Author(s): Temitope Jegede

Abstract: A static bioassay was conducted to determine the 96h median lethal level (LC₅₀) of malachite green on Tilapia zillii fingerlings (6.35 ± 0.4 g and 6.23 ± 0.8 cm respectively) and to establish histological changes in the gill, liver and heart. LC₅₀ of T. zillii fingerlings was determined graphically as 1.65g MG /L of water. Fish displayed the following behaviours gasping for oxygen, erratic swimming, loss reflex, discolouration, irregular operculum and tail beat frequencies during 96 h exposure. Histological examination revealed alteration in the gill architecture vis congestion, degeneration and erosion of gill filaments, gill ray and lamellae. The liver showed vacuolation of the liver cell, hydropic degeneration of the hepatocellular parenchyma, chronic inflammation of hepatocyte and cellular infiltration of the periportal region. Lastly the heart showed evidence of mild lesion, slight disintegration in the heart cell arrangement, degeneration of the adipose tissue surrounding the sinus venosus, severe coagulative necrosis of the atrioventricular and ventriculobular valves at high concentrations of malachite green.

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