Toxicity of roundup (a glyphosate product) to fingerlings of Clarias gariepinus
Acute static renewal bioassays were conducted on fingerling and adult of Clarias gariepinus (mean weight, 1.22 ± 0.6g; mean total length, 5.25 ± 1.25 cm) using the herbicide, Roundup (glyphosate). In the acute study, fingerlings were exposed in triplicate to 0.0, 14.0, 16.0, 18.0, 20.0 22.0, and 24.0 mg/l of the herbicide for 96 hours to determine general behavioural responses and specific responses (opercular beat frequency (OBF), tail beat frequency (TBF), lethal concentration (LC50) and median lethal time (MLT50). Exposed fish showed initial stress responses such as increased opercular ventilatory rate, dash and erratic swimming and gasping for air. The pattern of response of TBF to time and concentration of the herbicide was irregular, whereas that of OBF tended to decrease with increase in time, but increased with increase in concentration. Cumulative mortality values increased with exposure time. The effect of exposure time on the behavioural variables was: TBF (p > 0.05), OBF (p < 0.001) and cumulative mortality (p < 0.01) and that for concentrations were TBF (p > 0.05), OBF (p < 0.01) and cumulative mortality (p< 0.001). Interactions between time and concentration produced significant effect only in cumulative mortality (p < 0.01). The 96 hour LC50 of Roundup on the fish was 19.58 mg/l. The MLT50 decreased with exposure concentration with 24 mg/l killing half the exposed fish at 19.69 (17.41 - 21.94 CL) hours. Results from this study show that the herbicide cannot be described as having “low toxicity and being environmentally friendly” as suggested by the manufacturer, Monsanto.