Estimation of zinc chloride contamination by histopathological analysis of the respiratory organs of the air breathing ‘murrel’ Channa striata (Bloch, 1797) (Channiformes, Pisces)

Sub-lethal toxicity of zinc chloride (11.5 ppm) on the respiratory organs of the Channa striata has been analysed. The mucous cells show periodic fluctuations in their number, size and staining properties elaborating larger quantities of sulphated mucopolysaccharides. The respiratory epithelium (RE) of the respiratory (secondary) lamellae (SL) of the gills shows periodic lifting with deformity of the lamellar elements, haemorrhages due to necrosis and sloughing off of the RE, followed by hyperplasia and fusion of neighbouring SL. Other prominent alterations include increased thickness of the RE and subsequent dismantling of the vascular elements. Fusion of SL reduces the surface area for gaseous exchange, causing impaired branchial respiration. The alterations in the suprabranchial chamber include protrusion of RBC-engorged minute vascular papillae on the floor of its lumen. This brings the blood nearer to the air in the lumen. Congestion of the sub-epithelial blood vessels of the respiratory organs, especially the suprabranchial chamber, takes place following exposure.