Stress-induced water permeability changes in the tropical cichlid, Oreochromis niloticus (Trewavas)

The effect of short-term, experimentally-induced stress on the branchial water permeability of Oreochromis niloticus was studied. Both handling and thermal stress increased water permeability but apparently by different mechanisms. The enhancement of water permeability by acclimation temperatures and acute temperature changes had Q ₁₀ of 3.52 and 2.24 respectively. Environmental sodium concentration and acute hypoxia had no effect while hypercapnia and mild anaesthesia decreased water permeability. Both hypercapnia and mild anaesthesia probably elevated arterial pCO₂ with a concomitant reduction of metabolism.