Induced vitellogenesis in triploid coho salmon ( Oncorhynchus kisutch)

Small numbers of post-meiotic cells are produced by triploid salmonids. These develop to the mature stage in males (i.e., functional spermatozoa), but not in females. The aim of the present study was to examine whether impaired estrogen biosynthesis might be the cause of the lack of full maturation of post-meiotic oocytes in triploid females. Vitellogenesis was induced in immature diploid and triploid coho salmon (Oncorhynchus kisutch ). Plasma vitellogenin levels were significantly higher in 17 beta estradiol (E sub(2))-injected fish than in sham-injected fish. There was no significant difference between triploids and diploids for the levels attained. E sub(2)-injected fish had significantly higher hepatosomatic indices and pituitary gonadotropin content than sham-injected fish by 4 weeks after the first treatment. These data suggest that the post-meiotic growth of oocytes in triploids is impaired due to an absent or diminished estrogen stimulus from the ovary on hepatic vitellogenesis.