Introduction Closingthecycleofcommerciallyexploitedfishina recircu-latingaquaculturesystemisgrowinginimportanceforavariety ofreasonsthatincludeovercomingthedifficultiesingettinglive broods
Trang 1j ou rn a l h o m e p a g e :w w w e l s e v i e r c o m / l o c a t e / a q r e p
Saleem Mustafa∗, Mohd Hafizzie Hajini, Shigeharu Senoo, Annita Yong Seok Kian
Borneo Marine Research Institute, Universiti Malaysia Sabah, Kota Kinabalu, Sabah 88400, Malaysia
a r t i c l e i n f o
Article history:
Received 9 February 2015
Received in revised form 5 August 2015
Accepted 18 September 2015
Available online 28 September 2015
Keywords:
Tiger grouper
Broodstock
Conditioning
Socio-demographic cues
Intrinsic factors
Sex reversal
a b s t r a c t
1 Introduction
Closingthecycleofcommerciallyexploitedfishina
recircu-latingaquaculturesystemisgrowinginimportanceforavariety
ofreasonsthatincludeovercomingthedifficultiesingettinglive
broodstockfromthewild, exorbitantcost,biosecurityproblems
andimpactonthemarineecosystem
Inahatchery,closingthelifecycleoftigergrouper(Epinephelus
fuscoguttatus)thatrequiresseveralyearstomatureandis
protog-ynoushermaphrodite,presentssomechallenges.However,since
adequatesupply of high-qualityseedof this species isa major
constraintfacedbytheaquacultureindustry,especiallythe
small-and-mediumenterprises,thesechallengeshavetobeaddressed
Seedqualitydependsheavilyonbroodstockcondition.While
temperatureandphotoperiodarethetwomainenvironmentalcues
thatcontrolthereproductivecycle(Sudaryantoetal.,2004)other
factorsincludingthenutritionalstatus,and parameterssuchas
salinityanddissolvedoxygendoinfluencethephysiological
con-ditionofthefish(Simetal.,2005;Sugamaetal.,2012).Anideal
∗ Corresponding author Fax: +60 88 320261.
E-mail addresses: saleemacademic@gmail.com , Saleem@ums.edu.my
(S Mustafa).
broodstockmanagementenvisagesmimickingtheconditionsthat thefishfacesinitsnaturalenvironment.Becausetheselected spec-imensofthefishwereproducedinthehatchery,theyarealready accustomedtocultureconditionsandthereforeeasiertodevelop intobroodstockcomparedtotheirwildcounterpartsorparentsof thiscohortsourcedfromthewildpopulations
Thisstudywasundertakenfordeterminingtheoptimum con-ditionsfordevelopingtigergrouperbroodstockbyenvironmental controlsaimedat stress reduction andbalanced nutrition Pro-ductionofseedbyspawningoftheenvironmentallyconditioned captivebroodstockhasmanyadvantagesoverspawninginduced
byhormoneinjection.Hormonetreatmentcausesstressof han-dling,injection,and/orimplantationofexogenoussubstances,and producessideeffectsaswell.Thispaperpresentsdataonthe posi-tiveeffectsofeffectivelycontrollingbroodstockrearingconditions forgrowthanddevelopmentofgonads
2 Materials and methods
ThisexperimentwascarriedoutatthefinfishhatcheryofBorneo Marine ResearchInstitute, UniversitiMalaysia Sabah,Kota Kin-abalu.Broodstockareaofthehatcherywascoveredwitharoof butthesideswereopen,allowinglighttoenter.Noartificiallight wasusedtomanipulatethephotoperiod.Eachtankwasof150m3 http://dx.doi.org/10.1016/j.aqrep.2015.09.004
2352-5134/© 2015 The Authors Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.
