Responses of gill to various changes in salinity in fresh water teleost Colisa fasciatus (Bl. and Schn.).

In the present study the effects of different osmotic conditions have been observed on the gills of a fresh water air breathing teleost Colisa fasciatus. 1. In control fishes two types of specialised cells (mucous gland and mast cells) are found in the gill. There is no special type of "chloride cell". None of the cells give AgNO3/HNO3 test. The size of the mucous cells varies from 5.50 micrometer to 5.94 micrometer. 2. After distilled water treatment, the epithelium is severely swollen and at some places completely desquamated from the lamellae, leaving only the blood capillaries and supporting pilasler cells, due to endosmosis. 3. After 40% salt water treatment the exhaustive stages in mucous glands and marked shrinkage of the entire respiratory epithelium is observed. The excess of salt causes exosmosis resulting in death of the fishes. 4. After 8% salt water treatment the number and the size of mucous prodicing cells of treated fish increases approximately four times as compared to controlled fishes during the first week of adaptation. In case of one month treated fish the gill surface area increases extensively and is occupied by the mucous cells. These mucous producing cells are AgNO3/HNO3 positive indicating their transformation into so called "chloride cells". The size of mucous cell increases upto 19.63 micrometer.