Stress indicators at cellular and tissue levels have been developed in fish and other aquatic organisms in the recent past to monitor environmental contamination (Al-Ghais and Ali, 1999, Al-Ghais et al., 2000, Lam and Gray, 2003, Facey et al., 2005, Mdegela et al., 2010 and Stoliar and Lushchak, 2012). Tissue cholinesterases and non-protein reduced glutathione (GSH), which protects cell against oxidative injury and detoxicates xenobiotics and/or their metabolites, have been validated

as pollution biomarkers in fish and other aquatic animals (Otto and Moon, 1996, Al-Ghais and Ali, 1999, Lam and Gray, 2003 and Stefano et al., 2008). Recently, attempts

GSK1120212 made to investigate cholinesterase/AChE activity in fish tissues as early-warning biomarker for the assessment of pollution in ponds/lakes receiving sewage wastewater revealed site- and tissue-specific variations AZD2281 molecular weight in AChE responses (Lopez-Lopez et al., 2006 and Mdegela et al., 2010). Moreover, organ-level biomarkers, liver size (hepatosomatic index, HIS) and macrophage aggregates in the spleen of rock bass, were found to be useful in monitoring harbor contamination with the effluent from sewage treatment plant (Facey et al., 2005). However, much less is known about the responses of cellular biomarkers to aquatic environment contamination with sewage and their potential usefulness in monitoring the depuration of marine organisms grown in the sewage-fed aquaculture.

The current study was, therefore, undertaken to evaluate the of status of cholinesterase(s) active towards acetylcholine, referred to as AChE (Siva Prasada Rao and Ramana Rao, 1984 and Rodriguez-Fuentes and Gold-Bouchot, 2004), and non-protein before GSH in the liver and muscle, and hepatosomatic index in Mozambique Tilapia (Tilapia mossambica, Peters), a commercially important and relatively resistant species well adapted to grey water aquaculture ( De Silva et al., 2004), exposed to fresh water, treated sewage water and follow-up depuration in fresh water in order to validate these cellular biomarkers for monitoring the potential fish toxicity that may be caused by culturing the fish in treated sewage water and the effectiveness of depuration process in sewage-fed aquaculture. Acetylthiocholine, thiocholine, Ellman’s reagent (5,5′-dithio (2-nitrobenzoic acid), DTNB), reduced glutathione (GSH), bovine serum albumin and (Tris[hydroxymethyl]aminomethane) were obtained from Sigma Chemical Co., a division of Sigma–Aldrich Corporation, USA. Samples (n = 16) of T.