Bul.Natl.SalmonResourcesCenter,No.8,26 2 Table1.PrevalenceofMyxoboluskisutchiinandsalmonfrom thecolumbiariverbasinanditsvicinities. Prevalence (%) No.offish infected No.offish examined Dateofcapture Locality River Stage Type Fish 43.5 27 62 Apr.1987 WoodyIslandtestfishery 64.7 11 17 Apr.1987 Corbettestfishery 43.4 36 83 Apr.1988 5.8 33 65 Apr.3,1989 11.4 5 44 Sep.14,1987 8.3 2 24 Sep.1988 18.3 11 6 Jun.16-18,1987 JonesBeach 29. 18 62 Jul.14-18,1988 1.7 1 59 Jun.21-24,1988 1.3 1 8 Jun.21-29,Jul.6,1989 37.1 23 62 May6& 7,1988 2.3 12 59 May8-1,1989 5 Feb.5,1991 RoundButeHatchery (DeschutesR.) 6 Mar.6,1991 Warm SpringsHatchery 9 Feb.27,1991 LeavenworthNationalFishHatchery (WenatcheeR.) 54 Mar.27,1991 DworshakNationalFishHatchery (ClearwaterR.) 91 Mar.13,1991 DworshakNationalFishHatchery (ClearwaterR.) 3 Apr.12,1991 DexterPonds (WilameteR.) 1 5 5 Mar.12,199 CowlitzSalmonHatchery (CowlitzRiver)? 4.5 1 22 Aug.5,199 HuppSpringsHatchery 4.5 15 37 Sep.23& 3,1996? 64.3 18 28 Apr.12,1996 SimpsonHatchery ChehalisR.(SatsopR.) 6. 3 5 Aug.5,199 Hatchery 83.9 26 Feb.1,1996 Hatchery 1 42 42 Apr.11,1996 Hatchery 3 Apr.1996 Hatchery 3 May4,1996 Hatchery 5. 3 6 Jun.7,1996 Hatchery 96.8 3 Jul.3,1996 Hatchery 1 3 3 Aug.1996 Hatchery 1 3 3 Sep.1996 Hatchery 1 Oct.15,1996 Hatchery 96.3 26 27 Nov.17,1996 Hatchery 1 53 53 Jan.1997 Hatchery 1 35 35 Mar.1997 Hatchery 1 28 28 Apr.1997 Hatchery
Urawaetal. Myxobolusksutchifrom salmonidbrains 3 Fig.1.Mapsindicatingsamplinglocations. Table2.SporecharactersofMyxoboluskisutchifrom thecentralnervetisuesofandsalmon. Host No.spores Location (Infectionsite) measured SL *1 SW *1 ST *1 PCL *1 PCW *1 NC *2 SW/SL Springsalmon ColumbiaRiver 6 1..5 9..4 6.8.3 5.3.4 3..2.9.4 (medulaoblongata) 1987 (9.-11.)* 3 (8.-9.8) (6.-7.2) (4.-6.) (2.5-3.8) (.8-1.) Falsalmon ColumbiaRiver 4 1.1.5 9.4.4 6.4.2 5.1.3 2.9.2 7.6.7.93.4 (medulaoblongata) 1988 (9.4-1.9)(8.6-1.1)(6.2-7.) (4.3-5.5) (2.3-3.3) (7-9) (.82-1.) salmon,199 3 1.4.5 8.9.5 6.5.4 5.2.4 2.9.2.85.5 (medulaoblongata) (9.5-11.)(8.-1.)(6.-7.2) (4.5-6.) (2.5-3.5) (.76-1.) Cohosalmon,199 3 8.9.6 7.2.5 5.2.3 4.8.4 2.7.4.82.7 (medulaoblongata) (8.-1.) (6.2-8.5) (4.9-6.) (4.-5.2) (2.-3.1) (.69-.98) Cohosalmon,1996 3 9.4.4 8..5 5.6.2 5.2.3 2.8.3 7.3.5.86.5 (medulaoblongata) (8.6-1.1) (7.2-9.) (5.2-6.2) (4.5-6.) (2.3-3.1) (6-8) (.76-.97) Cohosalmon,1996 3 9.7.3 7.8.3 5.6.3 5.1.3 2.7.2 7.2.5.81.4 (spinalcord) (9.4-1.1) (7.-8.6) (4.9-6.2) (4.7-5.5) (2.3-3.1) (6-8) (.72-.88) Cohosalmon *4 (spinalcord) - (7.5-8.5) (6.5-7.) (3.5-3.8) (3.8-5.5) *1SL,sporelength;SW,sporewidth;ST,sporethicknes;PCL,polarcapsulelength;PCW,polarcapsulewidth;inmm. *2NC,numberofcoilsperpolarfilament.*3Mean SD(range).