(Zebrasoma flavescens) in the marine ornamental aquarium fish trade

19 Pages·2015·17.25 MB·English

ff
The e ects of venting and decompression
on Yellow Tang (Zebrasoma flavescens) in
the marine ornamental aquarium fish
trade
EmilyS.Munday1,BrianN.Tissot2,JerryR.Heidel3 and
TimMiller-Morgan3,4
1SchooloftheEnvironment,WashingtonStateUniversityVancouver,Vancouver,WA,USA
2MarineLaboratory,HumboldtStateUniversity,Trinidad,CA,USA
3VeterinaryDiagnosticLaboratory,CollegeofVeterinaryMedicine,OregonStateUniversity,
Corvallis,OR,USA
4AquaticAnimalHealthProgram,OregonSeaGrant/CollegeofVeterinaryMedicine,Oregon
StateUniversity—HatfieldMarineScienceCenter,Newport,OR,USA
ABSTRACT
Eachyear,over45countriesexport30millionfishfromcoralreefsaspartofthe
globalmarineornamentalaquariumtrade.Thiscatchvolumeispartlyinfluenced
bycollectionmethodsthatcausemortality.Barotraumainfishresultingfromforced
ascentfromdepthcancontributetopost-collectionmortality.However,imple-
mentingdecompressionstopsduringascentcanpreventbarotrauma.Conversely,
venting(puncturingtheswimbladdertoreleaseexpandedinternalgas)following
ascent can mitigate some signs of barotrauma like positive buoyancy. Here, we
evaluatehowdecompressionandventingaffectstressandmortalityintheYellow
Tang(Zebrasomaflavescens).Weexaminedtheeffectsofthreeascenttreatments,
eachwithdecompressionstopsofvaryingfrequencyandduration,coupledwith
orwithoutventing,onsublethaleffectsandmortalityusinghistologyandserum
cortisolmeasurements.Infishsubjectedtoascentwithoutdecompressionstopsor
venting,ameanpost-collectionmortalityof6.2%occurredwithin24hofcapture.
Submitted4November2014 Commoncollectionmethodsinthefishery,ascentwithoutdecompressionstops
Accepted 20January2015
coupledwithventing,oronelongdecompressionstopcoupledwithventing,resulted
Published 17February2015
innomortality.Histopathologicexaminationofheart,liver,headkidney,andswim
Correspondingauthor
bladdertissuesinfish0dand21dpost-collectionrevealednosignificantbarotrauma-
EmilyS.Munday,
[email protected] orventing-relatedlesionsinanytreatmentgroup.Ascentwithoutdecompression
stopsresultedinsignificantlyhigherserumcortisolthanascentwithmanystops,
Academiceditor
RobertToonen whileventingalonedidnotaffectcortisol.Futureworkshouldexaminelinksinthe
supplychainfollowingcollectiontodetermineiffurtherhandlingandtransport
AdditionalInformationand
Declarationscanbefoundon stressorsaffectsurvivorshipandsublethaleffects.
page15
DOI10.7717/peerj.756
Subjects Aquaculture,FisheriesandFishScience,ConservationBiology,EnvironmentalSciences,
Copyright MarineBiology,SciencePolicy
2015 Mundayetal. Keywords Aquariumfish,Venting,Fishphysiology,Fishbarotrauma,Fishcortisol,
Aquariumtrade
Distributedunder
CreativeCommonsCC-BY4.0
OPENACCESS
HowtocitethisarticleMundayetal.(2015),TheeffectsofventinganddecompressiononYellowTang(Zebrasomaflavescens)inthe
marineornamentalaquariumfishtrade.PeerJ3:e756;DOI10.7717/peerj.756
INTRODUCTION
Eachyear,over45countriesremoveandexport14–30millionfishfromcoralreefsas
partofthemarineornamentalaquariumtrade(Bruckner,2005;Wood,2001).Although
∼90%offreshwateraquariumfisharesuccessfullycultivatedinaquaculturefacilities,most
tropicalmarineaquariumfisharewild-caught(Wood,2001).Collectinglivefishforthe
aquariumtradeinvolvesremovingreeffishfromSCUBAdivingdepths(∼10–35m)tothe
surface.Collectionisfollowedbytransportingfishfromthecollectionsitetoanexport
facilitywheretheyareheldfor1–7dayspriortoshipment.Thefisharethenpackagedin
plasticbagswithenoughwatertoturnaroundinand100%oxygen,placedinboxes,and
shippedtoanimportfacilitywheretheymaybeheldforseveraldays.Thefishthenare
transportedtoaretailstoreand,finally,toahobbyistaquarium.Mortalitymayoccurat
anypointinthissupplychain,impactingeachparticipantintheindustry,andnegatively
affectingcoralreefsthroughincreasedcollectionpressuretoreplacelosses(Stevenson,
Tissot&Dierking,2011;Tissotetal.,2010).
