Potential Use of the Freshwater Teleost, Labeo rohita (Hamilton, 1882) as a Bio-indicator of Zinc Toxicity

Abstract

Fish occupying the topmost niche in aquatic food chain has always been proved to be successful bio-indicators. The present study is focused on the effective use of L. rohita, an economically significant carp as a bio-indicator of zinc pollution through its several physiological, histopathological biomarkers. Primarily, acute toxicity test is performed in which the carp fingerlings are exposed to different concentrations (10, 20, 40, 80, 160, 320 ppm) of zinc sulphate. 96 hour LC50 value is determined to be 100 ppm. It is taken as lethal concentration and the fishes are exposed to it for a period of 96 hours during which wide range of behavioural abnormalities are evidenced like general hyperactivity, surfacing activity, hyper-opercular activity, and erratic swimming pattern. It is followed by loss of balance and convolutions. One fifth of the lethal concentration is taken (i.e., 10 ppm) as sub-lethal concentration and fishes are exposed to it for a period of 15 days during which growth, behaviour, oxygen consumption, histopathology, hematology and genotoxicity are studied. Negative growth performance is observed with insignificant length increment up to 0.24 % and significant weight reduction up to -2.38 %. Wide range of behavioural abnormalities are evidenced which includes, erratic swimming, hyperactivity, surfacing activity and depression in appetite. Besides, general body discolouration and haemorrhage are observed as well. Rate of oxygen consumption showed a time dependant decrease which ranged up to -49.10%. Gills of the fishes are shown to have conspicuous histopathological alterations like lamellar necrosis, lamellar fusion, lamellar erosion, epithelial lifting and epithelial swelling. Key-words- Bioindicator, L. rohita, Zinc sulphate, Growth, Behaviour, Oxygen Consumption, Histopathology