genetic selection

7/20/2015 LectureNotesonCompositeFishCultureanditsExtensioninIndia

http://www.fao.org/docrep/field/003/ac229e/AC229E11.htm#ch11.2 1/17

Producedby:FisheriesandAquacultureDepartment

Title:LecturenotesoncompositefishcultureanditsextensioninIndia... Moredetails

GENETICSELECTIONANDCARPHYBRIDIZATIONH.A.KhanFreshwaterAquacultureResearchandTrainingCentre(CIFRI),DhauliP.O.KausalyagangViaBhubaneswar2Orissa(India)

1INTRODUCTIONThemainpurposeoffishselectionistoimprovetheexistinganddevelopnewbreedsandhybridsandthusincreasetheirproductivity.Forimprovingthequalityofcommerciallyimportantfishspecies,theuseismadeoftheirvariationinmanymorphological,physiologicalandbiochemicalfeatures.Amarkedproprotionofthisvariationishereditary,thelevelofwhichisveryhighinfishpopulationandhelpsinfishselectionwork.

Incomparisontothebreedingofdomesticanimalsfishcultureisayoungscience.FishcultureinChinaandIndiahasbeeninvoguesincelong.Butthedomesticationoffishandcreationofbreedsdifferingfromtheirwildparentsinhigherproductivitytraitswasactuallystartedonlyafewcenturiesago.Withthenotableexceptionofgoldfish,ornamentalcarpandperhapsthecommoncarp,fewfishcouldbeconsidereddomesticatedeventhoughsomestrainsoftrout,forexample,aremuchmoreadaptedtohatcheryconditionsthantheirwildcounterparts.OtherspeciesliketheChinesecarps,Indiancarps,Tilapiasp.andChannelcatfisharebecomingdomesticated.

Ofallculturablecarps,onlycommoncarphasbeenbredforsufficientlylongtimeanddistinctbreedsofthisspeciesthroughselectiondevelopedare:InUSSRtheUkrainiancarp,Ropshacarp,hybridsofthefirstgenerationofthedomesticatedcarpandtheAmurWildcarp,theNivchancarp,theCentralRussiancarp,theKazakhistancarp,theKasnodarcarp,theByelorussianbreedandtheParrabreedofcarp(Kirpichnikov,1981)inIsraelDor70carp(Wohlfarth,Lahman&Hulata,1980)andinHungarytheHungarianstrain(Bakos,1979).

2METHODSOFFISHSELECTION

2.1Massorindividualselection

Thetermmassofindividualselectionisusedtodescribeartificialselectionanduseinsubsequentreproductionofindividualshavingthebestphenotypes.Thetraitsusedinsuchaselectiondependonspecificpurposeandmayincludeincreasedweightorbodysize,goodexteriorindices,rateofsexualmaturation,thenecessarypigmentation,thedesignpatternofscaling,resistancetounfavourableenvironmentalconditionsandtodiseasesandcertainimprovedphysiologicalorbiochemicalcharacteristicseasilymeasurableinfishes.Selectionmayincludeinteriorfeaturessuchasnumberofintramuscularbones,sizeofairbladder,etc.

Theefficiencyofmassselectionisexpressedbysimpleequation(Falconer,1960).



R = ih2=Sh2(1)Where

R = hereditaryimprovementofcharacterofonegenerationS = Selectivedifferential(differencebetweenmeanforselectedindividualsandinitialpopulationmean)

i = intensityofselectioni.e.selectivedifferentialexpressedinmeansquaredeviationsh2 = heritabilityofcharacter = variabilityofinitialpopulationexpressedintermsofstandarddeviation.

Nowletusconsiderthepossibilityofincreasingeachofthetermsintherightpartoftheaboveequation,whileperformingtheselectionofafish.

2.1.1Theintensityofselection

Theintensityofselectionmaybequitesubstantialinthosespecieswhichareveryfertile.Insuchcasewecanchooseasmallpartofagrownpopulationforbreedingandrestcanberejected.Thenumberofbestspecimensleftforbreedingiscalledtheselectionseveritycoefficient(V)

