July | August 2012

Noise a source of stress for farmed fish

The International magazine for the aquaculture feed industry

International Aquafeed is published five times a year by Perendale Publishers Ltd of the United Kingdom.All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies, the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of information published. ©Copyright 2012 Perendale Publishers Ltd. All rights reserved. No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1464-0058

It iswidely recognised that fishwelfareandstressareinextricablylinked.Whenwelfare is compromised and fish areunder stressful conditions there are a

widerangeofnegativeeffectsthathavebeenreported.These includeareduction in feedintake, growth, food conversion efficiencyandfleshquality;an increase indiseasesus-ceptibility and aggression; disruption of thereproductiveaxisandultimately,inextremecasesmortality.

Researchhas focusedonnumerousdiffer-entpotentialstressorsincludingenvironmentalfactors such as light, temperature and waterqualityaswellasphysicalstressorslikecrowd-ing,handlingandtransportation.However,thepotential for sound to act as a stressor hasbeenlargelyoverlookedinaquaculture.

The importance of soundSound plays an important role in the life

of terrestrial andaquatic animals as ameansofcommunicationaswellasitsroleinecho-location,predatoravoidance,orevenjusttheperception of changes in the environment.As such it deserves greater attention thanit has received so far as a parameter to bemonitored/managedinculturesettings.

Itmustbeacknowledgedthatairandwateraretwocompletelydifferentacousticenviron-ments. With water being athousand timesdenser thanair, a greater energy inputis required to initiate soundpropagation which resultsin sound underwater hav-ing a greater velocity withless attenuation. In practicaltermsthismeansthatgreat-erenergyisrequiredtocastanoiseunderwateralthoughwater is less restrictive toaspreading sound wave, andthus aquatic fields can beverynoisyenvironments.

The concept of sound

involvesaseriesofcomplextermsbutessen-tiallysoundisenergytravelingasamechanicalwavecausedbychangesinthemediumpres-sure.Detectionof those variations is knownastheaudiblesoundanditsloudnessdependson the specific sensitivity to the frequencies.Thecolloquialterm‘soundvolume’oftencon-foundsthedefinitionsofsoundpressureandsoundintensity:soundintensity istherateofflowofenergythroughanarea(W/m²),whilesoundpressureisthe‘strength’ofthesoundwave (Pa). Sound pressure levels (SPL) arethelogarithmicexpressionintherelativescaledecibel(dB)oftherootmeansquare(RMS)compared to a reference value. Thus, toquantifyanthropogenic sounds in thecultureenvironment,weusetheSPLofagivennoiseoverthebackgroundreference.

Sound perceptionAquaticanimalsareprovidedwithawide

range of sensory organs and systems toperceive and filter relevant environmentalsignals. The capability of fish to cast andrecognise sound is well documented forsome species, showing significant variabilityamongthem.

In general, sound perception in fish islocalised to three interconnected systems:the auditory, the equilibrium and the lateralline.Theyinvolveaseriesofcomplexorgans

or tissues and specialised cells distributedthroughouttheanimalbody,givingthefishtheabilitytosenseanddiscriminatesoundsbasedontheirdirection,distanceandsource.

Fish auditory thresholds are believed tobeprimarily in the rangeof20 to3,000Hz.However sensitivity does clearly vary withspecies(Figure1)andstageofdevelopment.Reportshaveindicatedthatsomefishspeciescouldevendetectverylowfrequenciesintheinfrasoundrange(<20Hz)aswellaspossiblyin the ultrasound range (>20 kHz) althoughthis may depend on sound levels fish areexposedto.Whetherfishperceptionofthesesoundfrequencies is functionalhearingoranartefactofpast auditory requirementsneedsfurtherclarification.

‘Grunts’ and ‘clicks’Fish do not only passively perceive

soundsgeneratedintheirenvironment,theycanalsobevocallyactiveasshowninmanyspecies. The swim bladder has an audi-toryaccessoryfunctionreflectingsoundandamplifying theircommunications.Some fishalsousethis‘soundbox’togeneratevocali-sations for a variety of potential reasonsincluding maintenance of contact, warningof predators, aggression or mate choice.Atlanticcod(Gadus morhua)isaparticularlyvocalspecieswhichproducessoundsduring

aggression, chasing, escapingbutmainlyduringcourtship.

