The toxic implications of fresh water contamination with zinc in the catfish,
Clarias albopunctatus
(Lamonte and Nicole, 1927), and the effect of a co-contamination with a sub-lethal dose of glyphosate (Roundup) was studied using the static bioassay model. Thirty six fish were divided into 3 equal groups. Fish in Group 1 were placed in normal tap water, and served as the control group, while fish in Groups 2 and 3 were placed in water contaminated with ZnSO
4 and ZnSO
4 + glyphosate, respectively. The study lasted for 96 hours (though sampling was done at the 48
th hour). Biochemical markers of toxicity were measured and the fish liver and gill histology were studied using standard protocols. The results show that ZnSO
4 was significantly toxic to the fish only after 96 hours. Co-contamination of the water with both toxicants was found to ameliorate the toxic effects of ZnSO
4 significantly. The metal chelating property of glyphosate may be responsible for the observed attenuation of toxicity in the fish in Group 3.