Aquariumfisheriesthatusedestructivefishingpractices(e.g.cyanideisusedtostun
ornamentalfishforeaseofcapture)havehighfishmortality,andthispracticeisstill
widespread(Hall&Bellwood,1995;Hanawaetal.,1998;Rubecetal.,2001;Rubec&Cruz,
2005;Belletal.,2009).WhilefishersinHawaiidonotusecyanidetocollectfish(Walsh
etal.,2004),andimmediatemortalityislow(<1%)(Stevenson,Tissot&Dierking,2011),
levelsofdelayedmortalityareunknown.Becausefishmoverapidlythroughthesupply
chain,itispossiblethataquariumfishersareunawareofcollectionmethodsthatresultin
mortalityfurtheralongthesupplychain.Economically,delayedmortalityshiftstheburden
offishdeathandmonetarylossfromthecollectortothosefurtheralongthesupplychain
(e.g.,theimporter,orhobbyist)whilealsoincreasingthedemandforfishandexacerbating
pressureoncoralreefecosystems.Identifyingmethodsthatcausedelayedmortalitywould
reducetheoverallmortalityofaquariumfishintheaquariumtrade,andthusthenumber
offishremovedfromthereeftocompensatefortheselosses.
Inordertoidentifyindustrymethodsthatcausedelayedmortalityinaquariumfish,itis
necessarytoexamineeachlinkintheaquariumfishtradesupplychainbothindependently
andinsuccession.Inthisstudy,weexaminethefirststepinthesupplychain:removing
fishfromdepth(15–18m)tothesurface.Mortalitycausedbyremovinglivefishfromcoral
reefdepthstothesurfaceisanimportantandcontroversialissueaffectingtheaquarium
fishery;toourknowledge,oursisthefirststudytoexaminethisproblem.
Toensurethatfishsurvivethetransitionfromdepthtothesurface,aquariumfishers
must either prevent or mitigate barotrauma. Fish experience barotrauma when they
are brought to the surface. As water pressure decreases, the volume of swim bladder
gasincreases.ThisphenomenonisaresultofBoyle’sLaw,inwhichdecreasingpressure
causesanexponentialincreaseingasvolume.Barotraumasignsinfishmanifestboth
externallyandinternally,andinclude:positivebuoyancycausedbyoverexpansionofthe
swimbladder;bulgingoftheeyes,orexophthalmia;andprotrusionoftheintestinefrom
thecloaca.Whilebarotraumahasnotbeenstudiedinshallow-dwelling(15–18m)reeffish
caughtfortheaquariumtrade,thereisampleresearchontheeffectsofdepthchangeson
Mundayetal.(2015),PeerJ,DOI10.7717/peerj.756 2/19
Table1 Externalandinternalsignsofbarotraumaobservedinfoodfishes.
External Internal
Gotshall,1964 Esophagealeversion
Bruesewitz,Coble&Copes,1993 Esophagealeversion
Keniryetal.,1996 Esophagealeversion,positivebuoyancy
StJohn&Seyers,2005 Esophagealeversion,exophthalmia
Parkeretal.,2006 Esophagealeversion
Hannah&Matteson,2007 Esophagealeversion
Hannah,Parker&Matteson,2008 Esophagealeversion,exophthalmia
Jarvis&Lowe,2008 Subcutaneousgasbubbles,esophageal Arterialembolism,hemorrhage,organtorsion
eversion,exophthalmia
Nichol&Chilton,2006 Rupturedswimbladder
Rogersetal.,2008 Exophthalmia Damagetoanddisplacementoforganssurrounding
swimbladder
Pribyletal.,2009 Esophagealeversion,exophthalmia Emphysemaofheartventricle
Wilde,2009 Esophagealeversion
Brownetal.,2010 Cloacalprolapse,exophthalmia,esophageal
eversion
Pribyletal.,2011 Esophagealeversion Emphysemaofheartventricleandepithelialsurfaces,
gasemboliinretemirabileandheadkidney
deeperdwelling(20–152m)fishcaughtcommerciallyandrecreationallyforconsumption
(Table1).
