Effects of nitrite exposure on haematological parameters and growth in clown knifefish (Chitala ornata, Gray 1831)

Abstract

Physiological responses and growth of clown knifefish (Chitala ornata) (initial weight of 11-12 g) exposed to nitrite were investigated with three separate experiments. The first experiment was to determine the nitrite concentration causing 50% mortality in 96 hours (96-h LC50). The second experiment examined the effects of different nitrite concentrations on haematological parameters. The third experiment investigated into the effects of different nitrite concentrations on fish growth including 4 treatments such as control, 0.2 mM nitrite, 0.4 mM nitrite, and 4 mM nitrite for measuring growth parameters at days 0, 30, 60, and 90 days (sampling 30 fish/tank). The results showed that the clown knifefish had high nitrite tolerance with 96-h LC50 of 7.82 mM. There were significant increases in methaemoglobin and leukocytes while other haematological parameters decreased during nitrite exposures at the treatment of 4 mM nitrite. Particularly, methaemoglobin and the number of leukocytes increased from 0.4 to 29.5%, and from 39.89x103 to 72.33x103 cells/mm3, respectively. Differently, there were significant declines in the number of erythrocyte (3.19x106–2.33x106 cells/mm3), haemoglobin (10.47-7.04 mM), and haematocrit (38.07-26.5%) at the highest nitrite treatment. After 90 days, daily weight gain (0.25±0.02 g/day), specific growth rate (1.18±0.07 %/day), survival rate (59%) at the treatment of 4 mM nitrite were significantly lower than those of the control, but no significant difference was observed in such parameters between the control and the treatments of 0.2 or 0.4 mM nitrite.