Supplemental observations on the morphology of Procamallanus (Spirocamallanus) hilarii (Nematoda: Camallanidae) parasitizing two species of Astyanax (Characiformes: Characidae) and ecological analyses

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Availableonlineatwww.sciencedirect.com

Revista

Mexicana

de

Biodiversidad

www.ib.unam.mx/revista/ RevistaMexicanadeBiodiversidad86(2015)590–596

Taxonomy

and

systematics

Supplemental

observations

on

the

morphology

of

Procamallanus

(Spirocamallanus)

hilarii

(Nematoda:

Camallanidae)

parasitizing

two

species

of

Astyanax

(Characiformes:

Characidae)

and

ecological

analyses

Observaciones

suplementarias

sobre

la

morfología

de

Procamallanus

(Spirocamallanus)

hilarii

(Nematoda:

Camallanidae)

parasitando

dos

especies

de

Astyanax

(Characiformes:

Characidae)

y

análisis

ecológico

Moisés

Gallas

∗

,

Cláudia

Calegaro-Marques,

Suzana

Bencke-Amato

LaboratóriodeHelmintologia,DepartamentodeZoologia,InstitutodeBiociências,UniversidadeFederaldoRioGrandedoSul,91501-970PortoAlegre, RioGrandedoSul,Brazil

Received8September2014;accepted13May2015 Availableonline1September2015

Abstract

Procamallanus(Spirocamallanus)hilariiparasitizesseveralfishspeciesbutonlyfewstudiesonmorphologyandecologyhavebeenpublished. InthisstudywedescribethemorphologyofP.(S.)hilariiparasitizingAstyanaxaff.fasciatusandAstyanaxjacuhiensis,andcompareecological parametersoftheirpopulations.SeventyA.aff.fasciatusand60A.jacuhiensisindividualswerecapturedinLakeGuaiba,RioGrandedoSulState, Brazil,betweenMarch2012andDecember2013.ThespecimensofP.(S.)hilariipresentedanovaloralopeningwith6cuticularelevationsand 2groupsofpapillae(oneinternalandoneexternal)intheanteriorregionofthebody.Maleshave8pairsofsessilecaudalpapillae(4pre-cloacal and4post-cloacal),spiculeswithdistalbifurcationandlackcaudalalae.TheprevalenceofP.(S.)hilariiwashigherinA.aff.fasciatus(69%) thaninA.jacuhiensis(18%),whereastherewasnodifferenceinmeanintensity(respectively,2and5)andmeanabundance(respectively,1.6and 0.9)ofinfectionbetweenthe2hostspecies.Wesuggestthattheconsumptionofcopepods,intermediatehostsofP.(S.)hilarii,mayexplainthis difference.

Keywords: Spiruridae;Taxonomy;Morphology;Characids;Neotropicalregion

Resumen

Procamallanus(Spirocamallanus)hilarii(P.(S.)hilarii)parasitavariasespeciesdepeces,perosonescasoslosestudiospublicadossobresu morfologíayecología.EnesteestudiodescribimoslamorfologíadeP.(S.)hilariiqueparasitanlasmojarrasAstyanaxaff.fasciatusyA.jacuhiensisy comparamosdiferentesparámetrosecológicosdesuspoblaciones.Entremarzode2012ydiciembrede2013,capturamos70individuosdeAstyanax (A.)aff.fasciatusy60deA.jacuhiensisenelLagoGuaiba,estadodeRioGrandedoSul,Brazil.LosejemplaresdeP.(S.)hilariipresentaron unaaberturaoraldeformaovalcon6elevacionescuticularesy2gruposdepapilas(unainternayotraexterna)enlaregiónanteriordelcuerpo. Losmachospresentaron8paresdepapilascaudalessésiles(4precloacay4poscloaca),espículasconbifurcacióndistalyausenciadealacaudal. LaprevalenciadeP.(S.)hilariifuemayorenA.aff.fasciatus(69%)queenA.jacuhiensis(18%).Sinembargo,noexistierondiferenciasenla intensidadpromedio(2y5respectivamente)ylaabundanciapromedio(1.6y0.9respectivamente)deinfecciónentrelas2especieshospederas. Sugerimosqueelconsumodecopépodos,hospederosintermediariosdeP.(S.)hilarii,podríaexplicarestadiferencia.

Palabrasclave: Spiruridae;Taxonomía;Morfología;Carácidos;Regiónneotropical

∗_{Corresponding}_author.

