ABSTRACT

Glyphosate herbicide is used to kill weeds. It is known to be a contaminant of fresh water and marine ecosystem. Therefore, a study was designed to determine the acute toxicity effects of glyphosate herbicide on a fresh water fish, Clarias gariepinus fingerlings. Clarias gariepinus were exposed to a concentration of glyphosate herbicide at 25ppm, 50ppm, 75ppm and 1 00ppm in a static bioassay for 96hrs ( 4days). The LCso of glyphosate herbicide was estimated at log toxicant concentration as 1.40, l.70, l.90 and 2.00 µg/1 at 84h, 64h, 56h, 34h respectively. This shows that the impacts are dose and time dependent with respect to incease in mortality rate. Values of the lower and upper limits of toxicities were 22.95ppm and 25.76ppm respectively. The threshold value (soft level) was 22.51ppm. Statistical analysis of the data showed a significant difference between the 96-hrs LCso values for the experimental fish at P<0.05. During the exposure period the fish showed such signs as frequent surfacing with irregular opercular movement, erratic swimming, surfacing erosion of slime layer, skin lesion, nesting at the tank bottom, fast jerky movement, and no response to gentle prodding before death. The result suggest that, although glyphosate is a useful herbicide in agricultural and forestry because of its residual effect on non- target organism, it should be applied carefully using lowest possible doses or concentration to avoid unforeseen toxicological effects.