Nitrite intoxication of common carp (Cyprinus carpio L.) at different water temperatures

Abstract

Common carp (Cyprinus carpio L.) were exposed to nitrite (1.45 mmol·l-1 NO2-) for 48 hours at 14°C and 20°C, in order to investigate the mechanism of nitrite poisoning at these water temperatures. The effect of nitrite exposure on fish was assessed on selected haematological and biochemical indicators of the blood. Moreover, nitrite accumulation in the blood, liver and muscle was measured. Nitrite exposure produced high levels of methaemoglobin (88.2 ± 3.3% and 92.9 ± 6.1%) at both water temperatures compared with controls (0.3 ± 0.6% and 2.6 ± 3.0%). High fish mortality occurred in experimental groups (30% and 51%) compared with controls (0%). Nitrite exposure also resulted in an accumulation of nitrite in the fish body. The highest nitrite levels developed in the blood plasma, followed by the liver and muscle, respectively. Carp concentrated nitrite in the blood plasma and tissues to markedly higher levels at higher temperature (20°C). The plasma nitrite concentrations (10.5 ± 1.9 mmol·l-1) were in this case more than 7 times higher than the environmental one. At lower temperature (14°C), plasma nitrite concentration reached 5.0 ± 1.5 mmol·l-1. In either event, plasma K+ levels increased and Cl- levels and osmolality remained unchanged. Plasma Na+ levels slightly decreased at the higher temperature. Nitrite-exposed fish showed lower haematocrit values (PCV) at both experimental temperatures compared with controls. At 20°C, the blood haematocrit decrease (0.20 ± 0.02 l·l-1) was accompanied by a low erythrocyte count (1.05 ± 0.12·1012 l-1) and by a low haemoglobin level (51 ± 11 g·l-1). At the lower temperature (14°C), the haematocrit decrease (0.25 ± 0.02 l·l -1) was caused by a low mean corpuscular volume (167 ± 27 fl). No significant changes were observed in the mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), or selected erythrocyte dimensions (major axis, minor axis and aspect ratio).