Acute toxicity of gramoxone to Oreochromis niloticus (Trewavas) in Nigeria

The acute toxicity of paraquat (1,1-dimethyl-4,4-bipyridinium dichloride) to fingerlings of Oreochromis niloticus (Trewavas) was determined in 96 hr static bioassays. During the assays opercular ventilation and tail fin movement rates of the fish were determined. Haemotological parameters of the blood and histopathology of the gills were observed. The 96 hr LC50 of paraquat to fingerlings of O. niloticus was observed to be 11.84 mg L-1. Histopathology of gills of the fish exposed to 12.00 mg L--1,L- and 14.20 mg L-1 showed a dose-dependent disruption of the architecture of the lamellae, filament hyperplasia and atrophy, leading to impairment in oxygen uptake. Other symptoms of toxicosis in exposed fish include loss of equilibrium; agitated swimming; air gulping; haemorrhaging of the gills, pectoral and pelvic fins; period of quiescence and finally, death.