ABSTRACT

This study was carried out to determine sub-lethal effects of Atrazine herbicide in juveniles of Clarias gariepinus and Hybrid (Heterobranchus longifilis X Clarias gariepinus). Fish species were exposed to acute concentrations of 5mg/l, 10mg/l, 15mg/l, and 20mg/L of Atrazine, as well as sub-lethal doses of 0.6mg/l, 1.3mg/l and 2.5mg/L of Atrazine. Both experiments had a control each, which served as a reference point. The LC₅₀ value of atrazine established from the study was 12.5mg/L for both species. A total number of one hundred and twenty (120) juveniles each of Clarias gariepinus and Hybrids of mean weight 7.60±0.10g and mean standard length 3.51±0.13cm, (regardless of sex) were exposed to sub-lethal atrazine concentration for 12 weeks. The effect of the sub-lethal exposure of both fish species to atrazine, was evaluated using standard methods that assessed fish behaviour, histology, haematological, biochemical, proximate composition and atrazine accumulation in the muscles. Atrazine induced hyperactivity and loss of equilibrium at acute levels of exposure. The physico-chemical parameters obtained before and after the experiment were within the tolerated limit.  Histopathological analysis of the fish organs examined revealed varying degrees of pathological alterations to the gill and liver of both fish species. The gill showed alterations like fusion and shortening of primary and secondary lamella. The liver showed histopathological changes such as congestion of central vein and degeneration of hepatocytes amongst other alterations. Assessment of haematology and biochemical parameters revealed significant differences between exposed groups and control. Atrazine also has a dose dependent effect on the growth parameters, with both highest and lowest growth rate recorded in the control and exposed group of Hybrids respectively. Proximate composition of exposed groups was significantly different from the control of both species. Atrazine accumulation in the muscle was found highest in Hybrid juveniles exposed to highest Atrazine concentration (2.5mg/l). Results of the sub-lethal toxicity test showed that Atrazine was toxic to the both species in a dose-dependent manner. The toxicity assessment parameters were more pronounced in the exposed groups of Hybrids than Clarias gariepinus juveniles though not statistically different. All parameters for toxicity assessment showed significant differences in the exposed groups when compared to the control. The study revealed that Atrazine was moderately toxic to C. gariepinus and Hybrid (Heterobranchus longifilis X Clarias gariepinus) juveniles and affected the behaviour, haematology, biochemistry, histology, as well as growth of the fish. Hence, the use of the herbicide should be used with caution especially near water bodies.