as occurred in1985. In thecase ofimmaturefish, it mate age of 3weeks.Some hadstarted to feed, but
was difficult orimpossible tobringthem intorepro- live food (cladocerans) obstructed thedigestive
ductive condition. Thisalso hasbeen reported for tract.causingdeath.
A. stellatus,a species forwhichDettlaff & Davydo- In the future itwill benecessary to selectdigest-
va (1979) show thatgood reproduction can be ible preyspecies available inlatespring in large
achievedwhenfish are held for fewerthanfour quantities (oreasy toproduce)with anappropriate
clays. In contrast, Doroshov & Lutes (1984) size (worms,insectlarvae.smallcrustaceans). In
achieved goodresultswith wildfemales ofA. trans- massrearing, thisprocedure istime-consuming,
montanusheld up to 4months. It is important to costly, and canintroducepathogens.Specificwean-
ascertainwhether thesedifferences are species-spe- ing practicewithinertfood is alsoneeded,even
cific or due to ourprocedures. thoughthat is far moredifficultthan forotherstur-
The physiologicalcondition ofmalesappears to geonspecies(Monaco et al.1981,Dabrowski et al.
be deteriorating as spermatozoa areincreasingly 1985,Giovannini et al.1991). Theimposed experi-
non-motile. Thepossibleinfluence ofcadmium on mentalwatertemperature(17° C ) wasslightly lower
spermatogenesisshould be explored as some pollu- than in therivers at the time ofcapture.Also, it has
tantsdisturb thereproductivecycle(Billard & Gil- beenshown forteleostspecies such asDicentrar-
let 1984).Second samples ofsperm may be obtain- chuslabrax,Saprusaurata(Barnabe1989) and Co-
able frommalesthree tofourweeksafter capture. regonus lavaretus (Champigneulle 1988) that better
That hasbeen achievedwith a twohormonalinjec- rearingoccurs atwater temperatureshigherthan
tion procedure (instead ofone),consistingrespec- that ofspawning. For boththesereasons, thevalue
tively of 20% and100% of thenormaldose (2 mg of higher rearingtemperatures(22–24°C)should
kg–1) of carphypophysispowder at a 12hour inter- be tested onA. sturio.
val, thefishbeing held at the samewater temper-
ature. Because females and males arc seldom
caught simultaneously, itwould be useful to confirm
whethersuch a process could beimproved by ap-
propriatemanagement ofwatertemperature (Ka-
zanskii1981).Also, it isnecessary toevaluatelong
term preservation ofA. sturiosperm, as has been
donewithseveralothersturgeonspecies(Cherepa-
nov et al. 1993,Drokin et al.1993).Using sperm
from severalmaleswould alsoincrease genetic het-
erogeneity of theoffsprings. Although we found
that hybridization between A. sturio andA. baerii is
possible,furtherinvestigation isneeded to con-
clude if the non-viable embryosobtainedwere due
to the poorquality of thesexualproducts, or to ge-
neticincompatibility.
Adaption of wild immature sturgeon to farm con-
ditionsWe caught 20largejuvenilesfish inearlyJuly1991,
of which only one met the sizecriterion (TL < 105
cm) for successfulacclimatization tofreshwater.
We used 2m diametertanks.Uponarrival,most
fish hadlosttheirrightingresponse as aresult of the
stress of bothcatching andtransport.Heavy mor-
talityoccurred in thefirst 24hours forfish < 105 cm
TL (mean TL = 79 cm) afterdirecttransfer tofresh
water.Survivors were dividedinto two groups, one
remaining in freshwater and theother inbrackish
water(salinity = 5–10‰);however, all ofthesefish
eventually died, thelast onethreeweeks after
stocking and withouthaving Tedoverthattime. The
first fishtransferred tobrackishwaterdiedlater
than the others (<0.05,Mann-Whitney Utest). The
largestfish (TL = 130 cm, W = 10.8 kg) wasstill alive
in freshwater by the end ofAugust, but never fed
naturally. Weforce-fed it pelletsfrom one tothree
times a day.Afterhaving lostabout 25% of itsRearing oflarvaeWe recoverednearly 700embryos in1981, and
230 000 and 70 000 from the twofemalesstripped in- In1981,about tenlarvae werestill aliveafter
one month of rearing, afterwhichrearing was dis-
continued. In1985, allfree embryosdied at approxi-