Reproductive disturbances in Baltic fish: A synopsis of the FiRe project

Research within the Swedish FiRe project Reproductive Disturbances in Balti c Fish has focused mainly on the M74 syndrome, which has caused high mortal ity in fry of sea-run Atlantic salmon (Salmo salar) from the Baltic Sea. At the end of the 4-year project, the cause of M74 is still not known, but th e symptoms have been well described and treatment with thiamine (vitamin B- 1) has been found to cure afflicted fry. The M74 syndrome shows great simil arities to Early Mortality Syndrome (EMS) in salmonids from the North Ameri can Great Lakes. Both M74 and EMS are characterized by a diet-related defic iency of thiamine in fry and broodstocks. A combination of factors may cont ribute to M74, e.g. the diet of salmon in the Baltic Sea, the content of th iamine or thiaminase (an enzyme that degrades thiamine) in their prey fish, ecological changes in Baltic Sea food chains, and pollutants. The few rema ining wild, naturally spawning populations of Baltic salmon are at great ri sk of extinction, as there is no practical method of treating them with thi amine to prevent M74, and they are subject to heavy fishing pressure in the Baltic Sea. A reproductive disturbance similar to M74 occurs in Baltic sea trout (S. trutta), although at lower frequencies than in salmon. The M74 s yndrome does not occur in Baltic cod (Gadus morhua), whose reproductive suc cess is impaired mainly by poor oxygen conditions in its deepwater spawning grounds, in combination with heavy fishing pressure on large cod.