WhereN=initialnumberofindividualsn=numberofselectedindividuals

Selectionseveritycoefficientinveryfertilefishlikecommoncarpcanbeeasilybroughtto1%(1:100)oreven0.1(1:1000).OccasionallyinselectingRopshacarpinfirstyear,stillmorerigidnormsofrejection,keepingforbreedingpurposeonly0.050.02%ofthepopulation(1:2000to1:5000)havebeenfollowed(Kirpichnikov,1967).Suchanincreaseintheselectionseverityrequiresaverylargenumberofpopulationstobecultured.Theseverityandintensityofselectionarefunctionallycorrelated(Fig.I).AtlowvaluesofV(0.01orless)anyfurtherdecreaseinthosecharacteristicshardlyhasanyeffectonthevalueofselectionintensityanddoesnotcompensatefortheexpenditurenecessarytogrowalargenumberoffishespriortothetimeofselection.Ifthefertilityoffishislow,selectionwithratio1:20(V=5%)wouldbepermissible.Afurtherreductioninseverityisundesirableasitwouldbefollowedbyasuddendropofthevaluei.Withtheincreasedsizeofinitialpopulationandthereforeenhancedimaybeaccompaniedbyreductioninheritability(h2).Ithasbeenobservedbymanyinvestigatorsthatinyoungstagesofcommoncarp,whengrown,underconditionofhighdensity,theweightdistributioncurvebecomesmarkedlyasymetricafewshootfryalsocalledjumpersorchampionsappearwhoserateofgrowthgreatlysurpassesthatoftheircompanionsofthesameagethefoodcompetitionbeingthemeanreasonforthissizedifference(Wohlfarth,1977).Inpresenceoffoodcompetition,anincreaseinseverityandintensityofselectionaboveacertainlimitwillhaveabadeffect.

2.1.2Variabilityofinitialpopulation

Thevariabilityofinitialpopulation()mustbesufficientlyhighifVisnearzero,evenwithaveryhighintensityofselectionandconsiderableheritability(about0.60.8)theefficiencyofselectionmayturnouttobelow.Inmassselection,onlygeneticvariationisimportantbecauseanyincreaseinthevalueofnonheriditaryvariablesduetotheincreaseinenvironmentalvariationismeaninglessbecauseitwillresultinaproportionaldecreaseinheritabilityandwillnotenhancetheefficiencyoftheselection.

2.1.3Heritability

Heritability,inbroadsense,istherelationbetweenthewholegeneticvarianceandtotalvariance:



Totalvariance,inturn,expandsintoanumberofcomponents.

WhereEisenvironmentalvarianceandjisvarianceofinteractionbetweenenvironmentandgenotype.TheE2andj2shouldbereducedandthiscanbedonebycreatingsimilarhomogenousconditionsforgrowing(tobeginwithparentmaintenanceconditions)andreducingfoodcompetitionwhichfrequentlyenhancestheinteractionalvariance.

Heritabilitycanbeincreasedinmanyways:

i. Bycrossingunrelatedindividuals,includingcrossingbetweenlines,breedingstocks,varieties,subspeciesandoccasionallyspecies

ii. Bythemethodofunifyingfishgrowingconditionstoselection.

Infishculture,theparatypicvariancecanbegreatlyreducedbyadoptingthefollowingmeasures,theimportantonesare:

i. settingupofsimilarconditionsforallparentspriortoreproduction,ii. simultaneousperformanceofallcrossesdesignedtoyieldmaterialforselection,iii. maximalstanderdisationofenvirenmentalconditionsthroughouttheperiodoffishculture,iv. stockingoffishessimultaneouslyintopondsatamoderatedensityinordertoavoid

excessivefoodcompetition,v. measurestopreventmixingofindividualsculturedindifferentponds,vi. selectiontobeconductedattheagemaximallycorrespondingtothemarketingage.

However,inspiteofobservingallabovementionedconditions,theenvironmentalvariance(E2)incommoncarpandinseveralotherfishesprovestobeveryconsiderable.Acompleteeliminationofcausesthatproduceunequalconditionsoflifeforindividualslivingtogetherinpondsisimpossible.

Theinteractionbetweenthegenotypeandageinfishisnotveryimportantbuteventhenitexists.Theearlyphasesoflifeoffisharegreatlyinfluencedbymaternaleffect.Theenvironmentalcomponentoftotalvarianceofweightisparticularlyhighatthebeginning,butdecreasesthereafterandheritabilityofweightandsizeincreasesbyafactorof23.Geneticdifferencesaremoredetectableatlaterstagethanduringtheearlyphasesoflife.Atlaterstagefishgrowthis,however,greatlyaffectedbytherateofgonadalmaturation,sowhenselectionisaimedatweight,itshouldbedoneatthemiddleage.

Occasionally,heritabilitydecreasesbecauseofheterozygousbalance,aphenomenonpeculiartomanyspeciesofanimalsandplants.Duetogreatnumberofchromosomesincommoncarp(2n=104)andmanyotherfoodfishtheprobabilityofheterozygousbalancebeingestablishedinapopulationappearstobegreat.Hence,itistheindividualswithmaximumheterozygosisthatwillbethemostviableandfastgrowinginapopulation.

Selectionundersuchconditionsverysoonbecomesinefficient,sincethegeneticvariabilityprovestobeinthemainnonadditive.Astovariabilityofanycharacter,itistheproportionofadditivegeneticvariabilityinthetotalvariabilityofthegivencharacter.

whereA2=G2D2E2(6)

Withoutbalancedheterogygosis,thevarianceofdominanceandepistasis(D2and2)aresmallandinitiallytheadditivegeneticvariancedoesnotdiffermuchfromthetotalvariance(G2).If



thereissubstantialheterozygousbalanceformanypolygenes,thedifferencebetweenh12andh22willbeverygreat.Atrueheritabilityinspiteofconsiderablegeneticvariability(G2)willbenearzero,sincethevariabilityisnotadditive.

