Pyrethroids like Lambda Cyhalothrins, are synthetic insecticides that contaminate and modify the physico-chemical integrity of receiving water bodies and are toxic to the resident life forms. When applied at a given site may find their way into natural water bodies through leaching, precipitation, percolation, drift, or runoff. The aim of this study was to determine the acute toxicity, behavioural effects and histopathological effects on gills of Sarotherodon melanotheron exposed to Lambda Cyhalothrin (LCT) in brackish water. Four hundred and sixty (460) fingerlings of Sarotherodon melanotheron (mean length - 8.0 cm) and (mean body weight - 8.9 g) were exposed to various concentrations (3, 5, 7, 9, 11 and 13 mg/L) of a pyrethroid insecticide - Lambda Cyhalothrin in brackish water in the Marine Pollution Monitoring Laboratory in the University of Port Harcourt, Nigeria. An acute toxicity bioassay (96 h) was carried out to determine the LC50 of the toxicant. The histopathological effects of the toxicant on the gills and behaviour of fish were recorded. Physicochemical parameters of the test solution were measured. At the end of the test period, fish from each concentration was dissected and the gills removed for histological studies following standard methods. The results revealed a 96 h LC50 of 9 mg/L. The behavioural-somatic responses include: erratic swimming, surfacing, hyperventilation, loss of reflex, skin (scale) discolourations, caudal bending, etc. These aberrations were seen to have increased with corresponding increase in the concentrations of the toxicant and length of exposure. There were pathological alterations such as cellular infiltrations, fusion of the lamellar, hyperplasia, tissue inflammations, vacuolation, tissue degeneration and necrosis that appeared more severe with increasing concentrations. The observed behavioural and histopathological alterations at the various test concentrations were indications that the toxicant may have impaired their normal physiological integrity. The findings also showed that LCT although toxic to Sarotherodon melanotheron in brackish water, required high concentrations. The use of LCT in brackish water, fish farms or zones close to aquatic water systems should be discouraged. (C) 2019 The Author(s). Published by Elsevier B.V. on behalf of African Institute of Mathematical Sciences / Next Einstein Initiative.
