SHORT-TERM EXPOSURE TO ACID WATER IMPAIRS OSMOREGULATION, SEAWATER TOLERANCE, AND SUBSEQUENT MARINE SURVIVAL OF SMELTS OF ATLANTIC SALMON (SALMO-SALAR L)

Smelts from several stocks of Atlantic salmon were released in the est uaries of, and 5 km upstream in, an acid river and a neighbouring lime d river in southern Norway. There was good agreement between recapture rates of released smelts and physiological effects and mortality of f ish retained over the same period in floating cages at the different r elease sites. Of the smelts released upstream in the acid river, scarc ely any were recaptured as adults. The smelts retained in the cages in this river suffered from severe osmoregulatory failure and high morta lity within a few hours. Gill Na+,K+-ATPase activities were significan tly reduced. Exposure for a few hems to the acid river impaired the se awater tolerance of the the fish. The results suggest that simple phys iological challenge tests of smelts after exposure to the water in whi ch they are to be released may be a useful tool for predicting surviva l after release, and may help decide when and where smelts should be r eleased.