Itisdifficulttostriveagainstanestablishedheterozygousbalanceastheequilibriumofgenotypeprovestobeverystable.Theonlywaytocorrect,thesituationistoperformnew,sufficientlyremotecrossingswhichmaydestroythepolygenesystemandtherebycontributetoanincreaseinheritability.Table1showsthephenotypicandgeneticparametersforquantitativecharactersincommoncarp.

Table1.Phenotypicandgeneticparametersforquantitativecharacterincommoncarp(=mean,standarddeviation),CV=CoefficientofVariation,S.E.=Standarderror,Heritability(h2)asestimatedfromsire(S),dam(D)andfamily(F)Componentsorvariation

Traits CV h2sS.E. h2DS.E Nooffamilies Authorsh2fS.E

Weightoffingerlings 0.100.20 Kirpichnikov(1972)Bodyweight 0.25 Smisek(1979)Drymatter 0.150.18 doFatcontent 0.140.15 doNindrymatter 0.150.17 do4monthwt.(g) 71 17 23 0.48F 9F Nagyetal 0.12F 9F (1980)Tolerancetohypoxia 179 50 28 0.15F 9F doWeightgain(g) 366 81 22 0.47(b) 17off/parents Brodyetal.(1981)

Fromtheabovetableitisevidentthatweightheritabilityincommoncarpforjuvenilesisratherlowandthatforbodyweightofadultsisofmediumsizeandhigherforyounganimals.Selectionforweightisalwayspossible,butitdoesnotalwaysgivethedesiredresults.Inthepresenceoffoodcompetition,moreaggressiveindividuals,whoareabletosnatchfoodfromothersinthepond(Moav&Wohlfarth,1967)maynotnecessarilybethebestatassimilatingfood.Itisevidentthatforimprovingtherateofgrowthmassselectionshouldbecombinedwithtestingforrelatives.

Massselectionshouldbereplacedbytestingforrelativesonlyincaseswhensuchcharacteristicsasfatcontent,biochemicalcompositionofmeatanddegreeofboninessaretobeknown,oriftheprincipaltaskistoraisethefishproductionofponds.

2.2TheSelectionforRelatives

Theselectionforrelativesinvolvestoagreatextenttheselectionforgenotypesthepositivecharacteristicsofindividualschosenforsubsequentreproductionareknownfromananalysisoftheircloserelatives.Therearetwoformsofselectionforrelatives:(a)familyselectionand(b)evaluationofspawnersbyprogenytesting.Asinmassselection,theefficiencyofselectionforrelativeisexpressedbyasimpleequation.

R=if.fhf2(7)

Inthisequationintensityofselection(if)equalsthedifferencebetweenmeanforselectedfamilyandpopulationmeanexpressedinmeansquaredeviations,ofcharacterisesthevariabilityoffamilymeansandh2showsheritabilityofdifferencesbetweenfamilyeans.Infamilyselectionthevaluefandselectionintensityarereducedthanthesevaluesinmassselection,buttheheritabilitymeanscanreachveryhighvaluesifthefamilitiesaregrowntogetherundersimilarconditions.

2.2.1Familyselection

Familyselectionisgenerallyusedwhenhereditaryofselectedcharacteristicislow.Thisrequires



farmingofseveralfamiliesoroffspringsfromdifferentpairsorsmallpotentialgroupsunderoptimumconditions.Thememberofcrossingsmaybe810orwhenculturefacilitiesexist,itmaybeashighas15or20.

Theselectionintensity(f)dependstoaverygreatextent,onthenumberoffamilies.Thevariabilityofthefamilymeans(f)isnotgreatandcanbeincreasedonlyattheexpenditureofenlargingitsgeneticcomponent.Theheritabilityofmeans(hf2)isincreasedanditapproacheswhenallfamiliesarekeptunderstandardconditions.Themostimportantconditionsforfamilyselectionare:

i. Sufficientgeneticvariabilityoffamilymeanii. Homogenityofconditionsforgrowingseparatefamiliesorsufficientreplicatesof

experiments.

2.2.2Progenytesting

Thesimplestmethodinvolvescomparisonofoffspringsobtainedfromdifferentpairsornestsofparents(Fig.2a)inthiscasetheevaluationreferstothecombinationofindividuals.Inthesimplifieddiallelecrosses(Fig.2b)whicharegenerallypractised,malesorfemalesareseparatelycrossedwithoneormoreindividualsoftheoppositesex.Thematuringofeachofthemalestestedwithtwofemalesprovidesasufficientlyreliableevaluationofthebreedingqualitiesofthesemales.Acompletediallelecross(22,33,55,1010,etc.)alsoenablesthefishbreedertoselectthebestindividualsbelongingtoothersex,sincethenumberofoffspringincreasesitsproportiontobesquarenumberofparentsofonesexsubjectedtoexamination(Fig.2c),onehastofacetheproblemofgrowinglargenumberofoffspringsunderuniformstandardconditions.Theprogenytestingisalsotimeconsumingandrequiresoneortwoyears.

