Abstract
Laboratory study was undertaken to evaluate some haematological changes resulting from the exposure of a freshwater fish, Heteroclarias sp. to sublethal concentrations (5.0 and 10.0 mg L-1) of zinc in water for a period of fifteen (15) days. Three groups of ten fish were subjected to serial dilutions of the stock solution of zinc of 0 (control), 5.0 and 10.0 mg L-1 in three large plastic bowls of 60 litres capacity by the semistatic (renewal) method. At the end of the 15 days exposure period, blood samples were taken from the control and experimental fish. Blood was assayed for selected haematological parameters (haematocrit, haemoglobin, red blood cell counts, white blood cell counts, differential white blood cell counts, erythrocyte sedimentation rate, total plasma protein and plasma glucose concentration). The derived haematological indices of mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC) were calculated. Sublethal concentrations (5.0 and 10.0 mg L-1) of zinc caused a dose dependent decrease in haemoglobin values, coupled with a decrease in haematocrit values and red blood cell counts are obvious indication of anemia of the norm chronic type. The total white blood cell counts and the differential white blood cell counts were decreased except for the lymphocytes in which there was a slight increase. Plasma level of protein and glucose were also lower in the exposed fish when compared to the control. The haematological indices MCHC, MCH and MCV were also lowered. In conclusion, the changes observed indicate that haematological parameters can be used as an indicator of zinc related stress in fish on exposed to elevated zinc levels. Key words: Zinc, haematology, anaemia, glucose, protein, Heteroclarias,Nigeria.
Highlights
Zinc, an essential element, is one of the most common heavy metal pollutants
We have previously reported the chronic sublethal haematological effects of copper in fresh water teleost, Clarias isheriensis and some alterations in haematological parameters in C. isheriensis exposed to sublethal concentrations of water borne lead (Kori-Siakpere (1991, 1995)
The main haematological alteration resulting from exposure of Heteroclarias sp. to various concentrations of zinc in the water for 15 days includes significant decrease in haematocrit and haemoglobin concentration, and nonsignificant decrease in red blood cell counts and erythrocyte sedimentation rates (Table 2)
Summary
An essential element, is one of the most common heavy metal pollutants. Annune et al (1994b) reported that zinc could cause sub-acute effects that change fish behaviours. Sublethal levels of zinc have been known to adversely affect hatchability, survival and haematological parameters of fish (Cardeihac et al, 1981). Such observed behaviours include lack of balance since most fins are motionless in the affected fish, agitated swimming, air gulping, periods of quiescence and death
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