Priorresearchhasdemonstratedthatfishcontinuetoexhibitsublethalinjuries(not
having caused death) for extended periods. Rupture of the outer layer of the swim
bladder (tunica externa) persisted for at least one month after collection in rockfish
(genusSebastes)(Pribyl,2010).Thisindicatesthatsublethalsignsofbarotraumapersist
longaftertheinitialtraumaoccurs.Knowingthis,wepredictthatfishcollectedforthe
liveornamentalaquariumtradealsosuffersublethalinjuriesthatcouldresultindelayed
mortality.
Becausebarotraumacanbepotentiallyfataltobothshallower-dwellingaquariumfish
anddeeper-dwellingfoodfishalike,fishersimplementmethodsthateitherpreventor
mitigateit.Ventingisamethodthatmitigatesbarotraumaandinvolvespuncturinga
fishswimbladderwithahypodermicneedletoallowgasestoescapetheswimbladder,
relieving positive buoyancy. Decompression, in contrast, is a method that prevents
barotrauma.Decompressioninvolvestransportingfishfromdepthtothesurfaceovera
longerperiodoftime,whichallowsexpandinggasestoberemovedfromtheswimbladder,
resultinginafishthatisnotsubjectedtobarotraumaatall.Fishersimplementoneorsome
combinationofbothofthesemethodsinordertohelpfishsurvivethepressuretransition.
Whiletheuseofventinganddecompressiononaquariumfishhasbeendocumented
(Randall,1987;Pyle,1993;LeGore,Hardin&Ter-Ghazaryan,2005),oursisthefirststudyto
evaluatetheefficacyofeachoftheseproceduresinpreventingmortality.
Mundayetal.(2015),PeerJ,DOI10.7717/peerj.756 3/19
Indeeper-dwellingfishes,decompressiontakesalongtime—uptoseveraldays(Parker
etal.,2006;Pribyl,2010).Inordertopreventbarotrauma,onemustallowadequatetime
forfishtonaturallyremovegasfromtheexpandingswimbladder.Likewise,inHawaii
wherefisherscollectshallow-dwellingreeffish,ascentwithmultipledecompressionstops
canbetime-consuming(∼2h).Providingfishtimetonaturallydecompressandremove
swimbladdergasespreventsfishersfrommovingfromonereefsitetoanotherbecausefish
collectioncontainersmustbeattachedtothesurfacevessel.Fisherswouldratherremove
fishfromdepthquicklyinordertomovetoanotherreefsite,returntodepth,andcollect
morefish.However,bringingfishuptothesurfacequicklywithoutdecompressionstops
resultsinbarotrauma.Tomitigatethisbarotrauma,fishersuseventing.
Researchondeeper-dwellingfoodfishesdisagreethatventingreducesfishmortality.
Thisislargelyanartifactofthedifferencesinspeciesanddepthsthestudiesexamine
(Gotshall,1964;Keniryetal.,1996;Shasteen&Sheehan,1997;Collinsetal.,1999;Kerr,2001;
Nguyenetal.,2009;Wilde,2009)aswellasdifferencesinthelengthoftimefishareobserved
incaptivity.Wepredictthatlong-termholdingwillallowustodefinitivelyconcludehow
collectionmethodsaffectfishhealth.
Aspreviouslystated,fishersoftenusesomecombinationofdecompressionandventing.