TestingofspawnersofeithersexofcommoncarphasbeendoneforselectioninUSSR(Kirpichnikov,1966)andinIsrael(Moav&Wohlfarth,1967)thatabout70%ofthedifferencesbetweenprogenymeanscanbeattributedtogeneticvariance.Thusprogenytestsprovideaneffectivetoolforidentifyinggeneticallysuperiorprogeniesandparentalgroups.Theconditionsandrequirementsforprogenytestingaresimilartothoseusedinfamilyselection.

2.3CombinedSelection

ComparisionoftheequationR=Sh2andRf=Sf,h2fallowsonetodeterminewhichoftheselectionmethodsisbetterforfishbreeding,ifSh2>Sf,h2fthenmassselectionistobepreferredoverfamilyselectionorviceversa.Selectionforrelativeswillbemoreeffectivefortraitswithverylowheritabilityi.e.lessthan0.5andwhenh2ishigherthan0.5,massselectionismoreefficientthanthefamilyselection.Whenh2=0.5,familyandindividualselectionareofequalefficiency(Falconer,1960).Withfish,selectionshouldbebasedonacombinationofmassandfamilyselection.Massselectionisonlyofinterestwhengrowthrateistheonlytraitofeconomicimportanceandishighlyheritable(Gjedrem,1963).Theresponseofcombinedselectionistheoreticallyequaltothesumtotalresponseofeachoftheselectionmethodsused.

Rs=Rf+Rm+Rpr,whereRf,RmRPrrefertotheeffectivenessoffamilyselection,massselectionandprogenyselection.

Thefirststepincombinedselectionconsistsofcrossesbetweenheterogenousunrelatedparents,suchcrossesareaimedatobtainingasmallnumberofprogenyupto10incommoncarpbreeding.Duringthecultivationofthesefamiliestheirreproductivepropertiesareevaluated.Thesepropertiesincludeviability,growthrate,thequalityofflesh,etc.sothatbestfamiliescanbeselected.Thesecondstageincludesmassselectioninseveralofthebestfamilies.Atthethirdstageparentsareexamined,usingprogenytestingParentsofjustonesexwheretheonsetofmaturityoccursearlieraretested(malesincommoncarpbreeding).Thistestingistobecompletedbythetimeofonsetofmaturityofindividualsoftheothersex.

3NEWTRENDSINFISHSELECTION



3.1Applicationofgeneticmarkerinfishselection.

Theinformationregardingthepatternofinheritanceofmorphological(bothquantitativeandqualitative),physiologicalandbiochemicaltraits,particularlythoserelatedtoyieldcapacitycanbedirectlyutilizedinplanningselectionwork.Thelaterinformationhelpsindecidingwhethertogoformassselectionorselectionofrelativesandisusefulindevelopingasystemofcrosses.AgoodexampleofsuchanapplicationoftheinformationcanbeseeninthepurificationofthebroodstockoftheRopshacommoncarpfromtherecessivegene.

InthestudyonhomoandhetorozygosityinthescaledcarpinthegeneS,(mirrorandscatteredscale),thebackcrossingiscarriedoutthus:

1) S(S?) nnssnn scaled scattered2) S(s?) nnSsnn scaled scaledheterozygous

Intheformercase,thescaledandscatteredoffspringoftheheterozygousparentsareproducedina1:1ratio.Inthelattercase,theratiois3:1(threescaledperonescattered).Theentireoffspringofhomozygousscaledparentsinanyofthetwocrossingshaveacompletelyscaledintegument.From1956to1964,469parentsofRopshacarpwereexaminedbythistechnique,247werehomozygous.Thisworkenabledcompleteeliminationoftheoccurrenceofthescatteredcarpasearlyasinthe5thselectedgeneration(Kirpichnikov,1971).

Useofgenesformarkingthebreedingstocksisanotherimportantpromisingtrendandpresentlygeneticmarkershavebeensuccessfullyusedforlabellingdifferentstocksofcommoncarpe.g.,selectionofCentralRussiancarpincludingthebreedingoftwostocksdifferingintheS(patternofscale)andD(pigmentationofspinesandhead)loci(Kirpichnikov,1981)andtwostrainsofcommoncarpinIsraelmarkedwithcolourrecessivegene(MoavandWohlfarth,1967).Genemarkersarehelpfulinestablishingtheoriginofcertainfishbreeds.Ifthecorrelationbetweenmarkergenesandselectivetraitissignificant,theselectioninvolvingsuchmarkersmaybeconsiderablyaccelerated.

