Triploid female fish are unlike normal diploids in that they show impaired oocyte growth and are unable to produce viable offspring. Compared to diploid siblings,
triploid female brook trout (Salvelinus fontinalis) have significantly lower levels of plasma
vitellogenin,
testosterone (T), and
estradiol-17beta (E(2)), and show significantly lower gonadosomatic indices. The purpose of this study was to compare in vitro
steroid production by diploid and
triploid ovarian follicles in order to determine whether delayed oocyte growth in
triploids is the result of a decreased capacity for E(2) synthesis by
triploid follicles. Intact oocytes (i.e., including follicular tissue) from several age 3(+)
triploids were pooled and sorted according to small (<2mm), medium (2.2-3.0mm), and large (4.0-5.0mm) diameter size, and compared to same-sized vitellogenic oocytes from 3(+) diploids. Oocytes were incubated for 8h at 15 degrees C in the presence or absence of
gonadotropin stimulus (SG-G100) and the precursors E(2), T, and
cholesterol.
Estradiol-17beta output following
SG-G100 treatment was significantly higher than in controls for both diploid and
triploid follicles. Production of E(2) was dependent on stage of oocyte and follicular development in
triploids, with
triploid and diploid follicles of similar diameter producing similar amounts of E(2) with
SG-G100 stimulus. This suggests that ovarian steroidogenesis is similar in diploids and
triploids.