Toreplenishthedepletingpopulationsofsturgeon fishes especiallyPersiansturgeon, Acipenser persicus
in theCaspianSea,millionsofPersiansturgeon fingerlingsarefarmedthroughartificial propagationand
released intotheIranianriverestuariesannually.Fishosmoregulationisavitalphysiologicalprocessthat
can beaffectedduringtherelease.ManyIranianriverestuariesareundertheinfluence ofpesticides
originating fromfarmingactivitiesthatmayaffectosmoregulation.Inthisstudy,Persiansturgeon fingerlingswereexposedtosublethalconcentrations(0,0.18,0.54,0.9mgL1) ofdiazinonfor96h(short-
term trial)and12days(long-termtrial)infreshwater(FW)andthen fish wereexposedinbrackish
water(BW)for24h.After96hand12daysofexposureinFW,thelowerlevelsofplasmatriidothyronine
(T3), thyroxine(T4), Naþ, Cl, Kþ, gillNaþ/Kþ- ATPaseactivityandnumberofchloridecellswereob-
served inexposed fish (0.54and0.9mgL1 diazinon) comparedtocontrolgroupand0.18mgL1
diazinon treatment.Also,higherlevelsofplasmacortisol(except0.18mgL1 diazinon treatmentin
long-term trial)wereobservedindiazinonexposed fish comparedtocontrolgroup.However,gillNaþ/
Kþ-ATPaseactivityandthenumberofchloridecellswerehigherin fingerlingsexposedtodiazinon
compared thancontrol.When fish wereexposedinBWfor24h,thefollowingchangesoccurred:(a)in
short-term trial:increasesincortisolandCl levels (0.54mgL1 diazinon ),Naþ (0.9 mgL1 diazinon )
and gillNaþ/Kþ-ATPaseactivity(0.18mgL1 diazinon ).Incontrolgroup,cortisol,T4, Naþ, gillNaþ/Kþ-
ATPaseactivityandthenumberofchloridecellsincreasedsignificantly.(b)Inlong-termtrial:increases
in Kþ levelsin fish exposedto0.9mgL1 diazinon, Naþ in alldiazinonconcentrationsanddecreasesin
chloride cellsnumberin fish exposedto0.18mgL1 diazinon. Incontrolgroup,significant increases
wereobservedincortisol,T3, Naþ and chloridecellsnumber.Finally,gillshowedmanyhistopathological
damages duringexposureinFWandBW.Ourresultssuggestthatthecontaminationofriverestuaries
with diazinonmayaltertheosmoregulationabilityofreleasedPersiansturgeon fin