Hematological and enzymatic responses of Nile tilapia Oreochromis niloticus during short and long term sublethal exposure to zinc

Abstract

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 LC₅₀as 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.

Key words: Nile tilapia, Oreochromis niloticus, liver enzymes,  hematological parameters, LCa₅₀ of zinc.