M74 syndrome and thiamine in salmon broodfish and offspring

The relationship was examined between the occurrence of M74 syndrome (abnormally high yolk-sac fry mortality in the Baltic salmon) and the thiamine (B1 vitamin) concentration in the eggs, liver and white muscle of female salmon broodfish and in the fry. Newly stripped eggs with total thiamine concentrations of ca. 0.35 mg kg–1 or lower were shown to develop into M74 offspring. M74 syndrome was not found to exist in the Teno river Atlantic salmon or in the Daugava river Baltic salmon, but was prevalent in 1994–1996 in the Finnish rivers flowing into the Gulf of Bothnia. This is thought to be a result of the low reserves of thiamine in the broodfish during maturation in these rivers. It was shown that sexual maturation of female salmon broodfish entails the transport of a large amount of thiamine to the ovaries. The total thiamine content of the liver was only a fraction of that needed in the eggs, but white muscle tissue may act as a reserve for this purpose.