*4Measurementsfrom sectionedmaterialbyyasutakeandwood(1957). halisriver(coastofwashingtontributary)during 199-96(Table1,Fig.1).Forthesurveyofseasonal occurenceofparasites,almonreared in the Minter Creek Hatchery were colected monthlyfrom April1996toApril1997.Thesewererearedinpond#17suppliedwithwater from.thewatertemperaturewasrecordeddailyduringthesurveyperiod.seawardmigrating(n=432)werecapturedat andjonesbeachinthelowercolum- biariverintheandearlysummerof1987-89.adultandsalmonwerecapturedinthelowercolumbiariver(n=295)andin (n=37).thefishsampleswerefrozen orfixedwith1% formalinandstoreduntilthetissueswereexaminedforparasites. Parasiteexamination Themedulaoblongataandspinalcordwereremovedfrom thefishsamplesandsmearedonslides. Thesmearedslideswereexaminedforthepresence ofm.kisutchisporeswithamicroscope(2 magnification).in addition,themonthly samples from thehatcherywereobservedfor
4 Bul.Natl.SalmonResourcesCenter,No.8,26 A B C Fig.2.PhotomicrographsofMyxoboluskisutchi.(A)Sporesinthespinalcordofsalmonfrom thehatchery. Scalebar=25mm.(B)Same.Scalebar=5mm.(C)Sporesinthemedulaoblongataofsalmonfrom thecolumbia River.Scalebar=5mm. parasitesinthelateralperipheralnerve.detected myxosporeanspores,viewedbyanormanskymicroscope,weredescribedaccordingtoguidelinesproposedbylom andarthur(1989).sporemeasurementsweremadefrom freshspecimens. Results Geographicaldistribution Parasite MyxosporeansporesofM.kisutchiweredetected amongtheneurofibrilsofthecentralnervetisues (medulaoblongataandspinalcord)ofand salmon,butnotinthelateralperipheral nerve.noapparenthostresponsewasobservedin theinfectionsites.trohozoites(n=6)wereiregular inshape,usualyelongated,2-64 16-29mm in size,andcontained5-23spores(fig.2a).thespore shapewasoviform oralmostroundinthefrontview (Fig.2B,C).Thesporesizewasslightlydiferent dependingonthehostfishes(table2):thespores from salmonweresignificantlylargerthan thosefrom salmon(p<.5).thewidthof shelmembranes was.6-.8 (mean.74)mm (n=1).twopyriform polarcapsuleslocatedatthe anteriorendoccupiedalmostthehalfofthespore length.polarfilamentscoiledinsideforming6-9 loops.thefilamentsextendedwith5% KOHmeasured52.5-87.5(mean66.6)mm (n=6).asmaltriangularintercapsularproceswaspresent. Myxoboluskisutchisporesweredetectedinsalmonandcapturedinthelower ColumbiaRiver(Table1).TheprevalenceofinfectioninmigratingseawardpasttheMcNary Dam,whichislocated467km upstream from the rivermouth,was2-37% inmay,droppedto1.3-1.7% injune,andincreasedagainto29% injuly. The prevalence of infection in adult salmoncapturedinthelowermainstream ofthecolumbiariverwas43-65% forruns,butlower (8-11%)forruns.Amongsixhatcheriesinthe ColumbiaRiverBasin,theparasitewasfoundonly insalmonfrom thecowlitzsalmonhatchery,where alsalmonexamined(n=5)were heavilyinfected.andsalmonrearedinthehatcheryandthe Simpson Hatchery were also infected with M. kisutchi. Seasonaloccurence InsalmonrearedattheMinter CreekHatchery,sporesofM.kisutchiwerenotpresentinAprilandMay,butappearedinthecentral nervetisuesinjune(fig.3).theprevalenceof sporeinfectionsincreasedto97% injuly,andremainedatalmost1% untilthenext,when fishreachedthetage. Discusion MyxoboluskisutchiwasfirstfoundbyYasukate