E-mailaddress:mgallas88@gmail.com(M.Gallas).

PeerReviewundertheresponsibilityofUniversidadNacionalAutónomadeMéxico.

http://dx.doi.org/10.1016/j.rmb.2015.07.005

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M.Gallasetal./RevistaMexicanadeBiodiversidad86(2015)590–596 591

Introduction

ProcamallanusBaylis,1923,agenusofnematodeparasites offreshwaterandmarinefishes(Moravec,Salgado-Maldonado, & Caspeta-Mandujano, 2000), was originally proposed to includeCucullanuslaeviconchusWedl,1862,aparasiteof fresh-watersiluriformfishesbasedonthemorphologyofthebuccal capsule(Baylis,1923).Olsen(1952)proposedSpirocamallanus

forgroupingthespeciesthathadspiralthickeningsinthe buc-calcapsule,whereasMoravecandSey(1988)considereditas asubgenusofProcamallanusbasedonthepresenceofbuccal capsulewithinnerspiralsinmalesandfemales.Gibbons(2010) hasrecentlyconsideredthelatterpropositionvalidandgrouped 6additionalsubgenerawithinProcamallanus.

Neotropical species of Procamallanus belong to the sub-genera Procamallanus Baylis, 1923, Spirocamallanus, and

DenticamallanusMoravecandThatcher,1997(Luque,Aguiar, Vieira,Gibson,&Santos,2011;Moravec,1998).Luqueetal. (2011)listedall22speciesofProcamallanussofarrecordedin Brazil.VazandPereira(1934)reportedProcamallanushilarii

VazandPereira,1994,parasitizingthesmallintestineof Salmi-nus hilarii Valenciennes, 1849 from the Santo Amaro Dam, São PauloState,Brazil. Later,this wasclassifiedin the sub-genusSpirocamallanusby presentingoral capsulewith inner spiralsinbothsexes(Moravec&Sey,1988).Thisspecieswas redescribedbyPintoandNoronha(1976)andRodrigues,Pinto, andNoronha(1991);however,inbothstudiestheauthorsused theoriginalfiguresofVazandPereira(1934),therebymissing many morphological details, such as cephalic characters and posteriorextremityofmales.

InBrazil,P.(S.)hilariiwasrecordedinthestatesofCeará inAstyanaxbimaculatus (Linnaeus, 1758) and Steindachner-ina elegans (Steindachner, 1874) (Pereira, Dias, & Azevedo, 1936),RiodeJaneiroinA.bimaculatusandAstyanax parahy-bae(Eigenmann,1908)(Abdallah,Azevedo,&Luque,2004), SãoPauloinA.bimaculatus(Kloss,1966;Kohn&Fernandes, 1987)andSalminushilariiValenciennes,1850(Vaz&Pereira, 1934), as well as unidentified minnows (Pinto & Noronha, 1976), Paraná in Astyanax fasciatus (Cuvier, 1819) (Kohn, Fernandes,Pipolo,&Godoy,1988;Pinto&Noronha,1976)and unidentifiedminnows(Pinto&Noronha,1976),andRioGrande do Sul in Acestrorhynchus microlepis (Schomburgk, 1841),

Astyanax jacuhiensis, Astyanaxaff. fasciatus,Hoplias lacer-daeMirandaRibeiro,1908,Hopliasmalabaricus,andRhamdia quelen(QuoyandGaimard,1824)(Kohn,Fernandes,Pipolo,& Godoy,1989).Thisnematodealsowasrecordedin Trichomyc-terus piurae (Eigenmann, 1922) in Peru (Freitas & Iba˜nez, 1970) and in Astyanax abramis, A. bimaculatus, A. fascia-tus,Hopliasmalabaricus,Leporinusobtusidens(Valenciennes, 1836),Oligosarcusjenynsii (Günther, 1864),Pimelodus albi-cans(Valenciennes,1840),andSalminusbrasiliensis(Cuvier, 1816)inArgentina(Ramalho,1997,2005).Luqueetal.(2011) also cited the characidOligosarcus macrolepisSteindachner, 1877as ahost ofthisspecies,butthe collectionsitewasnot reported.WhileLimaetal.(2003)andBuckup,Menezes,and Ghazzi(2007)reportthat O.macrolepisoccursinthe Jequit-inhonha river basin in Bahia and Minas Gerais, these states

were not surveyed by Luque et al. (2011).Their collections wererestrictedtothestatesofCeará,RiodeJaneiro,SãoPaulo, Paraná,andRioGrandedoSul.

