Ultimobranchial gland of a freshwater teleost, Heteropneustes fossilis, in response to cadmium treatment.

Heteropneustes fossilis were subjected to 288 mg/L (0.8 of 96 h LC(50)) and 72 mg/L (0.2 of 96 h LC(50)) of cadmium chloride for short-term and long-term experiments, respectively. After sacrificing the fish, the blood was collected on 24, 48, 72, and 96 h in short-term and after 7, 14, 21, and 28 days in long-term experiment and analyzed for plasma calcium levels. Also, ultimobranchial glands were fixed on these intervals. The plasma calcium levels of short-term cadmium-exposed fish remain unchanged after 24 h. The levels exhibit a progressive decrease from 48 h onwards. The fish exposed to cadmium for 7 days exhibit a decrease in the plasma calcium level. Thereafter, the levels progressively decrease till the end of the experiment (28 days). Up to 72 h exposure of the fish to cadmium, the ultimobranchial gland exhibits no histological change. After 96 h, a decrease in the staining response of the cytoplasm of ultimobranchial cells has been noticed. The nuclear volume of these cells records a slight decrease. Up to 14 days of cadmium exposure, there is no change in the histological structure of ultimobranchial gland. After 21 days following the exposure, the ultimobranchial cells exhibit a slight decrease in the staining response of the cytoplasm and the nuclear volume of these cells records a decrease. Following 28 days cadmium exposure the nuclear volume exhibits a further decrease, and degeneration and vacuolization sets in.