Physiological effects of freshwater bathing of Atlantic salmon (Salmo salar) as a treatment for amoebic gill disease

The physiological effects of bathing marine net-pen reared Atlantic salmon with freshwater the treatment for amoebic gill disease (AGD) in Tasmania was evaluated. Acute exposure of AGD affected salmon to hyperoxic freshwater for at least 2 h resulted in a decrease in gill succinic dehydrogenase activity and increases in the total number of mucous cells on the gills. Plasma ions, respiratory and acid-base variables were unaffected by acute hyperoxic and normoxic exposure. Thus, it was concluded that freshwater bathing as a treatment for AGD poses little risk of side effects, but also no benefit with regard to the physiological status of the salmon. Reduced gill enzyme activity may restrict prolonged bathing times, suggesting that care should be taken to ensure that the hyper-ionoregulatory capacity of the salmon is not compromised. (C) 2001 Elsevier Science B.V. All rights reserved.