Cod vocalisations arenamed ‘grunts’ and ‘clicks’based on the human percep-tionofthesound.The ‘grunts’are produced by repeatedlycontracting the drum musclesendingvibrationstotheswimbladder.Onegruntisarepeti-tion of single pulses of 60 to200 ms in frequencies rangingfrom30to250Hz(Figure2).

It is believed that duringcourtship females will assessthe fitnessof themales based

Noise a source of stress for farmed fishBy Rogelio Sierra Flores1 2, Andrew Davie1, Tim Atack2 and Herve Migaud1, Institute of

Aquaculture, University of Stirling, UK and Ardtoe Marine Laboratory, UK

Figure 1: Hearing thresholds comparison of humans, dogs, bats and fish. Hearing thresholds for five selected fish species (Atlantic cod, Atlantic salmon, Common carp, Tunids, and goldfish) Adapted from Popper et al., 2008

28 | InternAtIonAl AquAFeed | July-August 2012

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July-August 2012 | InternAtIonAl AquAFeed | 29

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on their grunting. As such, male gruntingvigourhasbeenrelatedtothevolumeofthedrummusclemass aswell as the individual’sspecificimmunecondition.Duringmatingthefemalewillsettleontheground,whilemales‘perform’ a courtship characterised by bothvocalisationsandaswimmingpatternaroundthefemale.

Inenclosedaquaculture systems it is verylikely that mating performance/mate choicecould be impaired if the males ‘singing anddancing’performance is somehowrestrainedbythephysicalconditions.Whileeveryefforthas been directed to optimising broodstockholding tanks to ensure enough space andlowturbulences toallowpairedmating, littlethoughthasbeenputintotheacousticcondi-tionsexperiencedbyfishinculture.

Negative effects of soundThe negative effects of anthropogenic

sound are well documented in the naturalenvironmentwhere awide range of specieshavebeenshowntoaltertheirnaturalcom-munication and behaviour with there evenbeing evidence of panic and confusion inresponse to different anthropogenic soundstimuli. In the natural marine environmentthese sound sourcesarediverseand includeoffshoreengineering,piledriving,seismicsur-veying, busy shipping areas as well as navalactivity.

Incaptivitysoundsourcesaremorespe-cific, being related to the general operationofanaquaculturefacilityincludingequipmentand general husbandry activities. Literaturesuggeststhatgeneralactivityandfarmnoisewill generate low frequency vibrations i.e.<1kHz which is within the auditory sensi-tivity of fish. Thus,priortoquantifyinghow sound couldact as a stressor,it was felt impor-tant to more pre-ciselycataloguethesound-scape in atypical land-basedaquaculturefacility.

A sound map-ping exercisewas performedin the facilities ofArdtoe MarineLaboratory inScotland whichrevealed a surprisingly quiet backgroundsound level in the rearing tanks as com-pared to what would be expected inshallow coastal waters. That said, sounddisturbanceswereevident.Commonhus-bandry activities like hand feeding, walk-ing, hand netting, talking, water inflow,aeration bubbles, and knocks against the

tank walls all create obvious perceptiblenoise (Figure 3). Some basic activitieslike hand feeding showed a low soundlevel increase of 8-11 dB re µPa abovebackgroundnoise.

However, the analysis showed thatotherdaily activities can reach worrying levels.

Accidentaland/orintentionalknocksagainstatankwall,whichcancausestrongbehaviouralreactions in the fish stocks, generates lowfrequencysoundswithvolumesrangingfrom21-39 dB depending on the vigour/cause ofthe perturbation. Such SPL are clearly per-ceivedbythefishandcouldpossiblytriggerastressreaction.

Figure 2. Waveform and spectrogram of four different cod grunts recorded in the facilities of Ardtoe Marine Laboratory, Scotland during Spring 2010.

28 | InternAtIonAl AquAFeed | July-August 2012 July-August 2012 | InternAtIonAl AquAFeed | 29

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projectincludedfourtilapiafarmsinChina.Thesefarms represented both small- and commercial-scale production facilities utilising two differentproductionsystems(pondandcages).Asidefromidentifyingsimilaritiesanddifferencesamongcriteriaand requirements used by the three standards,thisprojectalsoidentifiedoutstandingissuesinthefarms,whichmostproducerswereabletoaddressasaresultofthetrialaudit.Todate,allfourfarmsarenowcertifiedunderoneormoreofthecom-mercialaquaculturestandards.