Forexample,itiscommonforaquariumfisherstoperformoneorseveraldecompression
stops,pausinginthewatercolumnatintermediatedepthsbeforeremovaltothesurface
(LeGore,Hardin&Ter-Ghazaryan,2005;Stevenson,Tissot&Dierking,2011).InHawaii,
fisherstypicallyventthefishfollowingthispractice.Whilethesemethodsofbarotrauma
preventionandmitigationlikelypositivelyaffectfishhealthandmortality,thesepractices
are controversial among the animal rights community. Such groups in Hawaii have
repeatedly proposed legislation that would ban the harvest of marine species for the
aquariumtradebasedonanimalcrueltyclaims(seeLauer,2011;Talbot,2012;Wintner,
2010;Wintner,2011).Groupsopposedtoventingclaimthatitinflictsstressandmortality
onfish,whilecollectorsmaintainthatventingisnecessaryforfishsurvival.Peoplewho
opposeventinghavesuggestedthatdecompressionbeusedinstead.Whilewemaynot
solve the values conflicts driving in this controversy, we do hope to inform pending
managementdecisionsrelatedtoaquariumfishcollectioninHawaii.
Inourstudy,weseekto:(1)Determineshort-andlong-termmortalityofreeffish
caughtfortheaquariumtradesubjectedtothebarotraumapreventionand/ormitigation
practicesofdecompressionandventing,respectively;(2)Examinesublethaleffectsof
collectionthatcouldresultindelayedmortality.
METHODS
Experimental design
ThisstudywasconductedonthewestcoastoftheislandofHawaiiinJune–July2011.
TheYellowTang(Z.flavescens)wasselectedasthestudyanimalbecauseitisthemost
commonlytargetedaquariumfishspeciesinHawaii,consistentlycomposingnearly80%of
thetotalcatchofaquariumfishthere(Cesaretal.,2002;Tissot&Hallacher,2003;Walshet
al.,2004;Williamsetal.,2009).Inaddition,Acanthuridae,thefamilyencompassingYellow
Mundayetal.(2015),PeerJ,DOI10.7717/peerj.756 4/19
Tangandothersurgeonfishes,isoneofthemostcommonfamiliestargetedgloballyinthe
liveaquariumtrade(Rhyneetal.,2012).Therefore,understandinghowcollectionpractices
affectYellowTanghealthandsurvivalisespeciallyrelevanttothemarineaquariumfishery.
ToexaminetheeffectsofcollectionpracticesonmortalityofYellowTang,weused
a fully crossed factorial experimental design. Three decompression treatments (no
decompressionstops,onedecompressionstop,manydecompressionstops)werecoupled
withventing(yes,no)inallpossiblecombinations(k=6treatments)(Fig.1).Eachofthe
sixtreatmentswasreplicatedthreetimes,withn=20fishineachreplicateforatotalof360
individualfish.
YellowTangweresubjectedtocollectionmethodstypicalofthefishery,aselucidated
throughinterviewswithactiveaquariumfishers.Fishwerecollectedbetween15–18m
depth,reflectingtherangefrequentedbyHawaiiancollectors(Stevenson,Tissot&Dierking,
2011).Inordertoaccuratelyreflectmethodsusedbyaquariumfishers,anaquariumfisher
withover15yearsofexperiencecollectedthefish.Oneaquariumfisherperformedthe
experimentinordertomaintainconsistentmethodsthroughouttheexperiment.Working
withseveralfisherswouldbeideal,butthiswasnotlogisticallyorfinanciallyfeasible.
FishcollectionoccurredonSCUBAusingabarriernet,asdescribedbyStevenson,Tissot
&Dierking(2011).Followingcapture,fishweretransferredtocontainersassignedtoan
ascenttreatment.Followingascenttothesurfacevessel,halfofthefishwereventedandhalf
werenot.
Threeascenttreatmentswereused:(1)ascentwithoutdecompressionstops,(2)ascent
withonedecompressionstop,and(3)ascentwithmultipledecompressionstops.Therate
ofascentbetweendecompressionstopswas0.25m/sforalltreatments,therecommended
SCUBAascentrateandtheratefishersascendwhiletransportingfishfromdepthtothe
surface.Fishsubjectedtoascentwithoutdecompressionwerebroughtdirectlytothe
surfacefromdepth.Fishsubjectedtoascentwithonedecompressionstopwerebrought
uptohalfthemaximumdepthfora45mindecompressionstop,andthenbroughttothe
surface.Fishsubjectedtomultipledecompressionstopswerebroughtup3mevery15min.