Procamallanus(S.)hilariiwasrecordedinA.aff.fasciatus

andA.jacuhiensisbyKohnetal.(1989),butacomparisonof its ecological parametersbetweenthese hostspecies is miss-ing.The present studyaims tofulfill thisgapbyprovidinga detailed description ofthe morphologyof P.(S.) hilarii from LakeGuaiba,RioGrandedoSulState,Brazil,anddiscussing theirecologicalparametersinlightoftheirtrophicrelations.

Materialsandmethods

SeventyspecimensofA.aff.fasciatusand60ofA. jacuhien-sis were collected with seinenets between March 2012 and December 2013 from Lake Guaiba, in the municipalities of Guaiba (30◦0828S, 51◦1853W) and Barra do Ribeiro (30◦1711S,51◦1801W),StateofRioGrandedoSul,Brazil. Fisheswereindividuallypackedinplasticsacks,andtransported inicecoolerstotheLaboratóriodeHelmintologiaofthe Depar-tamentodeZoologia(DZ),UniversidadeFederaldoRioGrande doSul(UFRGS)fornecropsy.Hostsweredeterminedaccording toLucena,Castro, andBertaco(2013).Nematodes were col-lected,fixed,andpreservedfollowingAmatoandAmato(2010). TheseweretemporarilymountedandclearedinAmann’s lac-tophenol(Humason,1979).Enfacepreparationsweremounted in glycerin jelly according to Anderson (1958) to visualize cephaliccharacters.Specimenswerepreparedforscanning elec-tronmicroscopy(SEM)throughdehydrationinethanol(70◦to 100◦GL) andtheethanol wasgradually replacedbyacetone (10–100%)tocriticalpointdried.Then,theyweremountedon stubs,coatedwithcarbonandgold,andexaminedinaJEOLJSM 6060atCentrodeMicroscopiaEletrônica(CME)atUFRGS.

Measurementsareshowninmicrometers(␮m)unless other-wisestated.Theparametersreportedaretherangefollowedby mean±standarddeviation,andsample sizeisbetween paren-theses. Photomicrographs were taken with a Zeiss Axiolab microscopewithphasecontrast.Linedrawingsweremadewith adrawingtubemountedonaNikonE-200microscope,scanned andpreparedusingCorelDrawX4®andAdobe’sPhotoshop® CS2. Ecological parametersfollow Bush, Lafferty, Lotz, and Shostak (1997). Voucherhelminth specimens weredeposited in the ‘Colec¸ão Helmintológica do Instituto Oswaldo Cruz’ (CHIOC),RiodeJaneiro,RJ,Brazil.Voucherhostspecimens weredepositedinthe‘Colec¸ãoIctiológica’,DZ/UFRGS.The

Z-testwas usedtocompare prevalencedatabetweenthe host species, whereas median intensity and median abundance of infectionwerecomparedbytheStudentttest(Zar,2010).

Description

Procamallanus(Spirocamallanus)hilariiVazandPereira, 1934(Figs.1–18)

Diagnosis (based on 15 males and 15 females mounted in lactophenol, 2 en face, and 5 males prepared for scanning electron microscopy). Spiruroidea, Camallanidae.

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Figures1–6.IncompletediagramsofProcamallanus(Spirocamallanus)hilarii.(1),Anteriorextremityofmales.Scalebar=150␮m;(2),enfaceview.Scale bar=50␮m;(3),posteriorextremityofmales.Scalebar=50␮m;(4),detailoftheventralviewofthespicules.Scalebar=50␮m;(5),vulvarregionoffemales. Scalebar=100␮m;(6),posteriorextremityofayoungfemale.Scalebar=150␮m.

Reddish nematodes in life, with transverse cuticular stri-ations. Oval mouth opening surrounded by 6 elevations (1 ventral, 1 dorsal, and 4 lateral), and 8 papillae dis-tributed in2circles (4 internalsmallerand4 externallarger) (Figs.2,8,9and16).Yellowishbrownbuccalcapsule, sclero-tized,with13–16internalspirals,continuous,someincomplete (Figs.1,7, 15and16).Basal ringsclerotizedbetweenbuccal capsule and muscularesophagus (Figs. 1 and 7). Esophagus dividedintoashortermuscularandalongerglandularportion (Figs.1and7).Nerveringanteriortodeiridsandexcretorypore (Figs. 1, 7, 15and 17).Males (N=15). Body 6.34–9.07mm (7.58±0.89mm;N=15)long,0.16–0.22mm(0.18±0.02mm;

