Hematological and enzymatic responses of Nile tilapia Oreochromis niloticus during short and long term sublethal exposure to zinc
A.1, Younis, E. M.1*, Abdel-Warith, A. A.1,2 and Al-Asgah, N. . 2012
Freshwater fish Oreochromis niloticus were exposed to sublethal concentrations of zinc for short and
long terms. Responses of hematological parameters which include red blood cells count (RBC) and
hemoglobin content (Hb) were investigated. Serum aspartate aminotransferase (AST) and alanine
aminotransferase (ALT) activities were also determined. Two hundred and forty fish (24.30 ± 2.85 g)
were distributed randomly in twenty four glass aquaria (80 L) with stocking density of 10 fish for each.
The aquaria were divided into two groups: the first group was exposed for one week to 2, 4 and 6 mg/L
of ZnCl2 which represent 0.25, 0.50 and 0.75 of Zn LC50, respectively with three replicates for each
concentration, in addition to 0.00 LC50 as the control; while the second group was exposed to the same
concentrations of ZnCl2 with the same replicates for 4 weeks. The results of hematological parameters
indicated that RBC and HB were significantly increased with increasing the concentration of ZnCl2
sequentially for both short and long exposure periods. The enzymatic estimation showed that the
activity of AST and ALT also significantly increased sequentially in zinc treated fish at both exposure
periods. Results of the present study suggest that sublethal concentrations of zinc affect the
hematological changes and impaired liver functions. These parameters can be useful in environmental
biomonitoring of zinc contamination.