3.2Artificialgynogenesis

Gynogenesisisaspecialtypeofsexualreproductionrequiringinseminationwhennucleusofsperm,whichhaspenetratedtheovum,undergoesinactivationintheeggplasmanddevelopmentofembryoiscontrolledexclusivelybymaternalnucleus.Thechromosomesofspermsareeliminatedsoonafterfertilization.Thetechniqueofartificialgynogenesisisbasedoninactivationofspermbyirradiationanddiploidizationofthefemalechromosomesetbyacoldshock.ThismethodhasbeenemployedsuccessfullyonCyprinuscarpio(Golovinskaya,1968)andintwoIndianmajorcarpsviz.,CatlacatlaandLabeorohita(GeorgeJohnetal.,1984).Alsotheproductionofmonosexbroodsforpopulationcontrolhasbeenattemptedwithgrasscarp.

Thegreatadvantageofthistechniqueisthatitconstitutesadefactovegetativereproductionthatcanmaintainandmultiplyasinglesuperiorgenotyperegardlessofitslevelofheterozygosity.Anotheradvantageisthatgynogeneticallyreproducingpopulationstendtohaveonlythefemalesex.Thisprovidesmeansofselectingfemaleswithhighergenetictendencyforgynogenesis.

3.3Polyploidy

Infishesnaturalgynogenesisisintimatelyassociatedwiththephenomenonofhybridization,apomxisandpolyploidy.Triploidamieoticparthenogenesisandrogenesismayoccurasaresultofbackcrossesofparthenogeneticdiploidfemaleswithmalesofrelatedbisexualspecies.Incaseofthecrossbetweentriploidgynogeneticfemaleswithdiploidmales,tetraploidgynogeneticindividualsmaydevelop.Triploidshavebeenproducedbycoldshocktreatmentofthefertilizedeggsofcommoncarp(Garvaietal.,1980).Thesefishesareexpectedtobesterile.Theinteggenerichybridsbetweengrasscarpandeithercommoncarporbigheadcarpappeartobelargelytriploid(AllenandStanley,1981).ThepopulationofCarassiusauratusglibelioinJapan



hasbeenreportedtocontaintetraploids.

4CROSSINGASAMETHODOFINCREASINGTHEHETEROGENITYOFTHESELECTIONMATERIAL

Theselectionresponsedoes,toalargeextent,dependonthelevelofheterogenityoftheselectedgroups.Crossesbetweenunrelatedindividualsenrichthestrainincreasingthegeneticcomponentoftheirveriationandtherebyfacilitatingselection.Anotherresultisthedisappearanceofanyharmfuleffectofinbreeding.Crossingalsoensuresthepreservationandperfectionofthereproductivequalitiesofthebreedandallowsheterosistobeutilizedtoitsutmostineverygeneration.Crossinghelpsinimprovingthebreedingqualityofthelocalbreedbymakinguseofthefewvaluabletraitsofanotherbeed(improver)andinincreasingtheviabilityofthebreedbyintroducinggenesresponsiblefortheresistancetoenvironmentalfactorsanddiseases.Inaccordancewiththeaboveobjectives,followingtheoriginalcrossing,thereproduction,ofthehybrid,populationiscarriedoutbymeansofthereproductive,introductory,absorptiveoralternatecrossing.

4.1Thereproductivecross(Fig.3a)

Thisisusedwhenmanyusefultraitsaretobecombinedfrombothcrossbreedsorspecies.Thisiseasilyachievedwhenhybridsarecompletelyfertilebutrequirethoroughselectioninallhybridgenerations.Examplesofsuchcrossesare:TheUkrainianandRopshacommoncarpbreeds,theHungariancarp,etc.

4.2Theintroductorycross(Fig.3b):

Thisisusedwhenitisrequiredtointroduceoneorseveralvaluabletraitsofanotherstrainorspeciesintothelocalhighlyproductivebreed.F1hybridsoftwoformsarethenbackcrossedmanytimeswithindividualsofthelocalbreed,whoseimprovementsintended.Inthisprocess,thebackcrosshybridspossessingthedesiredtraitsofdonorstrainareusedforsubsequentreproductiontoimprovethebreed.Ifthesetraitsaredeterminedbydominantclearlymanifestedgenes,theproblemofconservationofrequiredcharacterscanbesolvedrelativelyeasily,otherwiseincaseofrecessivegenesorwheninheritanceispolygenic,theriskoflossofcharactersisveryhigh.

4.3Theabsorbingcross(Fig.3c)

Similartointroductorycross.Aseriesofbackcrossesiscompletedaftertheinitialcrossoftwostrainsbuthybridsarerepeatedlycrossedwiththeindividualsofstrainsusedforimprovementandnotoflocalstrain.Strictmeasuresshouldbeadoptedaimingatconservingthemostusefultraitsofabsorbedstrains,inthiscasethelocalone.

4.4Thealternativecrosses(Fig.3d)

Thisrequiresintermittentcrossingofhybridswiththeindividualsbelongingtothetwoinitialbreedsasfollowedbyselectionofthenecessarycombinationoftraits.After3or4generations,thealternatecrossisreplacedbyreproducingone,otherwise,itisdifficulttostabilizethetraitsofthenewhybridbreed.