At10m(2atm),thesefishwerebroughtup1.5mevery15minbecausethevolumetric
changeresultingfromthedecreaseinpressureisespeciallygreatthelastfewmetersof
ascent.Asistypicalinthefishery,ventingwasperformedbythefisheronthefishing
vesselusinga20Ghypodermicneedle,whichwasreplacedafterapproximately50fish.
Eachfishwasheldoutofwaterforlessthan3sbythefisherwhiletheneedlewasinserted
throughthebodywalltowardtheswimbladder,caudaltothepectoralfinandventralof
thelateralline.Followingcollection,fishweretransportedinthevessel’slivewelluntilthey
reachedtheholdingfacility.Duringcollectionandtransitfromcollectionsitetoport,fresh
seawaterwascontinuouslycirculatedthroughthelivewell.
Initialhistologicdiagnosticswereperformedonfish(n=5ineachreplicategroup)
immediatelyuponarrivalattheholdingfacilitytodeterminebaselinehealthaswellas
toassesstheimmediateeffectsofventinganddecompression.Allfishthatdiedwere
examinedhistologicallytoidentifylesionsthatcouldhavecontributedtodeath.Afinal
histologicdiagnosticexaminationwasalsoperformedonsurvivingfishattheconclusion
Mundayetal.(2015),PeerJ,DOI10.7717/peerj.756 5/19
Figure1 Experimentaldesignofascentandventingtreatments.(A)Illustratesdecompressionstopsforeachascenttreatment.Therateofascent
between stops was 0.25 m/s for all treatments. Fish subjected to ascent without decompression stops were brought directly to the surface. Fish
subjectedtoascentwithonedecompressionstopwerebroughttohalfthemaximumdepthfora45mindecompressionstop,thenbroughttothe
surface.Fishsubjectedtomultipledecompressionstopswerebroughtup3mevery15min.At10m(2atm),thesefishwerebroughtup1.5mevery
15min.(B)Ventingtreatmentschemeandfishsamplingdesign.Thisexperimentwasreplicated3timesforatotalsamplesizeofn=360fish.
Mundayetal.(2015),PeerJ,DOI10.7717/peerj.756 6/19
oftheholdingperiod.Serumcortisolconcentrationwasalsomeasureduponarrivalatthe
aquaculturefacility.Serumcortisolservesasaproxyforstressinfish(Donaldson,1981).
HOLDING PERIOD
Post-collection,fishwereobservedfor21datanaquaculturefacilitylocatedattheNatural
EnergyLaboratoryHawaiiAuthority(NELHA)inKona,Hawaiiprovidedwithnatural
surfaceseawateratambienttemperatures.Theexperimentaldurationwaschosenbecause
afterinterviewingfishersoperatinginKona,Hawaii,wedeterminedthat21drepresentsa
reasonabletimeperiodforafishtobetransferredfromthereeftoaretailerorhobbyistin
thisparticularchain.Inaddition,swimbladderhealinginrockfishhasbeenobservedafter
21d(Parkeretal.,2006)andissufficienttimetoallowskinandmuscleregenerationinfish
(Roberts,2010).Therefore,fishexhibitinglesionsafter21dmaynothavefullyrecovered
inasupplychainenvironmentandcouldbecategorizedashavingsublethaleffectsfrom
collection.
Fishwereheldin1mdiametermeshfloatingcageswithinthree10,000lpools,which
served as replicate blocks, each containing all six treatments. Incoming seawater was
filteredto5µm,andsettoflowthrougheachpoolatarateof1volume/d.Poolswere
exposedtonaturalsunlight,andtemperatureandsalinityweremeasuredtwicedaily.All
fishwerefedanaturalalgaediet(Ulvafasciata)richinnutrientsabsorbedfromfoodfish
outflowintheaquaculturefacilityforbiofiltration.
Fishweremonitoreddailyandmortalitywasrecorded.Standardlength(SL)(from
snouttobaseofcaudalfin)ofeachfishwasmeasured.Followingmortality,fishwere
placedin10%neutralbufferedformalinforhistopathology;theoperculumwasremoved
and body cavity opened to facilitate proper formalin fixation of the internal tissues.
