Toxicopathological impact of sub-lethal concentration of lead nitrate on the aerial respiratory organs of ‘murrel’ channa striata (bloch, pisces)
Main sources of lead pollution of aquatic ecosystems are the industrial discharge, atmospheric fall out and sewage effluents. Toxicity of lead in the lung-breathing animals is generally manifested through the contaminated air. In fish, the toxicity of lead is however induced via the gills, which are their main respiratory organs. Keeping this in mind, the gills have widely been used as bio-indicator not only to detect lead toxicity (Parashar and Banerjee, 2002) but also for analyses of several other pollutants (Nath et al., 1989; Munshi and Singh, 1992; Chandra and Banerjee, 2004). Many of the fishes in the Indian subcontinent have developed a bimodal respiratory mechanism for exploitation of water (through their gills and highly vascularized skin) as well as air (through air-breathing organs, ABOs). These ABOs in fishes are analogous to the respiratory organs of the tetrapods. Although in many airbreathing species (for e.g. H. fossilis and C. batrachus), aerial respiratory organs are modified gill structures, the ABO in Channa striata, an important edible fish, is made of a pair of suprabranchial chamber, which develops dorsal to the gill arches. The outer surface of the suprabranchial chamber in this fish gets highly vascularized for absorbing atmospheric oxygen. In this paper the attempts have been made to use the air-breathing organ (ABO) of C. striata as a potential bio-indicator of the contaminated waters. Several researchers have investigated the functional anatomy of the ABOs of different species of Channa with respect to their gross anatomy (Liem, 1984), ultrastructure (Hughes and Munshi, 1973) and surface architecture Hughes and Munshi, 1986). According to Munshi, (1962), the suprabranchial chamber of Channa (=Ophicephalus) is not a waterproof compartment and remains in free communication with the pharynx. The ABO of C. striata therefore faces the contact stress of the environmental hazards, hence needs proper investigation.