Trang 2capacity,roundin shapeand medium-rangeblueincolor.Tank
of this volume is consideredideal for broodstockmanagement
inthehatcheries Itprovidesadequatespaceforswimmingand
specificcourtshipbehavior.Thisisconsistentwiththesuggestion
ofSugamaetal.(2012)regardingthetanksize,shapeandcolor
(preferablymedium-rangeblue,greenorgraycolorandavoiding
shadesthatareeitherverylightorverydark)
Specimensofthetigergrouperwhichvisiblylookednormalin
bodyshapeandcolor,appearedhealthythroughgeneralactivity
(swimming,feedingandquickresponsetoexternalstimuli)and
whichweredevoidofanyskeletalabnormalitiesorexternalsignsof
infectionorinjurywereselectedaspotentialbreedersforthetrials
Thesespecimenswereproducedinthesamehatcherybyselective
breedingoffounderstockthat originatedfromwildpopulation
Thetestspecimens(broodstockcandidates)belongedtothefirst
generationofthehatchery-producedfish.Sixty-eightspecimens
oftigergrouperofaveragetotallength=65.2±11.2cmandbody
weight=5601±2699gwererearedfortrialsconductedin
brood-stocktanks.Fishwereequallydividedinthetwotanks.Maintaining
waterqualityconditionsinsuchlargetanksischallengingbut
man-ageablegiventheadequatesupplyoffilteredseawater,aeration
andairliftpumps.Tankswereprovidedwithwaterrecirculation
systemandthefishwereobservedthroughsidewindows.Tanks
receivedwaterfilteredbydynasandfiltrationsystemthatensured
removalof solids.Nitrogenous wastes inthe formof ammonia
andnitritewerecontrolledbybiofiltersinanadjoiningtankthat
containedsubstratesforcolonizationofnitrifyingbacteria
(Nitro-somonasandNitrobacter).Aeratorswereusedtohelpincirculation
ofdissolvedoxygenandeliminationofnitrogenouswaste
Tem-perature,salinity,pH,dissolvedoxygen,nitriteandammoniawere
routinelymonitored
Thefishspecimenswereofferedfeedcontainingpreyfishthrice
aweekattherateof3%bodyweightwhichprovidedabout50%
protein(dryweightbasis).Thistreatmentofthefishcontinuedfor
6monthsduringwhichtheirgrowth,somaticconditionandsigns
ofsexdifferentiationwererecorded.Fishweregenerallyobserved
daily,particularlyatthetimeoffeedingbutmeasurementswere
takenonaweeklybasis.Asamatteroffact,theexperimentstarted
withthesame-sexspecimensofthisprotogynoushermaphrodite
fish.Forthespecificpurposeofnoticingsexdifferentiation,
obser-vationsonanychangeinthebehaviorwerecarriedout
Length–weightrelationshipwasestablishedbyusingthe
stan-dardallometricequation:W=aLb,where,W=weight(g),L=total
length(cm),a=constant(interceptinthegraph)andb=exponent
(slopein thegraph).Thisequationis for anon-linear situation
which does not offer a direct solution for interpretation of ‘a’
and‘b’.Itwas,therefore,logarithmicallytransformedforalinear
regressionmodel:logW=loga+alogL,whereloga=constantand
b=exponent.Thisequationcanbeusedforpredictingthelogarithm
ofweightasafunctionofthelogarithmoflength
Conditionfactor(K)wascalculatedbytheformula:K=100W/L3,
where,W=bodyweightofthefish(g)andL=totallength(cm)
3 Results
achieve water quality parameters in the tanks in the range:
salinity=29.7–31.0‰, temperature=26.4–28.9◦C, dissolved
oxy-gen=5.8–6.4ppm and pH 7.2–7.5 The nitrogen-nitrite and
unionized ammonia never exceeded 0.05ppm and 0.02ppm,
respectively
Analysisof length–weightregression produced theformula:
logW=−1.5855+2.9185logL(Fig.1).Thecorrelationcoefficient,
R2(0.9501)wassignificantlyhigh(P<0.005),suggestingasteady
progressionofthetwogrowthparameters.Theexponent(b)value
y = 2 9185x - 1 5855 R² = 0 9609
3.00 3.20 3.40 3.60 3.80 4.00 4.20
1.65 1.70 1.75 1.80 1.85 1.90 1.95 2.00
Log L (cm) Length Weight Rel ationship
Fig 1. Length–weight relationship in tiger grouper, Epinephelus fuscoguttatus.