N=15) wide. Buccal capsule 45.00–70.00 (53.17±5.71;

N=15) long, 52.50–65.00 (56.67±3.74; N=15) wide, with 13–16 internal spirals. Basal ring 7.50–12.50 (9.67±1.30;

N=15) long, 20.00–40.00(32.50±4.82; N=15) wide. Mus-cularesophagus340.00–460.00(390.00±34.11;N=15)long, 50–70 (59.67±5.50; N=15) and 100–130 (113.33±10.47;

N=15) widein the anterior andposterior ends, respectively; glandular esophagus 1.04–1.77mm (1.40±0.20mm; N=15) long, 0.09–0.14mm (0.11±0.01mm; N=15) wide. Esoph-agus representing 24% of total body length (TBL), and muscular portioncorresponding to28%of the glandular por-tion.Nervering162.50–222.50(195.83±16.63;N=15)from anterior extremity. Deirids 185.00–282.50 (235.00±24.68;

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M.Gallasetal./RevistaMexicanadeBiodiversidad86(2015)590–596 593

Figures7–11.PhotomicrographiesofmalesofProcamallanus(Spirocamallanus)hilarii.(7),Anteriorextremityinphasecontrast.Scalebar=100␮m;(8),enface

viewshowingthe6cuticularelevations(whitearrowheads).Scalebar=50␮m;(9),enfaceviewshowingthe4outerpapillae(whitearrowheads),amphids(black arrowheads)andtheendofthebuccalcapsule(asterisk).Scalebar=50␮m;(10),posteriorextremityshowingthespicules(blackarrowheads).Scalebar=50␮m; (11),detailoftheventralviewofthespiculesshowingthedistalbifurcation(whitearrowheads).Scalebar=50␮m.

(279.17±36.37;N=15)fromanteriorextremity.Posteriorend ofthebodywith8pairsof papillae:4pre-and4post-cloacal (Figs. 3, 10 and 18). Similar spicules, bifurcated distal end, withlengthof52.50–77.50(64.83±5.94;N=15)and62.5–87.5

(72.83±6.54; N=15) (Figs. 3, 4, 10 and 11). Gubernacu-lum absent. Cloaca 120.00–200.00 (162.83±25.03; n=15) fromtheposteriorextremity,pointedtail(Figs.3,10and18). Females (N=15). Body 12.92–18.78mm (15.69±1.93mm;

Figures12–14.Photomicrographies offemales ofProcamallanus(Spirocamallanus) hilarii.(12),Vulvar region withlarvae L1(whitearrowheads). Scale bar=250␮m;(13),posteriorextremityofagravidfemaleshowinglarvaeL1(whitearrowheads).Scalebar=100␮m;(14),larvaestainedwithrosebengal. Scalebar=100␮m.

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Figures15–18.ScanningelectronmicroscopyofProcamallanus(Spirocamallanus)hilarii.(15),Anteriorextremitywithdeirid(blackarrowhead)andexcretory pore(whitearrowhead).Scalebar=50␮m;(16),detailoftheanteriorextremityshowingcuticularelevations(asterisks),innerpapillae(blackarrowheads),outer papillae(whitearrowheads)andamphids(blackarrows).Scalebar=10␮m;(17),detailofthedeirid.Scalebar=10␮m;(18),posteriorextremityofamaleshowing thephasmids(whiteheadarrows).Scalebar=20␮m.

N=15) long, 0.22–0.44mm (0.34±0.06mm; N=15) wide. Buccal capsule 55.00–65.00 (60.00±3.13; N=15) long, 60.00–72.50 (66.67±3.62; N=15) wide, with 13–16 inter-nalspirals.Basalring7.50–12.50(10.67±1.48;N=15)long, 35.00–45.00 (39.67±2.81; N=15) wide. Muscular esopha-gus370.00–520.00(434.00±36.41;N=15)long,60.00–80.00 (69.33±4.58; n=15) and 120.00–150.00 (128.67±9.9;

n=15) wide in the anterior and posterior ends, respec-tively; glandular esophagus 1.15–2.22mm (1.77±0.26mm;

