Reconditioning of sea-run Baltic salmon (Salmo salar) that have produced progeny with the M74 syndrome

Sea-run Baltic salmon of the Swedish Dalälven population were subjected to 2 different reconditioning studies in order to determine possibilities to cure the M74 syndrome; namely to produce alevins without M74 mortality. Reconditioning of female salmon was achieved both by feeding and by thiamine injection. In the first experiment, spawned female salmon were given a commercial brood-fish feed until renewed maturation, when they were stripped. The eggs were fertilized with milt from sea-run males. Eggs and alevins were followed to the fry stage. In the second experiment, ascending females were injected with thiamine 1 month before maturation and stripped. Eggs and alevins were handled in the same way as in the first experiment. Feeding sea-run salmon was troublesome and only 13 females accepted dry food. These females improved the thiamine status of their egg tenfold. Thiamine injection of females was also effective, and the thiamine content of their eggs increased by a factor of 13. No M74 mortality was observed in the offspring of female salmon that were reconditioned. Activity of the hepatic enzyme CYP4501A in salmon alevins seemed to vary with thiamine content and was induced pre-hatch in both M74 alevins and healthy alevins of females reconditioned by feeding, indicating that a good thiamine status is more essential than the burden of xenobiotics.