Embryotoxicity of chlorpyrifos on gastrulation, segmentation, and hatching of <i>Clarias gariepinus</i> (Burchell, 1822)

Abstract

This study aimed to investigate the effect of chlorpyrifos on the embryonic development of Clarias gariepinus. Freshly fertilized eggs of C. gariepinus were subjected to varying concentrations of chlorpyrifos (0.01, 0.1, 1.0, and 10 μg L^-1) during embryogenesis in a static renewal bioassay. The investigation focused on three crucial stages of embryogenesis: gastrulation, segmentation, and hatching. During the gastrulation stage, observations of germ rings, caudal edge, and cephalic edge were consistent across both treatment and control groups. Results from the segmentation stage revealed complete somite blocks in both treatment and control groups. At hatching, the optic primordial, myotomal muscle, yolk sac, notochord, and mouth gape were fully formed at 24 hours posthatching in the control and treatment groups, except at the highest concentration (10 μg L^-1), where hatching did not occur. Notably, there were no significant aberrations during the embryogenesis period across the treatments. The hatchability test indicated that at the lowest concentration of chlorpyrifos (0.01 μg L^-1), 60% of the thirty fertilized eggs hatched. The 0.1 μg L^-1 treatment exhibited a hatching rate of 40%, while the 1.0 μg L-¹ treatment group showed a hatching rate of 20%. Although exposure of catfish embryos to chlorpyrifos at reduced concentrations did not result in significant effects, except at 10 μg L-1, the mere presence of chlorpyrifos in water bodies underscores the need for further evaluation of the subtle effects at environmentally relevant concentrations, which can only be identified through mechanistic analysis, on the development of fish eggs, larvae, and other aquatic fauna.