Figure 3. Total plasma calcium (Ca) concentrations and diameter (ED) of vitellogenic ovarian follicles in eight females repeatedly sam-
pled during the first ovarian cycle. Bars are x ± se. Plasma calcium has a linear relationship with plasma vitellogenin (Ca = 98.94 – 0.015 Vg
μg ml–1), and elevation of total plasma calcium above 100 μg ml–1indicates the presence of vitellogenin (Linares-Casenave et al. 1994).
Inset: SDS-PAGE of plasma from mature male (lane 1), immature female (lane 2). late vitellogenic female (lane 3), purified white
sturgeon vitellogenin (lane 4), and molecular markers (lane 5). Vitellogenic female plasma and purified vitellogenin exhibit two polypep-
tides with an approximate molecular mass of 190 and 210 KDa. Courtesy of J. Linares-Casenave, University of California, Davis.
arepresent in theovarythroughoutconsecutivere-
productivecycles.Asoogenesis advances,some of
the oocyteswillincrease indiameter to400–600 μm
and appear as enlargedtranslucentspheres. Their
cytoplasm is less basophilic andexhibitsvesicular
structure. However, crystalline yolk bodies are not
detectablewith light microscopy(Figure2c). The
distinct features ofthis stage are the appearance of
PAS-positiveenvelope anddifferentiation of the
granulosa cell layer (Figure 2c, inset). Deposition of
crystalline yolk usually follows this stage, but can be
delayed insomefish for one or twoyears. Low con-
centrations of vitellogenin (< 1 μgml–1)are detected
in plasmaofwhitesturgeon atthisstage (Linares-
Casenave et al.1994);morphological evidenceof
endocytosis atsimilarstage was reported inSiber-
ian sturgeon (LeMenn &Pelissero 1991), suggesting
the initiation ofyolk precursor uptake by the oo-
cyte.
Vitellogenic growth of the oocyte starts at age 4–8
years and a bodyweightof15–30 kg, andcontinues
f o r 16–18months.Oocytes increase indiameter
from0.6to 3.5 mm and change in colorfromlight
yellow tobrown,grey, andfinally toblack, due to
synthesis and deposition ofmelanin granules in the
cortical cytoplasm. The crystalline yolkbodiesfirst
appear in theperipheralcytoplasmand,while in-
creasing in size,exhibitcentripetalprogression
(Figure 2d) similar to yolkdeposition in the am-
phibian oocyte (Dumont 1972). Gradually, the yolk
platelets and oil globulesfill theentirecytoplasm
except for the perinuclear area. When vitellogenic
growth subsides(diameter>3 mm), theoocyte un-
dergoes major cytoarchitectural changes and be-
comes ovoid in shape with a slightly pointed animal
pole. Thegerminalvesiclemigrates to the animal
pole and thelargeyolkbodies and oilglobules ag-
gregate in the vegetal hemisphere (Figure 2e, vege-