THE EFFECT OF TWO PESTICIDES DICHLORVOS AND PARAQUAT ON HETEROBRANCHUS LONGIFILIS (Valenciennes)

Abstract

Ninety-six (96) - hour bioassays were carried out to determine the toxicity of two pesticides, Dichlorvos and Paraquat on juveniles of Heterobranchus longifilis. Various concentrations in (mg/1) of 1.20, 1.40, 1.60, 1.80, 2.00 and a control were tested for Dichlorvos; while 4.30, 6.40, 8.50, 10.60, 14.90, 17.00 and a control for Paraquat. 96 hrs LC₅₀ at 95% confidence limit in mg/l were 1.32 for Dichlorvos and 7.67 for Paraquat. Heterobranchus longififis was more susceptible to Dichlorvos. Manifestation and survival times of the fish for each toxicant were not size dependent, rather they were concentration dependent, decreasing with increasing concentrations. Fading of colour of fishes, mucous secretion from gills and mouth, as well as, the expansion and swelling of the ventral surfaces of the opercular region were observed. Skin peeling was noticed in specimens treated with Paraquat. Quick burst of erratic swimming and general loss of equilibrium, darting movement and overturning time increased with increase in concentrations. The data obtained suggest that both pesticides are environmentally unfriendly and should be used with utmost restraint, especially in the aquatic environment where they could be hazardous to both aquatic life and man.


KEY WORDS: Dichlorvos, Paraquat, Manifestation, Mortality, Heterobranchus longifilis


Global Jnl Pure & Applied Sciences Vol.10(1) 2004: 55-60