N=15) long, 0.12–0.17mm (0.14±0.01mm; N=15) wide. Esophagus representing 11% of TBL, and muscular por-tion corresponding to 25% of the glandular portion. Nerve ring 182.50–232.50 (207.17±14.48; N=15) from anterior extremity. Deirids 250.00–350.00 (285.77±34.86; N=13) from anterior extremity. Excretory pore 280.00–410.00 (341.04±47.07; N=12) from anterior extremity. Vulva post-equatorial, 5.48–7.94mm (6.82±0.76mm; N=15) from posterior extremity (Figs. 5 and 12). Eggs 7.50–10.00 (9.00±1.29) long and 5.00 to 10.00 (7.50±1.67) wide (N=10),withfirstlarvalstage390.00–529.50(514.97±60.38;

N=15) long and 25.00–32.50 (27.00±3.02; N=15) wide (Figs. 12, 13 and 14). Anus 80.00–140.00 (111.33±16.42;

N=15)fromposteriorextremity,pointedtail(Figs.6and13).

Taxonomicsummary

Synonyms: Procamallanus cearensis Pereira, Dias and Azevedo, 1936; SpirocamallanusincarocaiFreitas&Iba˜nez, 1970.

Hosts:A.aff.fasciatusandA.jacuhiensis.

Hostspecimensdeposited.A.aff.fasciatus:UFRGS19121 (male); UFRGS 19122 (female)and A. jacuhiensis: UFRGS 19123(male);UFRGS19124(female).

Localities:LakeGuaíba,MunicipalitiesofGuaíbaandBarra doRibeiro,StateofRioGrandedoSul,Brazil.

Siteofinfection:stomachandintestine.

Voucherspecimensdeposited:CHIOCn◦35948.

Ecological parameters: the prevalence of P. (S.) hilarii

in A. aff. fasciatus (69%) was higher than in A. jacuhiensis

(18%) (Z=5.7355, ptwo-tailed<0.0001; Table 1). However,

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M.Gallasetal./RevistaMexicanadeBiodiversidad86(2015)590–596 595 Table1

EcologicalparametersofProcamallanus(Spirocamallanus)hilariipopulationsandfeedinghabitsofhostspecies. Host Nhost Diet Prevalence(%) Meanintensity

(helminths/host) Mean abundance (helminths/host)

Reference

Astyanaxabramis 228 Juveniles:vegetalmatterand insects.Adults:

microcrustaceans, crustaceansandinsectsa

52 3 – Ramalho(2005)

Astyanax bimaculatus

124 Vegetalmatter,insectsand otheranimals(spiders andfishrests)b

45 3 – Ramalho(2005)

37 40 2 – Ramalho(2005)

23 4 – – KohnandFernandes(1987)

40 3 1 <0.1 Abdallahetal.(2004)

Astyanaxfasciatus 412 Vegetalmatter,insectsand somemicrocrustaceansc

56 2 – Ramalho(2005)

16 6 1 0.1 Kohnetal.(1988)

Astyanaxaff.

fasciatus

70 Vegetalmatter,insectsand somemicrocrustaceansc

69 2 1.6 Presentstudy

8 25 1 0.3 Kohnetal.(1989)

Astyanaxjacuhiensis 17 Vegetalmatterandinsectsc ₆₅ ₂ _1.2 _Kohn_et_al.₍₁₉₈₉₎

60 18 5 0.9 Presentstudy

Astyanaxparahybae 40 * ₅ ₁ _0.1 _Abdallah_et_al.₍₂₀₀₄₎

Acestrorhamphus macrolepis

11 * 45 3 1.4 Kohnetal.(1989)

Hopliaslacerdae 3 Adults:fishd 33 1 0.3 Kohnetal.(1989)

Hopliasmalabaricus 6 Juveniles:insectsand crustaceans.Adults:fish andshrimpe

17 2 0.2 Kohnetal.(1989)

Rhamdiaquelen 8 Fish,molluscs,crustaceans andinsectse

12 2 0.1 Kohnetal.(1989)

a _Barros₍₂₀₀₄₎_.

b _Andrian,_Silva,_and_Peretti₍₂₀₀₁₎_. c _Vilella_et_al.₍₂₀₀₂₎_.

d _Alvim_and_Peret₍₂₀₀₄₎_. e _Malabarba_et_al.₍₂₀₁₃₎_. * _Unknown_data.

jacuhiensis=5 helminths/host; t=−0.87, df=10,p=0.4)and themeanabundance(A.aff.fasciatus=1.6helminths/hostvs. A.jacuhiensis=0.9 helminths/host;t=1.24, df=70,p=0.22) ofinfectionweresimilarbetweenspecies(Table1).

