ABSTRACT

The herbicide atrazine is widely used in agriculture for the production of corn and other crops. Because of its physical and chemical properties, atrazine is found in small concentrations in surface waters—habitats for some species. The present study was undertaken to evaluate the sub-lethal toxicity and effects of the herbicide atrazine on the behavioural responses and growth performance of Clarias gariepinus fry. The experiment had four treatments and a control group. The sub-lethal concentrations of atrazine used were; 0.03, 0.3, 3 and 30µg/l. Exposure of fry to the various treatments lasted for 48hours before withdrawal from exposure media and then monitored till the 28^th day. Growth indices measured include length, weight, growth rate, specific growth rate and condition factor. Growth rate was observed to reduce with increasing concentration of atrazine. However, the growth pattern across the treatment groups was observed to be negatively allometric irrespective of treatment concentrations. Fry in all treatment tanks exhibited abnormal behaviours characterised by erratic/agitated swimming, loss of equilibrium, frequent surfacing and hanging on water surface and discolouration. Mortality rate was highest in the 30µg/l group while least mortality was recorded in the 0.03µg/l treatment.This present study revealed that atrazine poses threat to Clarias gariepinus and other non target aquatic fauna even at low concentrations. Therefore, the use of atrazine especially in close proximity to water bodies should be monitored.