TurkJZool 31(2007)265-270 ©TÜB‹TAK FoodUtilisationinaLaboratoryColonyoftheGiantAfricanLand Snail,Archachatinamarginata (Swainson)(Pulmonata:Achatinidae) RosemaryI.EGONMWAN* DepartmentofZoology,UniversityofLagos,Akoka,Lagos-NIGERIA Received:28.03.2006 Abstract: Thisstudyinvestigatesfoodconsumptionbyjuvenilesandadultsoftheediblegiantlandsnail Archachatinamarginata underlaboratoryconditions.Inoneexperiment,thesnailswerefedweeklyfromhatchingfor13monthswithweighedamountsof lettuce(Lactucasativa),carrot(Daucuscarota),potato(Solanumtuberosum),apple(Maluspumila),andcalcium.Anothergroupof 2-month-oldA.marginata ovumwasfedsinglyfor3daysoneachofthetestfooditems.Theresultsshowthat,whengivenachoice, A.marginata canselectfromthe4typesoffoodandcalcium.Whengivennochoice,lettuceprovidedhighdigestibilityandusability forthejuvenile A.marginata butpotatogavethebestgrowth.Themonthlyconsumptionofcalciumincreasedastheshelllength wasincreasingrapidlyuntilmonth5,thereafterdeclininggradually,untilfrommonth8onwardsthesnailsconsumedverylittl e calciumpermonth. KeyWords: Foodutilisation,growth,laboratorycolony,landsnail, Archachatinamarginata Introduction emergencefromtheshell(Baur,1992).Juvenilesof Ingestionandassimilationareessentialphasesof Cantareusaspersus feedonmoregreenmaterialthanthe energytransportfromonetrophicleveltoanother,and adults(IglesiasandCastillejo,1999),whilein Achatina manyterrestrialgastropods,beingprimaryconsumers, achatina itisonlytheadultthateatsfruits(Hodasi, playanimportantroleinthefunctioningofecosystems 1995). (StaikouandLazaridou-Dimitriadou,1989).Itis Archachatina (Calachatina) marginata (Swainson, thereforeimportanttoperformaquantitativestudyof 1821),oneofthegiantAfricanlandsnails,isendemicto foodconsumptionandassimilationinsnailsinorderto tropicalWestAfrica.Itisrestrictedtoanareafromthe assesstheirroleinecosystemdynamics(Mason,1970; BeninRepublicinWestAfricatoZaireinCentralAfrica CharrierandDaguzan,1980;StaikouandLazaridou- (Bequaert,1950;Mead,1950)andattainsanadult Dimitriadou,1989). weightofabout700g. A.marginata iseconomically Thefoodchoicesofterrestrialgastropodsare importantbecausethespeciesisinhighdemandasa influencedbythequalitativecompositionofthefoodand proteinsourceinmanyWestAfricancountriesincluding itsquantitativeavailabilityaswellasbythenutritional Nigeria(Ajayietal.,1978),wherethemeatisaluxury needsofthegastropods(Calow,1970;VanderSteenet food.Despitethis,thespeciesisnotcultivatedona al.,1973).Thereisapositivecorrelationbetweenfood commercialleveland,asaresultofhuman-relatedimpact availabilityanditsproportioninthegastropoddiet (e.g.,deforestationandcollectionforfood(Ajayietal., (Speiser,2001),andthereforethedietislikelytovary 1978)superimposeduponlongpre-reproductivelifeand seasonallyandmayaffectreproductionandgrowth(Van lowfecundity(Egonmwan,2004),thenaturalpopulation derSteenetal.,1973;Scheerboom,1978).Dietspecific inthewildisdwindling.However,inrecentyearsthe toagehasbeenobservedinsometerrestrialgastropods commercialpotentialofthespeciesisbeinginvestigated (Baur,1992;Speiser,2001);forexample,in Arianta bymanyamateursnailfarmersandmoreattentionis arbustorum,thehatchlingsfeedontheeggshellbefore beingpaidtofarmingofthegiantsnailasopposedto