The Baltic salmon in battle with pollutants and disease. / Östersjölaxen i kamp mot miljögifter och sjukdom.

The Baltic salmon has during the latter part of the 20th century been subjected to several threats. Most notable have been the high levels of contaminant release and a disease that causes early life mortality of the young. Ever since utilization of water power from the Swedish rivers began in the 1940ies, thus deminishing the natural breeding areas for the salmons, an extensive hatchery program has compensated for the loss and, generally, increased the salmon populations in the Baltic Sea but simultanously decreased the genetic variation. In the 70ies a disease appeared in the hatcheries, causing high mortality (up to 95%) of the salmon fry. The explanation for this devastating syndrome, known today as M74, has not been found but it has been suggested that the high load of persistent environmental pollutants like PCB and dioxin that historically has been released into the water systems, have contributed to the problem. Since these chemicals strongly resemble endogenous signalling substances -hormones- exposed individuals experience altered cellular signalling which eventually results in cell death. This signalling is mediated by a receptor protein known as the aryl hydrocarbon (Ah) receptor which during recent years has been subjected to much interest because of its role in mediating toxicity of several environmental pollutants. Further research on the Ah receptor may in the future bring greater understanding of some the problems that the Baltic salmons presently are suffering from.