author(s)
Jayakumar N and Subburaj A

abstract
RThe present study aimed at assessing the sublethal (SL) toxicity of the heavy metal, Cadmium in the freshwater Asian Stinging Catfish, Heteropneustes fossilis. The SL toxicity test concentrations were selected based on the reported acute toxicity test value (44.13 mg/l). The concentrations selected were 1.11, 2.21, 4.41, 8.82 and 17.64 mg/l. At the end of the experiment (14th and 28th day), live fish samples were collected from the middle (4.41 mg/l) and last (17.64 mg/l) concentrations, sacrificed and their gill, liver and kidney were excised out and fixed in Bouins fixative for 24 hrs. Later, standard histology protocol was followed to study the histological alterations in the gill, liver and kidney of the fishes exposed to SL concentrations of Cadmium. The most common histopathological alterations in the gills of fish exposed to Cadmium were characterized by erosion of secondary lamellae, lamellar fusion, shrinkage of blood vessels, secondary lamellar damage, hyperplasia, vacuolation, epithelial lifting, and shortening of secondary lamellae. The histological changes observed in the liver of fishes exposed to Cadmium included rupture of hepatocytes, vacuolation, hemorrhage in liver sinuses, cellular necrosis, increased pycnotic nucleus, melanomacrophages. In the present work, histological changes like melanomacrophages, degenerated glomerulus, increased peritubular space, shrunken glomerulus, loss of cytoplasm, vacuolation, increased periglomerular space were observed in the kidney of the fishes treated with Cadmium. Thus the present investigation has proved that Cadmium is a potential heavy metal toxicant affecting the fishes at tissue level even at low concentrations, which might in turn affect the physiological processes in the long run.