Figure 5.The age and body size at puberty in cultured white stur-
geon females. Data are pooled observations on the broodstock
of five commercial farms(N=184).
layer(Figure2c)persisted over a period of 1–3 years
before the initiation of yolk deposition. The reab-
sorption of previtellogenic follicles and develop-
ment of new oocytes could potentially occur within
the annual sampling interval, but no atretic follicles
were observed on the histological slides from any of
these fish.
Observations on the second ovarian cycle in re-
peatedly spawned females(n=5) revealed a bien-
nial cycle, with three of these fish spawningonodd
years, 1991 and 1993, and two on even years, 1992
and 1994 (Figure 4). All fish started the second vitel-
logenesis during the first fall after spring spawning,
and their oocytes reached the late phase of vitello-
genic growth in the fall of the following year. They
were spawned a second time during a period from
March to June, and the calendar date of the second
ovulation in individual females was very similar to
that of the first spawning.
These preliminary observations reveal annual
testicular and biennial ovarian cycles in cultured
white sturgeon. Gonadal development in both sex-
es exhibits seasonal patterns, with testicular meiosis
and ovarian vitellogenesis starting in the fall, and
final gonadal maturation completed during the
spring. The observations onseasonal changes in thepituitary and plasma concentrations of two stur-
geon gonadotropins (Moberg et al. 1995) also re-
vealed that gonadal cycles in white sturgeon are
controlled by seasonal factors.Age and body size at pubertyMost (80–90%) cultured white sturgeon males
reach puberty at age 3–4 years and body weight of
7–14kg. In commercial farms, sturgeon males are
selected for spawning from the production stock at
age 4 years and body weight 10–15kg. In the wild,
white sturgeon males reach puberty at age 10–12
years, and body weight of approximately 12 kg
(PSMFC^1 ).Thus, the body size at first sexual matu-
rity appears to be similar in wild and cultured males,
but the latter reach puberty at a younger age.
Cultured females reach puberty at an age from 6
to 14 years, with fifty percent maturing by age8,at a
mean body weight of 32 kg and a mean fork length
of151 cm (Figure 5). These data are based on a large
numberofgravid females pooled from different age
cohorts raisedonfarms, and the maturation rates
may be affected by farm husbandry and the age
groups life history. However, the proportions of
mature females within each age group showed very
similar trends (Doroshov et al. 1994, Logan et al.
1995). The body weight of females that completed
their first sexual maturation was highly variable, 32
±10kg(× ±sd, range 12–61kg). Similar variability
was found in wild-caught females used for farm
spawning during the past four years (36 ± 13 kg, n =
43),although the age and iteroparity of these fish
could not be examined. The smallest mature wild
female weighed 12 kg, and the largest ‘virgin’ fe-
male caught in San Francisco Bay (stage similar to
Figure2a)weighed 53 kg(S.Doroshov unpublished
observations). A recent report indicates that the
pubertal age of wild white sturgeon females ranges
from 15 to 32 years (PSMFC^1 ). This suggests that a
highly variable pubertal age and body size in cultur-
ed sturgeon may reflect the patterns existing in nat-
ural population. However, cultured females reach
puberty at a considerably younger age compared to
wild fish. Similar observations were reported for