4.5Hybridization

F1hybridsiftheypossessheterosiscanbeculturedcommercially(Moav&Wohlfarth,1967).Heterosisappearstodependontwomaincompensatorymechanisms.Thecombinationofusefuldominantgenesaccumulatedbybothcrossedformsinhybrids(hypothesisordominance)andtheincreaseinhybridsofthetotallevelofheterozygosity(thehypothesisofoverdominance).Anincreaseinthebiochemicalversalityinhybridsoccursinbothcases.Heterosisinnaturalpopulationisgenerallymanifestedasariseinthefitnessofhybridsintheelevationoftheadaptive



value.Thisistypicalofmanyintraspecificandcertaininterspecificfishcrosses.Maximalcareisrequiredincarryingoutcommercialhybridization,becauseifF1hybridsareleftinthewaterbodies,therearechancesofcontaminationofthebroodstockoftheinitialforms.Thisleadstothedeteriorationoftheeconomicallyimportantstrains.Anexampleofsuchhybridizationcanbecitedincaseofdomesticcommoncarp,withitslivingancestor,thewildcarp.Bettercontrolofcommercialhybridizationcanbeconsideredbytheuseofgeneticmarkers,bothparentsandhybridsmaydifferintheallelesofthegenesresponsibleforthecolourpattern,scalepatternandcertainbiochemicalloci.Somepromisingimportanthybridcombinationsare:(1)InterbreedhybridsofcommoncarpcrossesbetweenRopshaand'Ukrainiancarps,ofthescaledandformed,Ukrainiancarps,threestocksoftheKrasnodarcarp.HeterosismanifestedinbettersurvivalandproductivityhasbeenobservedinthecrossesofHungarianandPolishcarps,andcrossesoftheJapaneseYamatocarpwithEuropeanmirrorcarp.(2)IntraspecifichybridsofsilvercarpofAmurandChineseorigin(3)HybridsofdomesticcarpandAmurwildcarp(Cyprinuscarpiohaemalopterus)(4)Intergenerichybridsofcommoncarpandcruciancarp(5)Intergenerichybridsofsilvercarpandbighead(6)IntergenerichybridsofCatlacatlaandLabeorohita(Chaudhuri,1971)andmanyothersspeciesasshowninTable2

5BREEDINGSYSTEMSADOPTEDFORFISHSELECTIONINSOMECOUNTRIES

Inordertoutilizecompletelytheadvantagesassociatedwithheterogenouscrossings,fishbreedingshouldbecarriedoutaccordingtoadefiniteplan,dependingontheknowledgeofgenetics,inbreddepressionandheterosisinfishcrossing.Inmakingcrosses,inducedbreedingofthespeciesfollowedbyartificialfecundationisemployed.Alsoforcarryingoutgeneticexperimentationonlargescale,anadequatemethodofmarkingfishforindividualorgroupobservationsistobedeveloped.Thebestresultshavebeenobtainedinmarkingexperimentalfishbyfinclippingorbrandmarking(Moavetal.,1960)orsubcutaneousinjectionsoforganicdyes(dichlorotriazineandothercompounds)(ZonovaandKirpichnikov,1971)orbyinjectingblue,redoryellowflurescentgranulesintothespine(Smithermanetal.,1983).UnderIndianconditions,commoncarpwhoninjectedwithProcianMbluestainbytheauthorhasretainedmarksforlasttenmonthsandstillthemarksarequitedistinct.

Thevariousfishbreedingsystemsfollowedforthegeneticimprovementofcommoncarpindifferentcountriesaredescribedasfollows:

USSR:ThemethodofparallelbreedingoftwoormoregroupsisusedfortheselectionofRopshacarp(Kirpichnikov,19711971).Inthissystemtwoorthreegroupsareconcurrentlychosenwithinabreed,withoutintermingling,allowinginsideeachamoderateinbreedingandcarryingoutselectionineachgeneration.Forcommercialpurposesfishfromdifferentgroupsarecrossedtoavoidcloseinbreeding(Fig.4).

Israel:

(a)Breedingingroupswithfamilyselection:

Eachyearabout20pairsofcommoncarparespawnedandprogenytested.Thetestedpairsmayincludethesethatexcelledinpreviousyears.Theymayalsoincludeagroupoffullsibsofasuperiorprogenyofthepreviousyearmassspawnedwithanunrelatedmale.Thefastergrowingindividualsofthebestprogeniesareselectedtoserveasparentsofcrossbreedfry.Theremainingprogeniesarecullod.Thesameprocessisrepeatedwithnewpairseachyear(Moav&Wohlfarth,1967).

