Haematological and biochemical profiles of carp blood following nitrite exposure at different concentrations of chloride

Haematological parameters of 2-year-old carp (Cyprinus carpio L.) were assessed to study the protective effect of chloride on the health of fish exposed to elevated nitrite concentrations. Four groups of carp were exposed to different concentrations of nitrite and chloride for 96 h (group E1: 67 mg L-1 NO2-, 11 mg L-1 Cl-; group E2: 67 mg L-1 NO2-, 100 mg L-1 Cl-; group E3: 0 mg L-1 O-2(-), 100 mg L-1 Cl- and group C: 0 mg L-1 NO2-, 11 mg L-1 Cl-). The main haematological response of carp to an acute exposure to nitrite (group E1) was a significant decrease (P < 0.05) in haemoglobin concentrations (53.40 +/- 6.61 g L-1), haematocrit (0.21 +/- 0.02 LL-1), erythrocyte count (1.13 +/- 0.12 TL-1), leucocyte count (7.1 +/- 4.19 GL(-1)) and lymphocyte count (5.28 +/- 2.51 GL(-1)), and a significant increase in methaemoglobin concentration (90.50 +/- 4.38%, P < 0.01) and mean corpuscular haemoglobin concentration (0.27 +/- 0.2 LL-1, P < 0.05). At higher chloride concentrations (group E2), a lower nitrite toxicity was observed. In group E2 carp, methaemoglobin made up 38.32 +/- 13.30%. Erythrocytes in carp exposed to nitrite showed qualitative changes. Compared with the control group C, group E1 carp showed a significantly higher number (P < 0.05) of elongated erythrocytes, with the nucleus located at one cell pole (0.519 +/- 0.388 TL-1). All erythrocytes of group E1 carp had remarkably clear cytoplasms compared with the cytoplasm in the control group C. The biochemical values found were comparable with those found in controls. The main histological lesions were found in the gills of carp exposed to nitrite and consisted of hyperplasia and an elevated number of chloride cells.