Efficacy of Malathion on Mortality of A Fresh Water Air-Breathing Cat Fish, Hetempneustes Fossilis (Bloch) During Different Developmental Stages

摘要

Malathion is one of organo-phosphorous compounds, used against infestation of pests such as Hieroglyphic banian, Pachydiplosis oryzae, aphids, hoppers, psyllids, bugs, caterpillars, flea, beetles and mites etc in crop fields. Different doses of Malahion 50% EC was given to afresh water, air-breathing cat-fish, Heteropneustesfossilis (Bloch ) during different developmental stages. The pesticide directly affects the metabolic activity and increases fish mortality. The mortality offish gradually declineafter 20 days of hatching (1.1 to 1.2cm body length and 70-72 mg body weight) when airbreathinghabitcomeintoexistence After thedevelopmentofair-breathing organs the fry start acquiring resistance against the toxic effect ofthe pesticide as they rely more on atmospheric air. LC_(50) and LC_(100) value ofthe pesticide on juveniles for 24, 48, 72 and 96 hours and 10° C and pH 7,6 were recorded 19.0, 18.0, 17.5, 17.0 ppm and 35.4 34.0, 33.5, 33.0-ppm respectively LC_0 value of Malathion forjuvenile and adult fish was found to be 12,0 and 16,0 ppm Irrespectively in the present study. The fry and fingerlings results insignificantly and died even on very low concentration (8 ppm, 96 h). The suitable age of the fish which is least susceptible to the noxioustoxic effect of malathion recorded was 8-9 months. At this stage an optimum doseof malathion was ascertained 500 to600 m! in 12-15 litre of water/ha in water column of 0.4 to 0.5 meter which is helpful in fish cultureas well as control of pests in low lying areas.