of2.9185indicatednomajordeparturefromthecube-law relation-shipbetweenlengthandweightalthoughtechnicallyspeakingany valuelessthanthree(>3)characterizesnegativeallometricgrowth thatimpliesthatthefishbodyprofilebecameslightlymoreslender
asitgrew.Theconditionfactor(average=1.86)waswithinthe nor-malrangeforahealthytigergrouper,reflectingthatthefishwerein
agoodsomaticconditionasaresultofthefavorableenvironmental conditionsandappropriatefeedingregime
Thestockedfishstartedwithfemalesexbut5outof68 speci-mensshowedmale-likebehavior
4 Discussion
Itisevidentfromthegrowthexponentinthelength–weight relationshipandtheconditionfactorof thegrouperstocksthat thehatcheryprovidedsuitablecultureenvironment.Thisaugurs wellforbroodstockmanagement,especiallygrowth,gonad devel-opment,fecundity,eggqualityand exercisingcontrolontiming
ofmaturationandspawning.Itisnotuncommonforfishreared
inhatcheriestosufferfromreproductivedysfunctionandlossof fertilityifcaptivityconditionsarenotproperlymaintained.Tank size, shape and colorare important in maintainingbroodstock forextended periodsin thehatchery Adequatespacefor large-sizedfishlikegrouperisnecessaryespeciallyforcourtshipthatin thisspeciesisnecessaryforbreeding.Whilediscussingthistopic Benetti(2002)hasemphasizedthatthelargerthefish-holdingarea, thebetteritisforthefish.Tanksof150-toncapacityusedinthis trialtogetherwitheffectivecontrolonwaterqualityandnutrition wereamongthemaincontributingfactorsforthewellbeingofthe captivestocks
Beingaprotogynoushermaphroditethetigergrouperstartsits earlyphaseoflifeasafemaleandatalateragesomespecimens changesextobecomemale(Pearsetal., 2007).It is,therefore, expectedthatfemalesoutnumberthemalesandthesexratioto
behighlyskewedtowardthefemalesexevenafterdifferentiation
ofafractionofthepopulationintomale.Therearemanyviewson whattriggerssexreversalbutitisunderstoodthatthefactorsmay
beinternal(intrinsic)orexternal(extrinsic).Inthenatural environ-ment,sexchangeingroupersisknowntooccurduringspawning aggregationforreproductivesuccessandifatthattimethescarcity
ofmalesbecomesalimitingfactor,somefemalesswitchoverto malesextoensurethatbreedingandpopulationrecruitmenttake place.Generally,thedominantfemalesundergothissortofsex con-version.Adifferentsituationprevailsinthehatcherytanks.The socialandenvironmentalcuesinthehatcheryaredifferent.Also, thereisnoaggregationdrivenbynaturalinstinctandurgetomate similartowhatprevailsinnature.Fishmovingoverlongdistances
intheirnaturalenvironmentforaggregationwiththepurposeto matewillcertainlybemorevigorousinthisactivityandtheir hor-monalturnoverwillbequantitativelydifferentfromstocksheld
Trang 3restrictedarea,whileinnaturetheydonotliveingroups.Obviously,
thereissomesocialinteractionasamatterofroutinewhileliving
overextendedperiodsandthisperhapscandiminishtheintensity
ofmatingandreproductiveactivityseeninthewild.Thedesireto
mateisinstinctiveandmotivatedbyphysiologicalfactorsbutsocial
andenvironmentalfactorshaverolestoplay.Theexactnatureof
thecomplexcuesandtheleveloftheirinfluenceonsexualityare
difficulttounderstand
Thetestspecimensstockedintanksweremixedagegroups
Theywereallfemalesduetoprotogynousconditionofthisfish
Evenwhennofunctionalmalewasintroduced,atendencyin a
smallnumberofthesespecimenstoturnintomalewasnoticed
Whenafunctionalmalewasintroduced,itdidnotseemtoproduce
anyeffectonsextransformationasthenumberdidnotchange
ThisviewisatvariancewiththatofSugamaetal.(2012)who
sug-gestedthatthepresenceoffunctionalmalefishcouldrepresssex
changebythefemale.Itislikelythatafunctionalmaledoesnot
makeanysignificantimpactwhendominantfemaleshavealready
startedtransitioningtomalesex.Changeinthesexthatoccurredin
5ofthe68specimenexaminedindicatedthatevenintheabsence
ofthemalesthecuesareatworktotriggerthelargersizedfish
ofmatureagetobecomemale.Thiscouldbeattributedto
socio-demographiccuethatisanexternalfactor.Sugamaetal.(2012)
havedocumentedthatsexchangeintigergrouperinbroodstock
tanksissociallymediated.Totheextentthatthesexreversalonly
involvedfishof4–5yearsofage,itseemstobeage(orsize)-related
whichisendogenouslycontrolled.Youngerfishof2–3yearsofage
showednoevidenceofsexreversal,soapparentlytheperception
ofsocialcuesdependsonageorinternal(physiological)condition
ofthefish
Signsofsexdifferentiationobservedwereintheformofchange
inbehavior.Thisincludedonsetofmale-likebehavior,increased
patrollingoftheentiretank,shakingofheadandvigorous
swim-mingwheninclosevicinityoffemaleconspecifics.Itisexpected
thatthischangeinbehaviorisundertheinfluenceofincreasein
malesexhormones.While behavioralchangecanhappenmuch earlierthanthecompletetransitionofthegonadfromovaryto testis as it involves modification of gonad morphology and its steroidogeniccapacity.Thefishcanbecomeatrulyfunctionalmale uponcompletionofthisprocess.Howlongittakestoachievethis stageisaninterestingtopictopursue
Probably,thisisthefirstreportofitskindontigergrouperthat providesaconvincingexplanationoftheroleofbothinternaland externalfactorsinsexdifferentiationintigergrouperinthe hatch-ery tanks.Attainingfunctionalfemaleand malestatusby these specimenswilldefinethesuccessoftheclosedcycleaquaculture
oftigergrouper
Acknowledgement
ThisstudywasfundedbytheMinistryofEducationofMalaysia undertheHigherInstitutions’CenterofExcellence(HICoE) pro-gram
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