Table 1.Results of attempts tospawnwildcaughtfemales ofAcipensersturio(1981–1994).I9811983
1984
The only female ovulated, but due to over-maturation, the quality of eggs was poor. Nearly 700 embryos hatched, but only ten
survived the first month of rearing after which rearing was discontinued.
The two females did not ovulate, probably because of under-maturation
The PI of eggs of theonlycapturedfemales did notdecrease by 6 days afterstocking; theeggsbecamesofter andmoredelicate
as probable expression of damage. Became male A. sturio were not available simultaneously we attempted hybridization of A.
sturiowith Siberian sturgeon A. baerii, but ovulation and spermiation were poor, and only a few abnormal embryos hatched
and diedquickly.
The two femalesovulatedperfectly, and the fertilizationrate wasclose to 80% inbothcases;incubationlasted 4.6days and
meanhatchingsuccess was80%, but allfreeembryosdied.
The firstfemale was weakand lacked theability toreproduce(GVBD = 0). Itdied 2dayslater andautopsyshowedfatty
gonads. asign ofunder-maturation. Asecondfemale,caught verylate, hadalreadyspawned.
The reproductive potential of theonlyfemale was low(GVBD = 9%)without anychange in oneweek.Hormonalstimulation
at a rate of 0.6 mg kg–1( 12% of the normal dose used for reproduction) increased the sensitivity of eggs (GVBD = 63%), but at
too a low level to expect successful reproduction (Williot et al. 1991). Sentivity (GVBD) decreased two days after to only
23%. New hormonaltreatment did notimprove thephysiologicalcondition of thisfemale.
The only female caught was notmature.I985I98619871988June; theonlyfishcaughtlater was a female that the Gironde Estuary does not seem to have
had already spawned.Mostcatches(68%) took changedsince Magnin(1962). He reported that
placefromearly May to 15 June.Half of the fish 78% of thespawningfishwere caught in May and
were caught in theGaronneRiver, one thirdin the firsthalf ofJune; we caught 68%during that period.
DordogneRiver(moreconcentrated in thelower Our age estimates arevery close tothose of the pre-
part), and therest in theGirondeEstuary. One male viouslystudied stock in theGuadalquivir River
was caughtthreetimes(1981,1984, and1987), al- (Spain, see Classen1944), withsomefishbeing ol-
ways in theDordogneRiver. Of thefishcaught in derthanthose of theRioniRiver (Georgia, see Ni-
the GirondeEstuary, none was suitable forrepro- nua 1976).
duction,because the inales and onefemalewere im-
mature and the second female had already
spawned. Artificialreproduction
Femalesweighedalmosttwice asmuch as males
(41.6 kg and23.7 kg,respectively) andfemales aver-
aged 30 cm longer than males (193 cm and 163 cm
respectively).Assumingthat the age-sizerelation-
ship established byRochard &Jatteau(1991) is val-
id for thesefish, weestimated theminimummean
age (using meanTL) to be 10 and 15years formales
and females,respectively.
The upstreammigrationperiod ofbroodfish in
From 1981 until1994, wecollected 1 0 females for
artificial collection ofeggs(Table 1 ). Only 20% (n =
2) of the females showed anoptimalphysiological
state, theothersbeingunder-mature orover-ma-
ture. We rarely had bothsexes simultaneously. Al-
so, we collectedonly fivematuremales (Table 2).
We inducedsuccessfulovulationonly when fe-
inaleswerecaught in anoptimalphysiologicalstate.Table 2.Results of attempts tospawnwildcaughtmales ofAcipensersturio(I981–1987).1981
19851987Both males yielded sperm after 9 and 6 days of stocking, respectively (even one that was not running upon arrival).
Two malesyieldedsperm 3 and 4weeksafterstocking, but onlywith twohormonalinjections at 12hourintervals and atrates
of 20% and 100% of the normal dose, respectively.
One maleyieldedspermafter 4weeks ofstocking(oneinjection)and,anotherone, in poor conditionupon arrival, did not
yield any sperm 6 days after stocking. Between 1981–1994 it seems that the quality of spermatozoa became poorer, as mea-
sured by itsmotility inwater