Urawaetal. Myxobolusksutchifrom salmonidbrains 5 Fig.3.SeasonalchangesinprevalenceofMyxoboluskisutchispores(closedcircles)inalmonrearedattheMinter CreekHatchery.Opencirclesindicatetheaveragerearingwatertemperatureineachmonth andwood(1957),buttheirdescriptionwasbased mainlyonhistologicalmaterials.thepresentdescriptionofm.kisutchiindicatesthatthefreshspore sizeislargerthanthatintheoriginaldescription, eventhoughthehostspecies(salmon)andlocation()werethesame(table2).this isapparentlyatributabletosporeshrinkageduring theprocesingofsectionedmaterials.itisnoteworthythatsporesfrom salmonwerelarger thansporesfrom salmon.hine(1979)alsoobservedvariationsinthesizeandshapeofmyxidium zealandicumsporesamonghostspecies. Severalothermyxosporeansarefoundinthe nervetisuesofsalmonids(schubergandschr`der 195;Pugachev and Khokhlov 1979;Gonzalez- LanzaandAlvarez-Pelitero1984;Hedricketal. 1991).Amongthesespecies,Myxoboluskisutchiis morphologicalyverysimilartom.neurobius.the firstrecordofm.neurobiuswasofspecimensfound inthespinalcordofbrowntrout(salmotruta)in Europe(SchubergandSchr`der195),andlaterM. neurobiuswasalsofoundinseveralsalmonidspeciesfrom thepacificcoastofasia(pugachevand Khokhlov1979;Awakuraetal.1982,1995;Urawa andawakura1994)andtheatlanticcoastofnorth America(Maloneyetal.1991).ThesporesofM. neurobiuswerefoundinthelateralperipheralnerve ofnorwegian brown troutand Japanese masu salmon(o.masou),aswelasinthebrainandspinalcord(urawaandegil,unpublisheddata).however,sporesofm.kisutchiwerenotpresentinthe peripheralnerve tisues of and salmon.thus,weproposethatm.kisutchiremains asanindependentspeciesatthepresenttime.future molecularandlifecyclestudiesarenecesaryfor thetaxonomyofmyxobolusspp.inthenervesof salmonids. Manypapersshow thatthelifecycleofmyxosporeansinvolvesanactinosporeanstageinaquatic oliogochaetesorpolychaetes.forexample,theoligochaetesstylodrilusheringianusandlumbriculus variegatusserveasthealternatehostofm.arcticus, whichinfectsthebrainandspinalcordofsalmonids (Kentetal.1993;UrawaandAwakura1994).We surveyed severalspeciesofoligochaetesin the duringtheearlyfebruaryof1996,but couldnotfindanyactinosporeans.ontheother hand,theseasonalsurveyindicatedthatsporesofm. kisutchiappearedinthecentralnervetisuesofinjune,severalmonthsafterhatching.the prevalenceimmediatelyincreasedtoalmost1% inthenextmonth,andthesporesremainedinthe nervetisuesthroughoutthehostlife.thesporeformationofm.arcticusoccurswithin3monthsafter infectionat1/c(urawaandawakura1994).thus salmonmaybecomeinfectedwithactino-
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