EFFICACY OF MALATHION ON MORTALITY OF A FRESH WATER AIR-BREATHING CAT FISH, HETEROPNEUSTES FOSSILIS (BLOCH DURING DIFFERENT DEVELOPMENTAL STAGESPankaj Kumar, B. Sharma & A.P.Mishra
Malathion is one of organo-phosphorous compounds. used against infestation of pests such as Hieroglyphus 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 a fresh water, air-breathing cat-fish, Heteropneustes fossil is (Bloch.) during different developmental stages. The pesticide directly affects the metabolic activity and increases fish mortality. The mortality of fish gradually decline after 20 days of hatching (I. Ito 1.2 cm body length and 70-72 mg body weight) when air breathing habit come into existence. After the development of air-breathing organs the fry start acquiring resistance against the toxic effect ofthe pesticide as they rely more on atmospheric air_ LCsoand Lc. value of the pesticide on juveniles for 24, 48, 72. and 96 hours and 10° C and pH 7.6 were recorded I 9.0, I 8.0, 17.5, 17.0 ppm and 35.434,0, 33.5, 33.0 ppm respectively LC, value of Malathion forjuvenile and adult fish was found to be 12.0 and I 6.0 ppm h) respectively in the present studyThe 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 noxious toxic effect of malathion recorded was 8-9 months At this stage an optimum dose of malathion was ascertained 500 to600 ml in 12- 1 5 litre of water/ha in water column of 0.4 to 0.5 meter which is helpful in fish culture as well as control of pests in low lying areas.
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