Acute toxicity and ethological responses in African catfish Clarias gariepinus juveniles to the herbicide, Ronstar®

Abstract

The toxicity of the herbicide Ronstar® to Clarias gariepinus and the behavioural responses of individual fish were studied in a static renewal bioassay system. One hundred and eighty juveniles of C. gariepinus (mean weight 58.86 ± 2.46 g and mean length 24. 6 ± 1.02 cm) were exposed to different concentrations (0.0. 1.0, 3.0, 6.0, 9.0 and 12.0 mg l^–1) of Ronstar for 96 h. The mortality and behavioural responses to the test concentrations were recorded every 24 h. The LC₅₀ of Ronstar at 24, 48, 72 and 96 h were 48.67 ± 4.82, 9.62 ± 1.07, 7.86 ± 0.062 and 1.72 ± 0.041 mg l⁻¹, respectively. The mortality of C. gariepinus increased with both duration of exposure to, and concentration of, herbicide. Compared with the control, the aberrant behavioural responses observed include uncoordinated swimming, lethargy, increased opercula and tail beats, as well as the frequency of coming to the surface to gulp air. The opercula and tail beats, as well as the frequency of coming to the surface, were significantly higher (p < 0.05) than the control within the first 48 h of exposure. The current study underscores the importance of integrating ethological changes in fish as an early warning signal of pollution into ecotoxicological surveillance programme of water bodies.

Keywords: barbel, behaviour, bioassay, lethality, mortality, survival