plasma androgens (Moberg et al. 1995, Cuisset et al. warm water. In the wild, most species of sturgeons
1995). Recently, we demonstrated that the implants reach first sexual maturity at age 10 to 20 years,
of exogenous testosterone in sexually undifferen- while in culture the age interval 3–10 years is most
tiated white sturgeon will significantly elevate the frequently reported. Thus, Acipenseriformes ap-
pituitary concentrations of both stGTHs (Pavlick et pear to have a labile pubertal age that may be influ-
al. 1995). Likewise, pre-vitellogenic females im- enced by environmental factors and growth rates.
planted with testosterone have higher levels of pi- One interesting aspect of oogenesis observed in cul-
tuitary stGTHs than controls. suggesting that the tured white sturgeon was the ability of females to
pituitaries of adult sturgeon are also sensitive to the maintain ovarian follicles in an arrested but ad-
positive feedback of testosterone. This positive vanced previtellogenic state for one or more years
feedback effect of testosterone in sturgeon is com- before the onset of yolk deposition. This suggests
parable to the reported effect of testosterone in that ovarian recrudescence may be affected by
modern teleost species (Crim & Evans 1983). It still some endogenous and exogenous factors, resulting
remains to be determined whether or not testoster- in highly asynchronous female puberty. High varia-
one can also have a negative feedback effect on the bility in ovarian development rates of captive fish
secretion of the gonadotropins and what the poten- may be caused by culture stress and competition re-
tial feedback effects of estrogen are. lated to high rearing densities, commonly utilized
In vitro oocyte maturation is readily induced in on the commercial farms.
white sturgeon by C-21 steroids, with 17α, 20β-Di- Sex-related differences in pubertal age and
hydroxy-4-pregnen-3-one (17α, 20β-Dp) being length of the gonadal cycle were previously report -
most potent (Lutes 1985). Our observations on ov- ed in wild and cultured Acipenseriformes (see Hol-
ulating domestic females showed consistent and
^
cík 1989 for review). Males mature at a younger age
significant increases in plasma concentrations of and usually have annual gonadal cycles whereas the
17 α,20β-DPcorrelated with an increase ofstGTH females mature late and have ovarian cycles lasting
II. Wild-caught pre-ovulatory white sturgeon fe- longer than one year. Estimates of breeding fre-
males also had significantly higher plasma concen- quency in wild sturgeon females range from one to
trations of 17α, 20β-DP, compared to late vitellogen- ten years (Hol^
cík 1989), but these assumptions are
ic females that did not reach the responsive state of usually inferred from the age-body size population
gonadal development (Lutes et al. 1987). Similar structure and the presence of spawning marks on
data were obtained with migratory females of wild finray sections (Roussow 1957). Observations on
Atlantic sturgeon,A.oxyrinchus(Van Eenennaam cultured sturgeon suggest a predominantly biennial
et al. 1996). While the identity of the putative matu- ovarian cycle (Williot et al. 1991, Doroshov et al.
ration-inducing substance (MIS) in white sturgeon 1994). Variations in the length of individual cycles
has not been established, the potential similarity in maybe driven by exogenous (environmental) and
the native MIS between sturgeon and salmonids endogenous (genetic) factors, but the current
(Young et al. 1986) may lend further support to a knowledge of reproductive physiology in Acipense-
generally similar endocrine control of reproduction riformes is inadequate to answer these questions. It
in the Acipenseriformes and modern teleosts. is possible that the length of the reproductive cycle
in wild and cultured sturgeon is labile, as is their pu-
bertal age. However, it is more likely that Acipense-
riformes have developed endogenous reproductive
rhythms of specific duration, as indicated by their
relatively advanced neuroendocrine control of re-
production and the clearly apparent seasonality of
the gonadal cycle. As in teleosts (Bromage et al.
1993). annual photoperiod is likely to control game-
togenesis in sturgeon, although no experimentalConclusionsOur data support several previous studies with Sib-
erian sturgeon and the sturgeon hybrid (H. huso ×
A.ruthenus), which suggested that puberty and sex-
ual maturation of Acipenseriformes are accelerat-
ed by intensive culture utilizing artificial feed and