FRESHWATER ADAPTATION IN THE EURYHALINE TELEOST, CHELON-LABROSUS .2. EFFECTS OF CONTINUANCE OF ADAPTATION, CORTISOL TREATMENT, AND ENVIRONMENTAL CALCIUM ON WATER INFLUX IN ISOLATED GILL

The effects of freshwater adaptation duration, cortisol, and environmental calcium on water influx in isolated gill of the thick-lipped gray mullet, Chelon labrosus, were studied using an in vitro technique. An estimation of the water permeability and the osmotic permeability coefficient in this euryhaline fish was made from the rate of weight increase in isolated gills immersed in deionized water after preincubation in saline solution. The water influx in the isolated gills and/or permeability is reduced progressively with the adaptation to fresh water in C. labrosus. Cortisol increases the water influx and/or water permeability only in seawater-adapted fish. An increased calcium content of fresh water reduces the weight increase of isolated gill. These results are in accord with the osmoregulatory performance characteristic of this fish. © 1979.