Moribundfishwerehumanelyeuthanizedusinganoverdosesolution(>250mg/l)of
tricainemethanesulfonate(MS-222)(Sigma-Aldrich,St.Louis,Missouri,USA).
Histopathology
To determine the sublethal effects of collection methods, fish (n = 5) were chosen
randomlyfromeachreplicatetreatmentgroupimmediatelyuponarrivaltotheholding
facility(0d)andattheendoftheholdingperiod(21d)forhistopathology.Fishusedfor
histopathologywereeuthanizedusinganoverdosesolutionofMS-222,placedonice,and
shippedwithin48htoOregonStateUniversity’s(OSU)VeterinaryDiagnosticLaboratory
(VDL)forhistologicexamination.Fishthatdiedduringtheexperimentwerefixedin10%
neutralbufferformalinasdescribedaboveandexamined.
Formalin-fixedfishwereimmersedfor24hinCal-ExII(FisherScientific,Waltham,
Massachusetts,USA)todecalcifybone,andserialcrosssectionswereprocessedusing
standardhistologictechniques,sectionedat5µm,andstainedwithhematoxylinandeosin.
Brown-HoppsGramstainwasusedasnecessarytoassessforthepresenceofbacteria.All
slideswereexaminedusingaNikonEclipse50imicroscope(Nikon,Minato-ku,Tokyo,
Japan).Histologicexaminationfocusedupongill,heart,kidney,liver,swimbladder,and
intestine.
Mundayetal.(2015),PeerJ,DOI10.7717/peerj.756 7/19
Primary stress response
Becauseofthepotentialforcortisolconcentrationstodecreasewhenastressorsubsides,
bloodsampleswerecollectedfromfishimmediatelyuponarrivaltotheholdingfacility.
Fish(n=2)wereanesthetizedfromeachtreatmentreplicategroupusingMS-222prior
todrawing0.3–1.0mlbloodfromtheheartusinga25G2.54cmneedleand3mlsyringe.
Cardiacpuncturewasnecessarybecausethesmallsizeofthefish.Followingbloodsample
collection,fishwereeuthanizedusinganoverdosesolutionofMS-222.Todetermine
YellowTangoceanbaselinecortisolconcentration,bloodwascollectedfromfish(n=4)
underwateronSCUBAatcapturedepthwithin3minofcapture.Bloodwasinjected
into3mlvacutainertubeswithnoadditive(Becton-Dickinson,EastRutherford,New
Jersey,USA),placedonice,andcentrifugedat3,000rpmfor10min<1hlater.Serum
supernatantwastransferredtoacleanvacutainertubewithnoadditive,placedonice,and
frozen<1hlaterfor≤40dinanon-frostlessfreezer,andtransportedovernightondryice
totheOSUDepartmentofFisheriesandWildlifeforanalysis.
Serumcortisolconcentrationsweredeterminedusingradioimmunoassay(RIA)as
describedbyReddingetal.(1984).Totalbinding,theratiooftheradiolabeledcortisol
boundtotheantibodytothetotalamountofradiolabeledcortisolinthesample,was
40%–50%.Samplesshowedadequateparallelism,and3.9–500.0ng/mlcortisolstandards
wereused.
STATISTICAL METHODS
StatisticalanalyseswereperformedusingtheMinitab15StatisticalSoftwareprogram.
Tomeetassumptionsofnormalityandhomogeneityofvariance,dataweretransformed
tosquareroot(fishSL)orlog(cortisol).Aone-wayt-testwasusedtocomparemean
cortisolconcentrationsofeachtreatmentgroupwiththeoceanbaselineparameter.A
two-wayANOVAwasusedtocomparemeancortisolconcentrations,withdecompression
treatmentandventingasfixedfactorsandreplicateblockasarandomfactor.Tukey’s
multiplecomparisonstestwasusedtodeterminesignificantdifferencesbetweenlevels
withineachfactor.
RESULTS
Mortality
SizesofYellowTanginthisstudyrangedfrom5.0–10.0cmSLwithameanvalueof7.2cm
(SE=0.05cm).Mortalityoccurred<24hpost-collectioninfishsubjectedtoascent
withoutdecompressionstopsorventing,withameanmortalityof6.2%(SE=0.6%).No
mortalityoccurredintheotherexperimentaltreatments.
