Effects of Sub-Lethal Atrazine Concentrations on Embryogenesis, Larval Survival and Growth of African Catfish, Clarias gariepinus (Burchell, 1822)

Abstract

The toxicity of environmentally relevant concentrations of atrazine on exposed fertilized eggs of Clarias gariepinus was evaluated in a 96hour static non-renewal bioassay. After exposure to atrazine concentrations of 0 (control), 4, 8, 12, and 16 μgL1 in water, first mitotic cleavage in the control occurred at 40 minutes after fertilization. The first cleavage did not occur in the 8 μgL-1 treatment group until 60 minutes after fertilization. Similar dose depended delayed cleavage was observed across atrazine exposed eggs. The first larvae emerged 22 hours from the time of fertilization at 27.00C in both control and atrazine treatment groups. However, hatching rates significantly differed between the control and atrazine exposed eggs (P<0.05) with 73.3% hatching rate in the control and 3.3% among the exposed eggs treated with 16μgL-1 of atrazine. Among the morphological deformities observed in the larvae of atrazine exposed eggs, kyphosis occurred more frequently with 60% of emerged larvae in the 16 μgL-1 atrazine treated group exhibiting the deformity. Morphometry showed significantly reduced head length, body length, body weight, and yolk diameter in 16 μgL-1 atrazine exposed eggs compared to the control. These results indicate that atrazine disrupted embryonic process and delayed hatching with severe larvae deformities.