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

Sea-run Baltic salmon of the Swedish river Dalalven population were subject ed to 2 different reconditioning studies in order to determine possibilitie s to cure the M74 syndrome; namely to produce alevins without M74 mortality . Reconditioning of female salmon was achieved both by feeding and by thiam ine injection. In the first experiment, spawned female salmon were given a commercial brood-fish feed until renewed maturation, when they were strippe d. 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 a nd 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. Thes e females improved the thiamine status of their egg tenfold. Thiamine injec tion 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 C YP4501A in salmon alevins seemed to vary with thiamine content and was indu ced pre-hatch in both M74 alevins and healthy alevins of females reconditio ned by feeding, indicating that a good thiamine status is more essential th an the burden of xenobiotics.