The incidence of mortality was consistent with observations of the frequency and
severityofexternalbarotraumasigns.Theseincludedhighfrequencyofpositivebuoyancy,
bloating, prolapse of the intestine from the cloaca, and exophthalmia (Fig. 2) in fish
subjectedtoascentwithoutdecompressionstops.Ventingrelievedpositivebuoyancy
andventedfishbecameneutrallyornegativelybuoyant(Fig.2).
Mundayetal.(2015),PeerJ,DOI10.7717/peerj.756 8/19
Figure2 BarotraumasignsobservedinYellowTangfollowingcollection.(A)Positivebuoyancybefore
ventingandneutraltonegativebuoyancyfollowingventing(B)intestinalprotrusionfromthecloacaand
(C)exophthalmia.
Mundayetal.(2015),PeerJ,DOI10.7717/peerj.756 9/19
Histopathology
Histopathologyofgill,heart,kidney,liver,swimbladder,andintestinefailedtodetect
significantinflammation,necrosis,orgasembolismassociatedwithbarotraumaorventing
inanytreatment,inboththeshort-andlong-term.Aventingwoundwasdetectedina
fishsubjectedtoascentwithmanydecompressionstopsandventingatday0.However,
thislesionconsistedonlyoflocallyextensivenecrosisofbodywallmusculatureanda
localizedinfluxofneutrophilssurroundingtheneedletrackandnotsignificantwidespread
infection(Fig.3).
Primary stress response
Themeanoceanbaselinecortisolconcentrationwas8.9ng/ml(SE=4.96ng/ml)and
insomecaseswasatorbelowthedetectionlimitfortheassay(3.9ng/ml).Alltreatment
groupsweresignificantlyelevatedabovethebaselinecortisolconcentration(One-way
t-test;p<0.05).Therewasnosignificantinteractionbetweendecompressiontreatment
and venting. Decompression treatment significantly affected cortisol concentration
(Two-wayANOVA:F=4.26;df =2,12;p=0.03)(Fig.4).Ascentwithoutdecompression
stopsresultedinasignificantlyhighermeancortisolconcentration(M =58.8ng/ml,
SE=8.7ng/ml)thanascentwithmany15mindecompressionstops(M =35.5ng/ml,
SE=5.3ng/ml),withneithertreatmentbeingsignificantlydifferentfromascentwithone
45mindecompressionstop(M=35.2ng/ml,SE=4.3ng/ml).Ascentwithoutdecompres-
sionstopsproducedthehighestobservedcortisolconcentration(101.49ng/ml),whereas
thehighestobservedcortisolconcentrationsinfishsubjectedtooneandmanydecompres-
sionstopswere59.09and68.03ng/ml,respectively.Whileventingresultedinhighermean
cortisolconcentration(M =47.7ng/ml,SE=6.9ng/ml)thanthenoventingtreatment
(M=38.2ng/ml,SE=4.3ng/ml),thisdifferencewasnotstatisticallysignificant.
DISCUSSION
Withtheobjectiveofinformingmanagementoncollectionpracticesintheaquarium
trade,ourstudyfocusedontheshort-andlong-termmortalityofreeffishsubjected
to decompression and venting as barotrauma prevention and mitigation practices,
respectively. Overall, we found that venting prevented immediate mortality in fish
subjectedtoascentwithoutdecompressionstops.Ascentsignificantlyelevatedserum
cortisolabovebaselineconcentrations,andascentwithoutdecompressionstopsresultedin
significantlyhigherserumcortisolconcentrationsthanascentwithmanystops.Venting,
however,didnotsignificantlyaffectcortisolconcentration.Inthefollowingsections,we
explainourresults,suggestfutureresearchrecommendations,anddiscussimplicationsfor
managementofthisfishery.
Mortality
Wefoundthatthemethodscommonlyusedinthisfishery(ascentwithoutdecompression
stops, or ascent with one decompression stop, followed by venting) resulted in no
immediateordelayedmortality.Ascentwithoutdecompressionstopsfollowedbyventing
resultedinnomortality,whilefishsubjectedtoascentwithoutdecompressionstopsand
Mundayetal.(2015),PeerJ,DOI10.7717/peerj.756 10/19