Abstract
The reproduction of artificially induced triploid rainbow trout was histologically and endocrinologically examined during three consecutive seasons. The gonadosomatic indices of triploid females were much lower (0.02-0.06) than the indices of diploid females. The concentrations of sex steroid hormones, including testosterone, estradiol-17β, and 17α, 20β-dihydroxy-4-pregnen-3-one, were much lower than those of diploid females but had small changes, and changes of gonadotropin (GtH) levels in the serum of triploid females differed from those of diploid females. Oogenesis in the triploid ovary was substantially delayed, and most germ cells ceased to develop at the synaptic stage of the first meiotic division. At three years old, various developmental stages of oocytes were detected in the ovary, such as peri-nucleolus, yolk vesicle, and early yolk globule stage. It seemed that these rare developments of triploid oocytes were related to the small increases of steroid hormone concentrations and rise of GtH level that appeared when fish were two years old and three years old. Nevertheless, even in triploid ovarian oocytes grown to secondary yolk globule stage, the germinal vesicles did not migrate and there was no ovulation. It was confirmed that triploid liver cells possessed the potential to produce vitellogenin. These results suggest that the genital gland of triploid females is undeveloped because the odd number of chromosome sets causes the first maturation division to fail, and the endocrinological abnormality.
