Changes in Differential Leucocyte Count (DLC) were evaluated in the blood of the fish species Clarias batrachus and this was used as an in situ indicator of the species’ exposure to zinc.Due to feeding and living in the aquatic environments, fish
are particularly vulnerable and are heavily exposed to pollution because they cannot escape from the detrimental effects of pollutants. In the present study, the effects of zinc on the DLC(small and large lymphocytes, neutrophils, monocytes, eosinphils
and basophils) were examined under three different concentrations of zinc (1.00 ppm, 3.00 ppm and 6.00 ppm) during 7, 14, 21 and 28 days exposure period. During examination, the percentage of both lymphocytes were significantly lower as exposure time and concentration increased while in the case of neurtophils and monocytes, counts, were higher. Eosinophils showed slight increase whereas basophils showed fluctuations in their results. The study of this research infers that the essential metal in undesirable condition can affect the fish health. DLC represents a suitable biomarker of environmental
health and provides a tool for biomonitoring water quality.