Asthenumberoftestedcombinationincreases,thepossibilityoffindinganew,bestcombinationbecomessmallandfurtherimprovementrequiresselectionforcombiningabilitywithinthebestparentalline.Thisrequirementismetintherecurrentselection(RS)andreciprocalrecurrentselection(RRS).Thebasicfeatureoftheaboveselectionproceduresthatdifferentiatesthemfromotherselectionprocedureisthatthepurebredparentsareselectedonthebasisoftheperformanceoftheircrossbredhalfsibsratherthanonthebasisoftheirownperformance(Fig.6).

(b)Opengenepoolsystem:



RRSmethodoranyotherbasedonfamilyselectionorprogenytestingisthatitincreases,inbreedingintheparentlines.Toavoidthis,theuseofopengenepoolsystemmaybemade.Thissysteminvolvesthemaintenanceofgeneticallymarkedreservegenepoolsforeachoneofthetwoparentallines.Eachcycleofprogenytestingmayincludeasmallproportionoftheindividualsfromthereservegenepools.

Iftheprogenytestingresultsshowthatoneormoreofthegenepoolimmigrantsproducedsuperiorcrossbredprogeny,purebredprogenymaybeincorporatedintothepurebredparentalline.Selectionshouldaimatanincreaseincombiningcapacity(Moav&Wohlfarth,1967).ThismethodhasalsobeenfollowedandextensivelyusedbySovietfishbreeders(Golovinskaya,1971).

Hungary:

TheHungarianlandracesofcommoncarpwereusedforgeneticcrossing.Ineachcrossonlyonemaleandonefemalewereused.Thecarpspawnerswereidentifiedbyburnsorbrands,boaringlineandindividualmarks.Theprogenypopulations,weredifferentiatedbycollectivemarks,eachgroupreceivingabrandedstrip2cmlongondifferentpartsoftheirbody.Inplanningcrossingcombinationthefollowingaspectsweretakenintoconsideration(Fig.5).

i. Matingoutstandingfemalesandmalespossessingthesamevalueofstabilizedandfurtherimprovementofadvantageouscharacters.

ii. Matingofanoutstandingmaleandfemalehavingtwodifferentcharactersforthecombinationofadvantageousfeatures.

iii. Matingofonefemalewithoutstandingcharactersandmoremalesforthecontrolofcombiningabilityandfortheselectionofmostsuitablelineofmales.

iv. Matingofrelatedindividualswithinpurelinesfortheproductionofinbredlines.

Theproductivecapacityofcarphybridswasestablishedbytheevaluationofeggfertility,percentageofsurvivalinthefirstandsecondyearsoflife,increaseinweightduringthesecondyear,foodconversionability,percentageofconsumablefleshandfatcontentofflesh(Bakos,1979).

6CONCLUSIONSi. Theefficiencyofmassselectioncanbeenhancedbyincreasingtothepossibleextent,the

valueofthreefactors:intensityofselection,variabilityandheritabilityofthetraittobeselected.Ofthese,increaseinheritabilityisthemostimportant,whichcanbedonebymeansofcrossing,creationofuniformconditionsforfishrearingandcarryingoutselectionattheagetobeimproved.

ii. Familyselectionandprogenytestingincarpbreedingprovetobemoreefficientthanmassselectiononlywhentheheritabilityofthecharacter(h20.10.15).Themaindifficultyinperformingselectionforrelativesistherequirementoflargenumberofpondsforgrowingasufficientlylargenumberoffamiliesunderidenticalconditions.

iii. Muchbenefitmaybeexpectedfromcombinedselectioninthecourseofwhich,massselection,progenytestingoffemales,andfamilyselectionareperformedsuccessivelyinonegeneration.

iv. Newtrendsinfishselectionsuchasuseofgeneticmarkers,artificialgynogenesisandpolyploidyhavebeendescribed.InIndianmajorcarps,viz.CatlacatlaandLabeorohita,thegynogenesishasbeensuccessfullycarriedoutforthefirsttime.

v. Methodsofincreasingtheheterogenityoftheselectionmaterialandbreedingsystems,aspractisedinUSSR,IsraelandHungary,havebeendescribed.

7REFERENCES

Alikunhi,K.H.&H.Chaudhuri,(1959)Preliminaryobservationsonhybridizationofcommoncarp(Cyprinuscarpio)withIndiancarps.Proc.IndianSci.Congr.,(3):46.



Allen,S.K.andJ.G.Stanley,(1981)Polyploidyandgynogenesisinthecultureoffishandshellfish.Int.Counc.Explot.Sea.F.,28:18pp.

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Table2:ShowingimportanthybridsofIndianmajorcarpsandChinesecarpsproducedinIndia

Femaleparentspecies Maleparentspecies Hybrid Importantcharacteristics Authority

1 Interspecifichybrids Labeocalbasu

Labeorohita Calbasurohu Attainedfullmaturityin2yearsF2generationproduced.Varyingcharactersintermediatebetweencalbasuandrohu.

Chaudhuri(1959&1971)

L.rohita L.calbasu rohucalbasu Inbothhybridsover94%fertilisationwasobtained,theirgrowthratewasfarsuperiortotheparentLabeocalbasu.