Remarks

Thenematodesfoundinthestomachandintheanteriorand middle portions of the small intestine of A. aff. fasciatus

andA. jacuhiensis were identified as P. (S.) hilarii based on the taxonomickeys proposedby Rodrigues etal.(1991) and Moravec(1998)bypresentinganoralcapsulewithinnerspirals inbothsexesandaglandularesophagusatleast3timeslonger thanthemuscularesophagus.

SpeciesofProcamallanushave6elevationsdistributedover theanteriorregionofthebuccalcapsule,8papillaearrangedin 2circles,andapairoflateralamphids(Moravec,1998).Unlike theroundoralopeningreportedforP.(S.)hilariibyMoravec (1998),thespecimensexaminedpresentedanovaloralopening. Ramalho(1997)citedthepresenceof3pairsofsmallcephalic papillae,1lateraland2median.Infact,thesepapillaearethe cuticularelevationsdescribedbyMoravec(1998)andobserved inthepresentstudy(Figs.2,8,9and16).

Morphological differences also were found in the pos-terior end of males. In species considered synonymous of

P.(S.)hilarii,P.cearensisandS.incarocai,Pereiraetal.(1936)

andFreitasandIbañez(1970)mentionedthepresenceof thin caudalalae,whereasRodriguesetal.(1991)andMoravec(1998) notedtheabsenceofcaudalalaeasreportedinthepresentstudy (Figs. 3, 10and18).FreitasandIbañez(1970)andRamalho (1997)described8pairsofpedunculatepapillae,unlikethe ses-silepapillaereportedhere(Figs.3, 10and18)andinPereira et al. (1936), Rodrigues et al. (1991), and Moravec (1998). Additionally, although the spicules of the specimens exam-ined in the present study are similar to those described by Pereira etal.(1936),theseauthorsdidnotreportthe bifurca-tionof itsdistalend.In general,thedimensionsofcharacters were similar to those reported in the literature (Freitas & Ibañez, 1970; Pereira et al., 1936; Pinto & Noronha, 1976; Ramalho,1997;Rodriguesetal.,1991;Vaz&Pereira,1934). Maleandfemalebodysizewasanexception.Thetotallength of malesandfemalesreportedinthisstudywas higher.Only FreitasandIbañez(1970)reportedlargerfemales.Theseauthors alsoreportedthatthevulvaiscloser(2.4mm)totheposterior endof the worm.Morphological differencesmayresult from intraspecific variations in length, for example, or from diffi-cultiesinvisualizingstructures,aswasthecaseforthecaudal papillaeandcaudalalae.However,theMEVimagesclarifythese discrepancies.

Ecological parameters of P. (S.) hilarii populations vary amonghostspeciesandstudy(Table1).Forinstance,prevalence rangesfrom3%inA.bimaculatusto69%inA.aff.fasciatus.

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Thesedifferencessuggestthatthedefinitivehostsexploita vari-ablediet indifferent environments.In thecaseof thepresent study, thedifferences inprevalence of P.(S.) hilarii between the2characidhostslikelyreflectthedifferencesintheir feed-inghabits.SincethelifecycleofProcamallanusspp.includes copepodsasintermediatehosts(Anderson,2000),itispossible tosuggestthatthesesmallcrustaceansaremoreheavilypreyed uponbyA.aff.fasciatusthanbyA.jacuhiensis.Itisalso inter-estingthattheintensityofinfectionshowedtheoppositepattern, beinghigherinA.jacuhiensis,aspecieswithamore herbivo-rousdiet (Villela,Becker,&Hartz, 2002).Together,the data onprevalence andintensity of infectionmaysuggest thatthe fewerA.jacuhiensisindividualsthatfeedoncopepodsdothat atahigherfrequencythanmostA.aff.fasciatus.In addition, variationsinenvironmentalcharacteristicscanberelatedtothe availabilityintheenvironmentofinfectedcopepods.

Acknowledgements

WethankDra.AnaP.S.Dufechforfieldassistance,Dr.Philip J.SchollforreviewingtheEnglish,andCentrodeMicroscopia Eletrônica (UFRGS) for SEM preparations. MG also thanks theBrazilianNationalResearchCouncil(CNPq) forfinancial support(process#131068/2012-1)andCCMthanksthe Brazil-ian Higher Education Authority (CAPES) and the Research FoundationoftheStateofRioGrandedoSul(FAPERGS)for post-doctoralfellowships(PNPD/CAPES2010).

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