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高中英语现代文背诵篇章34RaisingOysters素材.doc

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34RaisingOystersIntheoysterswereraisedinmuchthesamewayasdirtfarmersraisedtomatoes-bytransplantingthem.Firstfarmersselectedtheoysterbedclearedthebottomofoldshellsandotherdebristhenscatteredcleanshellsabout.Nextthey”planted”fertilizedoystereggswhichwithintwoorthreeweekshatchedintolarvae.Thelarvaedrifteduntiltheyattachedthemselvestothecleanshellsonthebottom.Theretheyremainedandintimegrewintobabyoysterscalledseedorspat.Thespatgrewlargerbydrawinginseawaterfromwhichtheyderivedmicroscopicparticlesoffood.Beforelongfarmersgatheredthebabyoysterstransplantedthemoncemoreintoanotherbodyofwatertofattenthemup.Untilrecentlythesupplyofwildoystersandthosecrudelyfarmedweremorethanenoughtosatisfypeople’sneeds.Buttodaythedelectableseafoodisnolongeravailableinabundance.Theproblemhasbecomesoseriousthatsomeoysterbedshavevanishedentirely.Fortunatelyasfarbackastheearly1900’smarinebiologistsrealizedthatifnewmeasureswerenottakenoysterswouldbecomeextinctoratbestaluxuryfood.Sotheysetupwell-equippedhatcheriesandwenttowork.Buttheydidnothavetheproperequipmentortheskilltohandletheeggs.Theydidnotknowwhenwhatandhowtofeedthelarvae.Andtheyknewlittleaboutthepredatorsthatattackandeatbabyoystersbythemillions.Theyfailedbuttheydoggedlykeptatit.Finallyinthe1940’sasignificantbreakthroughwasmade.Themarinebiologistsdiscoveredthatbyraisingthetemperatureofthewatertheycouldinduceoysterstospawnnotonlyinthesummerbutalsointhefallwinterandspring.Latertheydevelopedatechniqueforfeedingthelarvaeandrearingthemtospat.Goingstillfurthertheysucceededinbreedingnewstrainsthatwereresistanttodiseasesgrewfasterandlargerandflourishedinwaterofdifferentsalinitiesandtemperatures.Inadditionthecultivatedoys