Do

2 Intergenerichybrids Cirrhinusmrigala

L.rohita mrigalrohu Relativelysmallhead,deeperbodyslendercaudalpeduncle.D2/1314P18V9A2/6C19,L.l.4647Lengthofhead5.21ofcaudal4.66heightofbody4.57intotallength,pharyngealteeth542.Fullmaturityin2years.Intermediatebodycharacters.

NaseamHamza(1971)



Labeorohita C.mrigala rohumrigal Intermediatebodycharactersascomparedtothoseofparents.Attainsmaturityin2years.

Chaudhuri(1959&1971)

Labeorohita C.mrigala rohucatla Bodycharacteristicsintermediatetoparentspecies.Colourationlikecatla,smallhead,mouthterminal,finraysresemblingthoseofrohu.Broadbodyofcatla,smallheadofrohuandmoreflesh(54%)thaneitheroftheparents.viz.,rohu(48%)&catla(45%).Fastergrowththanrohu.Fullmaturityattainedin3years.Fecunditylessthanbothparentalspecies.F2generationproduced.Slightlybettergrowthratethanthehybridcatlaxrohu.

Bhowmicketal(1981)

ReddyandVerhese(1980).

Catlacatla Labeorohita Catlarohu Greaterbodygirthandfastergrowththanrohu,smallerheadthancatlaandmorefleshthanboththeparents.Primarilyplanktonfeederbutacceptartificialfeed.Growthslightlyfasterthanrohubutslowerthancatla.F1hybridsmaturedin2years.F2generationproduced.ReddyandVenghese(1980)reportedgrowthofhybridmuchslowerthancatlaandslightlylowerthanthatofrohu.

Chaudhuri(1971)

Reddy&Verghese(1980)

Catlacatla L.calbasu Catlacalbasu

Fastergrowthratethancalbasu,smallerheadthancatlaandbodygirthmorethancalbasu.

Chaudhuri(1971)

L.calbasu C.catla Calbasucatla

Fastergrowththancalbasu. do

C.catla L.fimbriatus Catlafimbriatus

FastergrowththanfimbriatusHeadsmallerthancatlaandbodygirthnearertocatla.

do

C.idella Hypophthalmichthysmolitrix

grasscarpsilvercarp

Resembledgrasscarp,irregularlargesizedscalesatsomeplacesalongthelaterallineinsomecasesactivelarvicidalandweedicidaltendenciesinfrystage.Malesmaturedin2yearsandfemalesin3years.

Barrackpore(1980)

H.molitrix C.idella grasscarpsilvercarp

Roundbodyofgrasscarpwithsmallerscales.Mouthwithlowerlipprotrudingasinsilvercarp.Gillrakersnumerousbutnotfusedasinsilvercarp.Anaverage

Singh&Chakraborti(1970)



sizeof366mm/475ginoneyear.Didnotmature.Nonacceptanceofweeds.

Labeorohita Cyprinuscarpio rohucommoncarp

Elongateddorsalfinlikeparentspecies,butothercharacteristicsintermediatebetweenparentspecies,Sterile.Survivedforseveralmonths.

AlikunhiandChaudhuri(1959)

C.mrigala C.carpio mrigalcommoncarp

Survivalforseveralmonths Chaudhuri(1971)

Catlacatla H.molitrix catlasilvercarp

Bodygirthcomparabletocatla,sizeofheadandscalesnearertosilvercarpandcolourationslategreyondorsalsideandsilveryontoabdomen

Ibrahimetal(1980)

H.molitrix Catlacatla silvercarpcatla

Asinglespecimen,survivedfor21monthsandattained497mm/1.45kg.Showedroughnessofpectoralfin.

Barrackpore(1979)

Cyprinuscarnio

L.rohita commoncarprohu

Bodycharactersintermediatebetweenbothparentspecies.Bodyprofilenearertorohu.

Khanetal(1984)unpublished.

Fig.1RelationbetweenselectionseverityandSelectiveintensity(,1967)NSizeofpopulation



requiredforselectinganindividualVselectionseverity(%)iselectionintensity

Fig2Progenytestinginfishbreeding

Fig3TypesofCrossings



Fig.4.SchemeofcreatingbreedingstockofRapshahybridcarp(kirpichnikov,1967)CCculturedmirrorcarp,AWCWildCarp.HN+HKHybridsofNovogarad+KurskstrainsHB,HC,HJhybridsofbackcross,CrissCross(withlinear)andintermediatestrains.DoubleframsoutlinesheterosisCombinations?denotesuncontrolledcrossingduringthewar194144.



Fig5.SchemeofproductionofCommoncarphybridsshowingtheprocessofbreeding(Bakos1979)

Fig.6.Schematicpresentationofacombinationofselection(offemalesoftheparentlineA)plusmoreselectionwithinthepureline(I1,andI2representtwotestedimmigrantsoftheopengenepooloftheparentlineA)(Moav&Wholfarth,1967)

genetic selection

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