Branchial Na+K+-ATPase inhibition in a freshwater euryhaline teleost, tilapia (Oreochromis mossambicus), during short-term exposure to toluene or naphthalene: Influence of salinity

The inhibition of branchial Na⁺K⁺-ATPase activity in tilapia, Oreochromis mossambicus, during short-term exposure to toluene or naphthalene at their lethal concentrations was more extensive in salt water than in fresh water. This effect of salinity was seen in fish preacclimated to salt water of 35‰ S before the hydrocarbon exposure at the same salinity, as well as in freshwater acclimated fish exposed to the pollutants in salt water of 20‰ S. The pollution-stressed fish showed a reduced ability to increase the activity of this enzyme on subsequent transfer to salt water of 20‰ S. This greater enzyme inhibition in salt water probably contributed to the higher pollutant-induced mortality in these fish.

Significant (p < 0·05) in vitro inhibition by a relatively high concentration of 10μM of toluene, or naphthalene, was observed in the enzyme activity from both freshwater- and saltwater-acclimated tilapia.