SFP is widely acknowledged for its expertiseby stakeholders in Chinese tilapia, including keyUSandEuropeanbuyersandretailers,aswellasproducers and processors in China, aquacultureinstitutes, industry associations, and localChinesegovernments.GiventhehighleveloftrustthatSFPenjoyswiththetilapiasupplychainitwasappropri-atethatatilapiaAquacultureImprovementProject(AIP)wasofficiallylaunchedin2011.

SFPhasnowinitiatedtworesearchprojectstoassess the impactof tilapia farmingon theexternalenvironment.Thefirstproject,startedinApril2011, involvesmonitoringwaterqual-ityonselected farms inHainanprovince,andwas undertaken by the Hainan Institute ofAquaculture.Dozens ofwater quality param-eterssuchaschemicaloxygendemand(COD),nitrogen and phosphorus content, and heavymetalswereanalysed for five farmsover twocroppings (10 months). The study helped

identifythekeyproblemsandcausesrelatedtowatermanagement.

The second project is an assessment of theregionalenvironmentalimpactsoffishfarmclusters,whichwillbejointlyconductedbySFPandHainanResearchAcademyofEnvironmentalSciences,theleadingenvironmentalresearchinstituteinHainan.Thestudywillexaminethepotential forregionalscaleimprovementbylookingatcarryingcapacityandthepotentialforzoninginaspecificarea.

As more first-hand data becomes available(along with a more in-depth understanding ofexistingpoliciesandmanagementmeasures), theAIPwillestablishaworkinggroupthatconvenesthekeybuyers,suppliersandproducersalongtheChinesetilapiasupply-chaintosharethescientificfindings.TheAIPwillthenformamulti-stakeholderpolicyroundtabletofurtherdiscusstheproblemsandsolutions.TheAIPparticipantswilleventuallyagreeontheactionsandtimetablesnecessarytoachieve the sustainability objectives defined bythegroup.SFPwillplayaleadingroleinengagingstakeholders,providingscientificadviceandfacilitat-ingcommunication.

Up-to-date progressSFPhasworkedcloselywithlocaltilapiaassocia-

tions to assessdifferent tilapia standards that areavailable in the market. A workshop introducingthreeinternationalstandardsfortilapiafarming,i.e.BAP,GlobalGAP, andASC,was held inHaikou

inApril,2011.Over40farmers,processors,tech-nicians and government officers attended theworkshop.Participants found theworkshopveryinformativeandhelpful.Thisenhancedtheproduc-ers’awarenessofincreasingdemandsforcertifiedsustainable seafood from overseas markets, thusfurther facilitating the engagement of Chinesestakeholders into a supply-chaindialogue aroundsustainability.

SFPiscurrentlyworkingwithlocalinstitutesofaquacultureandenvironmentalsciencestoidentifyand evaluate both qualitatively and quantitativelythe environmental impacts of tilapia farming inHainan.Thisincludesanecologicalstudyaswellassocio-politicalanalysistoadviselocalgovernmentsandindustrialassociationsabouthowtoefficientlyaddress theenvironmental issuesassociatedwithtilapiafarminginHainan.ThepreliminaryresultswillbesharedwithkeystakeholdersattheAquaculturePolicyRoundtablethisfallinChina.

SFP is also developing partnerships withChineseuniversitiesandlargefeedmanufacturersto improve feed sourcing for tilapia farming inChina. This work is to be undertaken throughresearch projects on improving feeding efficien-cy and developing alternative feeds with fewerimpactsonwildfisheries.

More InforMatIon:Sustainable Fisheries PartnershipWebsite: www.sustainablefish.org

26 | InternAtIonAl AquAFeed | July-August 2012 July-August 2012 | InternAtIonAl AquAFeed | 27

EXPERTT●PIC

projectincludedfourtilapiafarmsinChina.Thesefarms represented both small- and commercial-scale production facilities utilising two differentproductionsystems(pondandcages).Asidefromidentifyingsimilaritiesanddifferencesamongcriteriaand requirements used by the three standards,thisprojectalsoidentifiedoutstandingissuesinthefarms,whichmostproducerswereabletoaddressasaresultofthetrialaudit.Todate,allfourfarmsarenowcertifiedunderoneormoreofthecom-mercialaquaculturestandards.