theyfeedonplantmaterialsforafewdaysafter exploitationofwildpopulations.Innature A.marginata *E-mail:[email protected] 265 FoodUtilisationinaLaboratoryColonyoftheGiantAfricanLandSnail, Archachatinamarginata (Swainson)(Pulmonata:Achatinidae) feedsonboththeleavesandfruitsofagriculturaland andfreshweighedfoodwasprovided.Theexperiment wildplants(Ajayietal.,1978),andthereforethereisan wasterminatedat13months,afterthesnailsattained opportunityforamixeddiet.Therewaspoorgrowth sexualmaturity.Thedifferencesbetweentheamountsof when A.marginata wasfedonsingledietof Luffa foodingestedwerestatisticallyanalysedusingone-way officinalis,awildweed,orTalinumtriangulare,waterleaf analysisofvariance(ANOVA)(Townend,2002). (Ajayietal.1978),butsnailsfedonpawpawfruit,maize, Anothergroupof17two-month-old A.marginata andcassavagrewlarge.Artificialfooddevelopedfor (meanbodyweight5.8±0.3g)werestarvedfor5days molluscs(Standsen,1951;Wright,1973),although tocleartheirguts,weighed,andthenfedsinglyoneach promotinggoodgrowthrates,isexpensiveandspoils ofthetestfooditemsinturn.Foodwasgiventothe easilyevenat4°C(Parasharetal.,1986)andsoitwill snailsrandomlyandafter3daystheuneatenfoodand notbesuitableinWestAfrica,wheretemperaturesare faeceswereremovedanddried.Thesnailswerestarved highandstoragefacilitiesarepoor. againforanother5days,andanothertypeoffoodwas Astheexperimentswerecarriedoutformorethan12 provided,untilallthe4foodtypeswereused.Thesnails months,thisstudypresentsacomprehensivereportof wereweighedbeforeeachfoodwasprovidedandafter3 foodselectionin A.marginata rearedinthelaboratory daysoftheexperimentforeachfooditembeingtested. andtheinfluenceithasonthegrowthofthesnails. Therelationshipbetweentheamountoffoodeatenand bodyweightwasstatisticallyanalysed. MaterialsandMethods Thedryweightsofthesnailswerecalculatedusinga correctionfactorof0.27(obtainedbydryingagroupof Biologicalmaterial 17snailstoaconstantweightina60°Coven),thatis, Snailsusedintheexperimentweretheprogeny, thewatercontentofthesnailsis73%ofthewetweight. rearedinthelaboratory,ofsnailscollectedfromthefield. Dataanalysis Theyweremaintainedinatemperature-controlledroom at25°Cwithuniformilluminationandaphotoperiodof Thefollowingwerecalculatedfor A.marginata LD=12:12(thelightphasebeganat0700hours). followingthemethodsdescribedbyWaldbaueretal. (1984)andEgonmwan(1992) Choiceoffoodbythesnail Fortyhatchlingsof Archachatinamarginata were taken2dayspost-hatchingandeachwasnumberedwith 1. Approximatedigestibility(AD) Indianink.Theywereweighedindividuallyandtheshell = F–EX100 lengthwasmeasuredwithacallipertothenearest0.1 F mm.Thesnailswererearedsinglyinclearplastic containerswithmeshtopslinedwithmoisttissuepaper. 2. Theefficiencyofconversionofdigestedfoodto biomass(ECD) Everyweek,thesnailswereprovidedwithweighed G amountsoflettuce( Lactucasativa L.),carrot( Daucus = X100 F–E carotasativus (Hoffm.)Archang.),potato( Solanum tuberosum L.),apple( Maluspumila Mill.),andnatural 3. Theefficiencyofconversionofingestedfoodto chalk(calcium).Thedryweightofthefoodgiventothe biomass(ECI) snailwasobtainedbymultiplyingthewetweightofeach G foodbyafactorof0.055forlettuce,0.269forpotato, = X100 F 0.126forapple,and0.096forcarrot,obtainedby