Pathological and toxicological studies on malathion to determine the optimum dose level used to eradicate Lethocerus niloticum insect preadating fish [electronic resource].

Includes references.

Malathion is an organophosphate insecticide and acaricide that has been widely used in agriculture practice. Male Oreochromis niloticus fish were exposed to different dose levels of malathion for estimation of LC₅₀. The water bugs (Lethocerus niloticum) were exposed to the same dose levels for recording the mortality percentage. From the obtained mortality data in both fish and bugs ,the average dose level of malathion that causing death in water bugs without any lethality in fish. Was estimated Another group of Oreochromis niloticus. fish and water bugs (laboratory introduced to the glass aquaria) were exposed to the average dose level of malathion for 24 & 96-hours. The toxic and pathological effects of such dose level on fish were investigated. Gonadosomatic index, some serum hormones (testosterone, T₃ and T₄) and enzymatic activities in brain tissue (AChE, LDH) were also investigated . The obtained LC₅₀ of malathion was 0.70 mg/L while the average dose level causing mortality in water bugs without any lethal effect on fish was 0.26 mg/L. The results revealed significant decrease in. gonadosomatic index in the group of fish exposed to the average dose level of malathion for 96-hours. There were marked significant reduction in the serum hormones after the same period of the exposure and inhibition of the enzymatic activities of brain tissue of intoxicated fish, which was obvious at 96-hours for both enzymes (AchE- LDH). histopathological findings, which revealed the presence of vacuolar degenerative changes of the hepatocytes and severe congestion of the hepatoportal vessels. The histopathological changes in spleen include lymphocytic depletion, melanomacrophage center devoid of melanin and activation of haemopoietic elements. Gills showed congestion of the lamellar capillary, oedema and eosinophillic granular cell infiltration. The hyperplasia and fusion of secondary lamellae were also noticed. The histopathological alterations in testis revealed degeneration of germinal epithelium and absence of spermatozoa in the seminiferous tubule lumenae. Brain of intoxicated fish showed focal gliosis and oedema while thyroid gland showed absence of colloid in the lumenae of some follicles. Statistical analysis of the obtained data denotes that the average dose level of malathion is effective for eradication of water bugs without any adverse effect on fish when applied only for 24-hours.

Summary in Arabic.

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