[Probe (1990): (XXIX), 3, 220-228] Protective Role of Liv.52 Against Histological Damage due to CdCl 2 Toxicity in the Intestine of Teleost Fish Suresh Kothari, Bhaskar Reddy, P. and Rathore, H.S. School of Studies in Zoology, Vikram University, Ujjain, India. ABSTRACT Fresh water catfish Mystus tengara (Ham.) were experimentally exposed to sublethal concentrations of CdCl 2 for 30 days, to assess the structural changes in their intestines and the role of an indigenous drug Liv.52 in preventing such changes. The water quality and feeding behaviour of fish were also studied. Cd poisoning resulted in cell death and necrosis in the columnar epithelial cells at the tips of the villi in the anterior and posterior intestine, respectively. Liv.52 was found to play a protective role against the structural damage in the Cd-exposed fish intestine, while its administration in the absence of Cd resulted in a very healthy and hyperactive condition of the intestinal tissues. Changes in the physico-chemical characteristic features of water were noticed due to Cd contamination. Behavioural studies revealed that Cd adversely affected the feeding behaviour of the fish, whereas Liv.52 greatly enhanced the feeding activity of the experimental fish indicating that Liv.52 provided protection to the fish intestine against CdCl 2 toxicity. INTRODUCTION Cadmium is a potentially hazardous pollutant in the environment. The methods for the passage of metal ions across the surface of intestinal and other biological membranes are well reviewed (Stein, 1967; Skoyma and Waldron, 1971). Cd toxicity in fish has been reported to depend on water quality criteria (Eisler, 1971; Slobe and Flook, 1975; Pascoe and Cram, 1977; Calamari et al., 1980). Toxic effects of Cd with different concentrations and duration of exposure are well documented in teleosts (Nakamura, 1974; Voyer et al., 1975; Dubale and Shah, 1979; Singh and Sivalingam, 1982; Stromberg et al., 1983; Kothari and Saxena, 1988) and in other animals by Friberg, 1977. Chemical symptoms of Cd toxicity are well documented (Browning, 1969). Absorption and accumulation of Cd in the digestive tract have been described in fish (Edgren and Notter, 1989; Kumuda et al., 1980) and in mammals (Venugopal and Luckey, 1975). Studies on the protection of mammalian organs against a wide variety of toxicants with an indigenous drug Liv.52 have been conducted in the past (Rao, 1985; Prasad, 1975, 1976; Joglekar et al., 1963; Patel and Sadra, 1963). Such protection studies in fish are wanting. Recently, Rathore and Rawat (1989) have reported that Liv.52 could protect against Cd-induced histological changes in mouse gut. With this background the present study was undertaken to find out whether Liv.52 could provide protection to fish organs against CdCl 2 intoxication. The present paper deals with the histopathology and protective role of Liv.52 in the Cd-exposed intestine of fresh water teleost Mystus tengara (Ham.).