dryingaweighedamountofeachfoodinanovenat60 Theindiceswerecalculatedonadryweightbasis, °Cuntilaconstantweightwasobtained. where Attheendofeachweek,theuneatenfoodandfaecal E=dryweightoffaecalmatter matterwereremovedanddriedtoaconstantweight beforeweighing.Thesnailswereweighedandmeasured F=dryweightoffoodingested weekly.Thesnailswerethenplacedincleanlinedboxes G=dryweightgainedbysnails 266 R.I.EGONMWAN Results bymonth2(Figure1b),graduallydecliningthereafter Feedingandgrowth (withanisolatedtroughatmonth6)untilitreacheda verylowlevelfrommonth11totheendofthe Foodintakeincreasedduringthefirst5monthsoflife experiment.Thedevelopmentofanapricot-yellow uptothefirstgrowthandfeedingpeaks(Figure1).Food columellaindicatedthatthesnailsattainedsexual consumptiondroppedduringmonths6to7;thiswas maturityatmonth8,althoughnoeggswerelaidduring followedbyanotherfeedingpeakfrommonth8untilthe theperiodoftheexperiment. endofobservationatmonth13.Therateofincreasein bodyweightfluctuatedfromthebeginningofthe Foodselection experimentuntilitwasterminatedat13months(Figure Potatomadeupthegreatestpercentageoffoodeaten 1b).Themonthlyincreaseinshelllengthreacheditspeak bydryweight(44%),followedbyapple(27%)andlettuce (a) 60 Increasedfood Decreasedfood Increasedfood intake intake intake 50 40 Calcium Potato 30 Apple Carrot Lettuce 20 Dryweightoffood(g) 10 0 1234567 8910111213 25 (b) 16 bodyweight 14 20 Shelllength 12 15 10 8 10 6 Bodyweight(g) 4 Shelllength(mm) 5 2 0 0 1 23 45678 910111213 Age(Months) Figure1. a. Thetotalamountofdryfood(lettuce,carrot,appleandpotato)ingestedbyA.marginata ovum.Theobservationsstartedwhenthesnails hatched.Valuesarethemonthlymeans. b. Themean(±SE)monthlyincreaseinbodyweightandshelllengthof A.marginataovum fedonamixeddietasabove. 267 FoodUtilisationinaLaboratoryColonyoftheGiantAfricanLandSnail, Archachatinamarginata (Swainson)(Pulmonata:Achatinidae) (21%),withcarrottheleastpreferred(8%)(Figure1a). 12 (a) Therewasashiftintherelativeamountsofthedifferent 10 foodeaten,butthisshiftoccurredfrommonth7onwards, 8 6 startingbeforetheattainmentofsexualmaturityatmonth %ECD 8.Duringmonths1-6thedietwasmadeupofpotato 4 2 (49%),lettuce(24%),apple(21%),andcarrot(7%),but 0 formonths7-12therewasareductioninthepercentage 123456789101112 ofpotatoto41%andlettuceto19%,whilethepercentage ofappleincreasedto31%andthatofcarrotwaslittle 8 (b) changedat9%.Significantdifferencesintheamountsof 7 foodingestedbythesnailsweredetected(one-wayANOVA, 6 5 F =9.80,P<0.0001). 4,60 4 %ECI Themonthlyconsumptionofcalciumincreasedfrom 3 2 2ginmonth1,astheshelllengthwasincreasingrapidly 1 (peak13gatmonth5),thereafterdeclininggradually, 0 untilfrommonth8onwardsthesnailsonlyconsumed 123456789101112 between3.0and2.0gofcalciumpermonth(Figure1a). 90 (c) 80 Theassimilationefficiency(Figure2)ofthefood 70 providedfluctuated;thevalueforECDwas2%-10.2% 60 50 (Figure2a);ECIwas1.2%-7.2%(Figure2b)andADwas %AD 40 30 53%-81%(Figure2c).Inmonth7,whenthesnails 20 10 experiencedthebestgrowth(weightgained,17.5±1.5 0 g,shelllengthgained,8.0±0.6mm)butaterelatively 12345678 9101112 little(29.5g),theassimilationefficiencieswerehigh:the Age(Months) digestibilityofthefood(AD)was81±2%,assimilation Figure2. MonthlyvariationintheutilisationparametersforA.