contents. Total hemoglobin was reduced resulting in an overall decline in functional hemoglobin. There was no significant change in hematocrit and red blood cell count.In another set of experiments, hematological parameters and venous blood oxygen tension of L. calcarifer after exposure to 15, 20, 30, 50, and 80 mg · L−1 NO2‐N for 4 days were determined. Blood nitrite and methemoglobin content increased proportionally to the increase in ambient nitrite concentration. The methemoglobin content (as percent of total hemoglobin) of fish immersed in a nitrite concentration equivalent to the 96 h LC50 (93 mg · L−1 NO2‐N) was estimated to be 83%. Venous blood oxygen tension tended to decrease as nitrite concentration increased.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 arterial 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 (P50 = 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 dissociation curve (P50 = 5.9 ± 1.6 mm Hg; n = 0.99). The increased blood oxygen affinity in nitrite‐treated fish probably facilitated oxygen loading from water to the blood stream at the respiratory surfaces so as to compensate for the decline in oxygen carrying capacity. © by John Wiley & Sons, Inc.