Toxicity of Cassava (Manihot esculenta Crantz) effluent on the Nile tilapia, Oreochromis niloticus (L) under laboratory Conditions

Abstract

Analysis of cassava tuber was conducted to determine some of the active ingredients and the toxicity of cassava effluent on the fingerlings of the Nile Tilapia, Oreochromis niloticus (L). The phytochemical analysis indicated the presence of hydrogen cyanide, oxalate and phytate. While hydrogen cyanide and oxalate concentrations were high in the fermented effluent than the fresh cassava sample, the reverse was the case with phytate. Both the acute and sublethal concentrations of the cassava effluent resulted in a number of physiological dysfunction of the test fish. The 96 hour LC50 was 0.91 mg l-1. The toxicant led to initial increase in the opercular ventilation rate, which then decreased below the status quo by the end of the 96 hours. Restlessness, immobilization, loss of balance and air gulping were commonly observed before death during the acute bioassay. Histopathological examination of the kidney, gill and liver of the treated fish indicated damages, ranging from oedema and telangiectasis of the gill lamella and gill hyperplasia to vacuolation of the liver cells and necrosis. These results are discussed in the light of effluent discharge in aquatic ecosystems and the management implications on biodiversity.


Key words: Cassava effluent, toxicity, tilapia, aquatic ecosystem


Journal of Aquatic Sciences Vol.17(2) 2002: 89-94