SFP is widely acknowledged for its expertiseby stakeholders in Chinese tilapia, including keyUSandEuropeanbuyersandretailers,aswellasproducers and processors in China, aquacultureinstitutes, industry associations, and localChinesegovernments.GiventhehighleveloftrustthatSFPenjoyswiththetilapiasupplychainitwasappropri-atethatatilapiaAquacultureImprovementProject(AIP)wasofficiallylaunchedin2011.

SFPhasnowinitiatedtworesearchprojectstoassess the impactof tilapia farmingon theexternalenvironment.Thefirstproject,startedinApril2011, involvesmonitoringwaterqual-ityonselected farms inHainanprovince,andwas undertaken by the Hainan Institute ofAquaculture.Dozens ofwater quality param-eterssuchaschemicaloxygendemand(COD),nitrogen and phosphorus content, and heavymetalswereanalysed for five farmsover twocroppings (10 months). The study helped

identifythekeyproblemsandcausesrelatedtowatermanagement.

The second project is an assessment of theregionalenvironmentalimpactsoffishfarmclusters,whichwillbejointlyconductedbySFPandHainanResearchAcademyofEnvironmentalSciences,theleadingenvironmentalresearchinstituteinHainan.Thestudywillexaminethepotential forregionalscaleimprovementbylookingatcarryingcapacityandthepotentialforzoninginaspecificarea.

As more first-hand data becomes available(along with a more in-depth understanding ofexistingpoliciesandmanagementmeasures), theAIPwillestablishaworkinggroupthatconvenesthekeybuyers,suppliersandproducersalongtheChinesetilapiasupply-chaintosharethescientificfindings.TheAIPwillthenformamulti-stakeholderpolicyroundtabletofurtherdiscusstheproblemsandsolutions.TheAIPparticipantswilleventuallyagreeontheactionsandtimetablesnecessarytoachieve the sustainability objectives defined bythegroup.SFPwillplayaleadingroleinengagingstakeholders,providingscientificadviceandfacilitat-ingcommunication.

Up-to-date progressSFPhasworkedcloselywithlocaltilapiaassocia-

tions to assessdifferent tilapia standards that areavailable in the market. A workshop introducingthreeinternationalstandardsfortilapiafarming,i.e.BAP,GlobalGAP, andASC,was held inHaikou

inApril,2011.Over40farmers,processors,tech-nicians and government officers attended theworkshop.Participants found theworkshopveryinformativeandhelpful.Thisenhancedtheproduc-ers’awarenessofincreasingdemandsforcertifiedsustainable seafood from overseas markets, thusfurther facilitating the engagement of Chinesestakeholders into a supply-chaindialogue aroundsustainability.

SFPiscurrentlyworkingwithlocalinstitutesofaquacultureandenvironmentalsciencestoidentifyand evaluate both qualitatively and quantitativelythe environmental impacts of tilapia farming inHainan.Thisincludesanecologicalstudyaswellassocio-politicalanalysistoadviselocalgovernmentsandindustrialassociationsabouthowtoefficientlyaddress theenvironmental issuesassociatedwithtilapiafarminginHainan.ThepreliminaryresultswillbesharedwithkeystakeholdersattheAquaculturePolicyRoundtablethisfallinChina.

SFP is also developing partnerships withChineseuniversitiesandlargefeedmanufacturersto improve feed sourcing for tilapia farming inChina. This work is to be undertaken throughresearch projects on improving feeding efficien-cy and developing alternative feeds with fewerimpactsonwildfisheries.

More InforMatIon:Sustainable Fisheries PartnershipWebsite: www.sustainablefish.org

26 | InternAtIonAl AquAFeed | July-August 2012 July-August 2012 | InternAtIonAl AquAFeed | 27

EXPERTT●PIC

Fish reactionStressreactionsinfishinresponsetosound

perturbations can be behavioural, acousticand/or physiological. Behavioural responsesaretheapparentavoidanceor freezingreac-tion.Acousticresponsesaremoredifficultto

characterise,howeverevidence suggests thatfish may attempt to alter their vocalisationform and structure (length, frequencies andamplitude)to increasetransmissionprobabil-ityashasbeenreportedinothervertebrates.

Finally, the physiological responses arevariedasastressactivationofthesympatheticnervoussystem(SNS)andthehypothalamic-pituitary-interrenal (HPI) axis can impact onmanyprocesseshoweverevidenceof soundstimulatingtheseprocessesis lackingtodate.Buscaino et al. (2009) demonstrated in seabassandseabreamthatsoundperturbationsaboveathresholdcanresultinanincreaseinblood glucose levels and haematocrit whichconfirms the involvement of the HPI axis inthisspecies.

