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Fecundity is quantified as the number of vitellogenic oocytes per female
(actual fecundity) from the mean volume of oocytes and the volume of the ovary in
each female. Oocyte volume (OV) was calculated assuming a spherical shape [OV=
(4·p·R3)/3] and averaged. The gonadal fluid that solidifies during fixation occupies
approximately 15% of the ovary as it was estimated by Ramirez-Llodra et al. (2002)
for Porcellanasterid asteroids and corroborated in this study with species from the
families Asteridae, Astropectinidae, Brisingidae, Echinasteridae, Goniasteridae, and
Poranidae. This percentage was subtracted from the total gonad volume.
Fecundity was estimated as follows: V g = volume of the gonad
V pvo = mean volume of a previtellogenic oocyte
V vo = mean volume of a vitellogenic oocyte
N pvo = previtellogenic oocytes counted in a subsample of 100 oocytes per gonad
N vo = vitellogenic oocytes counted in a subsample of 100 oocytes per gonad
P = ratio between previtellogenic and vitellogenic oocytes): P = N pvo / N vo
Assuming that P in a subsample of the gonad is the same as P in the whole ovary, then
P = N pvo / N vo = F pvo / F vo ; F pvo = P x F vo (1)
Where F pvo and F vo are the total number of previtellogenic oocytes and vitellogenic
oocytes, respectively.
The volume of a gonad is equivalent to the number of oocytes multiplied by their
volume:
V g = (V vo x F vo ) + (V pvo x F pvo ) (2)
Replacing F pvo in Eq. 2 with its definition from Eq. 1 we get:
V g = (V vo x F vo ) + (V pvo x (P x F vo ))
V g = F vo x (V vo + (V pvo x P))
F vo = V g / V vo + (V pvo x P) (3)
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