posetissue. Meiosisstarts in October-November
and continues for 3–4months.Ripemalesthathave
completed thefirstcycle ofspermatogenesis are
typically 4 years old and 10–15 kg body weight. They
have enlarged white testes containing cysts with dif-
ferentiated spermatozoa (Figure le).Individual cy-
cles are asynchronous in a stock, but the majority of
malesmature fromFebruary to June. In summer,
the unshedspermatozoa andremaining meiotic
cells arereabsorbed(Figure 1f) andonlyprimary
spermatogonia remain in the cyst walls. Elevated
watertemperature(above 15°C)accelerates sper-
matogenesis but induces rapid testicular regression
in the post-meiotic phase.Spontaneousspermia-
tion wasoccasionallyobserved, but for scheduled
spawningspermiation wasinduced bytreatment
with carp pituitary extracts. Males are capable of at
least three consecutive spermiations at biweekly in-
tervals, producing up to 200 ml of milt at each sper-
miation. As inotherAcipenseriformes, white stur-
geon spermatozoa possess anacrosome and under-
go acrosome reaction during insemination (Cherr
&Clark1985).White sturgeon spermcontains the
enzyme amidase,which isassociatedwithsperm
penetration through the egg envelope in non-tele-
ostean vertebrates(Ciereszko et al.1994). How-
ever, the functions of this enzyme and the details of
the acrosomalreaction ininsemination ofeggs in
sturgeon are unknown.
Gonadaldevelopment offemales is long and
asynchronous, relative to individual age and body
size (see ‘Age and body size at puberty’ below). Oo-
cyte meiosis anddifferentiation of the ovarianfolli-
cle start at age 2–3years. Thenarrowovarian
groove(formedonthe lateralside of thegonad)
contains clusters ofoogonia andsmall oocytes sur-
rounded bysquamousfollicularcells(Figure2a).
By age 4–5 yearsgonialmitosisappearscomplete,
and the ovigerous lamellaecontainonly oocytes in
the primarygrowthphase, reaching 100-300 μm
diameter and surrounded by a fewgranulosacells,
PAS-positivebasementmembrane and thethecal
layer. The oocyte cytoplasm is strongly basophilic
and contains unstained spherical vesicles in the cor-
tex. Numerous small nucleoli appear in the periph-
ery of the nucleus (Figure 2b). Oocytes are visible to
the unaided eye as small transparent spheres and10.2and 7.3% forstGTHI.and 9.7 and 6.1% for
stGTHIITestosterone(Gay&Kerlan1978),estra-
diol-17β(England et al. 1974) and17α 20 β-dihy-
droxy- 4 - pregnen- 3 - one (Scott et al.1982)were ana-
lyzed by previouslydescribed RIAprocedures.
Minimumdetectable concentrations for these ste-
roids were 0.52 ng ml-1, 0.13ng ml-^1 , and 0.10 ng ml-^1 ,
respectively.
In the followingdescription of gonadal develop-
ment weapplied theterm ‘puberty’to thegonadal
condition or age of animals that have completed the
firstgonadalcycles. Theterm‘vitellogenesis’was
used to define aperiod ofoocyte growth associated
withdeposition ofyolkplatelets in the cytoplasm.
The threelayers of the oocyte envelope were
termed zona radiatainterna,zona radiata externa
and gelatinous (jelly) coat, following the classifica-
tion of Dettlaff et al.(1993).
Gonadal development and gametogenesisWhilegonadal sexdifferentiation inculturedwhite
sturgeon has not been investigated in detail, our ob-
servations ongonadal development indomestic
(F 2 ) offspring suggestthatanatomical andcytolog-
ical differentiation of sex glands were completed by
the age 18 months, at fork length 58–72 cm and body
weight 1.1–2.3 kg. The females had distinct ‘ovarian
grooves’ on the lateral side of the ovary, with lamel-
lae containing the nests of primary oogonia and the
oocytes in meioticprophase. Thegerminalportion
of the testis was seen as anarrow layer of solid tissue
on the dorsal part of the gonads, containing sperma-
togonia enclosed by a fibrouswall. Thegonads of
bothsexeswerelargelycomposed of adiposefatty
tissuesurrounded by the peritonealepithelium.
Furtherobservations at age 3–4 years,conducted
on hundreds ofmarkedfish onseveral commercial
farms, indicatedthatdomesticoffspring had a1:1
sex ratio.
Full differentiation of testicularfolliclesand pro-
liferation of spermatogonia were observed at age 3
years (Figure la. b), andwerefollowed by meiosis
and spermiogenesis (Figurelc,d). Cellprolifera-
tion was accompanied by theenlargement of the
germinalportion oftestes and by resorption of adi-