Effect of stocking densities and feed supplements on the growth performance of tilapia (Oreochromis spp.) raised in ponds and in the paddy field

摘要

TwoexperimentswereconductedatCelAgrid,KandalProvinceforaperiodof80days.Inexperiment1,12pondseachwithareaof10m2wereusedtocomparefourtreatmentsarrangedina2x2factorialwithacompletelyrandomizeddesignwith3replicates.Thefirstfactorwasfertilizerwitheffluentandnoeffluent;thesecondfactorwasstockingdensityof3or5fishperm2.Thefishineachpondwereprovidedwithfeedat5%ofthefishbiomass(DMbasis).Thefeedcontained25%ofwaterspinach,25%ofduckweedand50%ofricebran(DMbasis).Theeffluentfromabio-digesterwasappliedevery7days,atratesequivalentto150kgN/ha.Survivalratewashigherinpondsfertilizedwitheffluentandinpondswithlowerfishdensity.Therewerenodifferencesforgaininweightandlengthduetotreatment,andnointeractionbetweenfertilizerandstockingdensity.nbsp;However,thesedatawerederivedfromrandomsamplesoffishtakenat20dayintervalsandtheresultswerepartiallyconfoundedbydifferencesamongtreatmentsinsurvival.Netfishyieldwashigherforthehigherstockingdensitybuttherewasnoeffectoffertilizationwitheffluent.Feedconversion(DMofferedetfishyield)didnotdifferamongtreatmentsbutthismeasurementwasalsoconfoundedbydifferencesinsurvivalasamountsoffeedofferedwerebasedoninitialnumbersoffishandtheaverageweightestimatedfromthesamplingat20dayintervals.Finalfishweightandnetfishyieldwerenegativelycorrelatedwithsurvivalrate.Inexperiment2,12plotsinapaddyfieldeachwithanareaof209m2wereusedtocompare4treatmentsina2x2factorialinacompletelyrandomizeddesignwith3replicates.Thefirstfactorwaswithorwithoutfeedsupplement;thesecondfactorwasdifferentstockingdensitiesof3or5fishperm2.Ineachplotofpaddytherewasatrench11mwidex1minlengthx1mdeepalongonesideofeachplot.Thefeedsupplementwasthesameasinexperiment1.Allpaddyplotswerefertilizedwitheffluentfromabio-digesterevery7daysattherateof150kgNperha.Survivalratewasnotaffectedbysupplementationbuttherewasatendency(P=0.10)forittobeloweronthehigherstockingrate.Bothfinalweightoffishandthenetfishyieldwereincreasedbysupplementationandbystockingratewithnointeractionbetweenthetreatments.TheFCR(forthosepaddiesthatreceivedfeedsupplementation)wasnotaffectedbystockingrate.Inconclusionitwouldseemthatinrice-fishsystems,supplementationisnotanappropriateintervention,inviewofthelowerefficiencyofuseofthesupplement.Thus,fortheadditional43kgofnetfishyield(123-80)inexperiment2,nbsp;theamountoffeedprovidedwasonaveragenbsp;358kg(7.5/209*10000),thatisabout7.5kgfeedper1kgofnetfishyield.nbsp;nbsp;Measuresthatleadtoenhancementofthenaturalfeedsupply(eg:fertilizationwithbio-digestereffluent)wouldseemtobemoreappropriatetechnology.