The release of pollutants, especially heavy metals, into the aquatic environment is known to have detrimental effects on such an environment and on living organisms including humans when those pollutants are allowed to enter the food chain. The aim of this study is to analyse the damage to Clarias gariepinus' liver caused by exposure to different concentrations of copper. In the present study, samples of C. gariepinus were exposed to sub-lethal copper sulphate (CuSO) concentrations (from 0.2 to 20.0 mg/L) for 96 h. Physiological and behavioural alterations were observed with respect to their swimming pattern, mucus secretion and skin colour. Mortality was also observed at high concentrations of copper. Histopathological alterations of the liver were analysed under light, transmission and scanning electron microscopies. The liver of the untreated group showed normal tissue structures, while histopathological abnormalities were observed in the treated fish under light and electron microscopes with increased copper concentrations. Histopathological abnormalities include necrosis, melanomacrophage, hepatic fibrosis and congested blood vessels. In addition, the enzyme activity of liver cholinesterase (ChE) was also found to be affected by copper sulphate, as 100% of cholinesterase activity was inhibited at 20.0 mg/L. Thus, liver enzyme activity and histopathological changes are proven to be alternative sources for biomarkers of metal toxicity.

2,4-dinitrophenol (2,4-DNP) is utilized in the production of wood preservatives, dyes, and also as a pesticide. Human acute (short-term) exposure to 2,4-DNP in humans by means of oral exposure are nausea or vomiting, sweating, headaches, dizziness, and weight reduction. Thus, the removal of this compound is highly sought. A 2,4-DNP-degrading bacterium (isolate 1) was isolated from a sample soil from Terengganu. This bacterium (isolate 1) was characterized as a rod Gram positive, non-sporulated, and non-motile bacterium. The bacterium is oxidase negative and had catalase positive activity and was able to grow aerobically on 2,4-dinitrophenol as the sole carbon source. This bacterium showed maximal growth on 2,4-DNP at the temperature optimum of 30 oC, pH 5.0 and was tolerant to 2,4-DNP concentration of up to 0.5 mM (0.092 g/L). This bacterium prefers to use urea as the nitrogen source in addition to yeast extract for mineral source and vitamin precursors.

Cholinesterase (ChE) inhibition and histopathological features of brain tissues of Clarias gariepinus were investigated with a purpose to develop biomarkers for monitoring heavy metals. The effects of cadmium toxicity on were assessed by ChE inhibition and characterisation of ChE by affinity chromatography and histological variations in brain tissues were studied by H&E staining under light microscope.