Tolerance to acid water among strains and life stages of Atlantic salmon (Salmo salar L.)

Reintroduction of Atlantic salmon (Salmo salar L.) after liming of acidifie d barren salmon rivers could benefit by choosing acid tolerant strains. Tes ting different life history stages from fry to smolts of five salmon strain s with different acidification history demonstrated strain-specific variati on in tolerance to acid aluminum-rich waters for stages from fry to parr. C ontrary to expectation, salmon from non-acidified rivers were more tolerant . Differences in sensitivity were found between life history stages. Within a specific life history stage, size-dependent sensitivity was found; small fish being more sensitive to pH while large fish were more sensitive to al uminum. Presmolts showed the same relative tolerance between strains as you nger stages. These differences disappeared, however, when the smolt reached fall smoltification, probably due to supersensitivity at this stage. Poor water quality during the last period of smoltification and outmigration can thus mask the genetic potential for tolerance to acidic rivers.