Acute stress response Our studies have shown that noise does

elicitanacutestressresponseinAtlanticcod(Gadus morhua) juveniles. Fish exposed tosound in the100-1000Hz range for10min-utes,usingsuspendedunderwaterloudspeak-ers, showed a significant increase of plasmacortisol concentrations within 10 minutes ofexposure.

Furthermore, the response was dosedependentassoundpressurelevelsweredirect-

ly correlated to peak cortisol concentrations.Testedsoundlevelswerecomparabletothoseencountered during the site sound mapping,whichsuggeststhataperturbationassimpleasknocking a tankwall canbe strongenough totriggerasignificantincreaseofcortisol.

Recovery from the sound perturbationwas also rapid indicating it to be an acutestress response that fish should be able tocopeandadaptto.Thiswouldinturnsuggestaminorimpactinthelong-termperformanceof the fish stocksalthough, in fish farm facili-ties, thoseacutesuddennoisesarecommonand frequent.Thus, thesecondphaseof thework considered how short ‘acute’ soundstressorsappliedovera longtime framecanimpactonfishperformances.

Sound stressors over time: a significant impact

We discovered that cod broodstockexposed to six hours of daily randomisednoiseataSPLof34dBreµPa(comparableto a loud knock on a tank wall) significantlyimpacted on the their spawning perform-ance. Egg production in terms of volume ofeggs and egg size was comparable betweenbroodstocks that were both exposed, andnot exposed, to sound though in the soundexposed population fertilisation rates werereducedbyalmosthalf.

Workiscurrentlyunderwaytoinvestigatewhysoundperturbationsresult insuchasig-nificant reduction in fertilisation successwithone possibility being the maternal transfer

of elevated cortisol to the oocytes reducingtheir viability. Another possibility is that thecourtshipritualcouldhavebeendisruptedbytherandomisedsoundexposuremaskingthegruntsand interrupting thematingbehaviourexplaining the reduction in fertilisation rate.Regardless of the causative mechanism, thefact that fertilisation success and egg qualitywere so clearly affected in sound stressedbroodstockshouldbetakenasaclearindica-tiontheacousticconditionsinculturedeservemoreattention.

Implications for other species WhileevidencesuggeststhatAtlanticcod

is oneof themore acoustically sensitive fishwe firmly believe that there are implicationsforthiswork inmostotherculturedspecies.Future work should focus on the long-termeffects of noise as a stressor including tem-poraryauditorythresholdsadaptationascop-ing strategies. Acclimatisation to noise mightbe possible, although negative physiologicalresponses could be present even without aclearbehaviouralresponse.

In terms of the culture facilities we use,clearly more attention has to be paid inreducingthenoisecausedaroundland-basedaquaculturefacilitiesand,bydoingso,makingaquaculture production more reliable andpredictable possibly helping to reduce thecommonlyreportedvariabilityinfishperform-ancesinmostaquaculturefacilities.

Instituting some routine simple andcheap sound measurements on a farmcould mitigate many unnecessary distur-bances that might be acting as stressorsaffecting thewelfareandthusperformanceofthefish.Theresultsofdoingsomaywellbeseeninthebottomline. ■

Acknowledgments

Thisprojectwasco-fundedbytheMexicanCouncilforScienceandTechnology(CONACYT)andEUFP7project232305“PROSPAWN”.

References

Buscaino,G.,F.Filiciotto,etal.(2010)."ImpactofanacousticstimulusonthemotilityandbloodparametersofEuropeanseabass(DicentrarchuslabraxL.)andgiltheadseabream(Sparus aurataL.)."MarineEnvironmentalResearch69(3):136-142.

Figure 3: Noise disturbances monitored in an aquaculture on-growing tank. Waveform and spectrogram representations: A) Background sound level; B) Hand feeding commercial dry pellets of 4.5 mm two times five pellets at the time; C) Knocks against the tank wall. Three sets of three knocks caused with the bare fingers.

30 | InternAtIonAl AquAFeed | July-August 2012

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30 | InternAtIonAl AquAFeed | July-August 2012

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VOLUME 15 I S SUE 4 2 012

THE INTERNATIONAL MAGAZINE FOR THE AQUACULTURE FEED INDUSTRY

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