高中英语现代文背诵篇章34RaisingOysters素材.doc

34RaisingOystersIntheoysterswereraisedinmuchthesamewayasdirtfarmersraisedtomatoes-bytransplantingthem.First,farmersselectedtheoysterbed,clearedthebottomofoldshellsandotherdebris,thenscatteredcleanshellsabout.Next,they”planted”fertilizedoystereggs,whichwithintwoorthreeweekshatchedintolarvae.Thelarvaedrifteduntiltheyattachedthemselvestothecleanshellsonthebottom.Theretheyremainedandintimegrewintobabyoysterscalledseedorspat.Thespatgrewlargerbydrawinginseawaterfromwhichtheyderivedmicroscopicparticlesoffood.Beforelong,farmersgatheredthebabyoysters,transplantedthemoncemoreintoanotherbodyofwatertofattenthemup.Untilrecentlythesupplyofwildoystersandthosecrudelyfarmedweremorethanenoughtosatisfypeople’sneeds.Buttodaythedelectableseafoodisnolongeravailableinabundance.Theproblemhasbecomesoseriousthatsomeoysterbedshavevanishedentirely.Fortunately,asfarbackastheearly1900’smarinebiologistsrealizedthatifnewmeasureswerenottaken,oysterswouldbecomeextinctoratbestaluxuryfood.Sotheysetupwell-equippedhatcheriesandwenttowork.Buttheydidnothavetheproperequipmentortheskilltohandletheeggs.Theydidnotknowwhen,what,andhowtofeedthelarvae.Andtheyknewlittleaboutthepredatorsthatattackandeatbabyoystersbythemillions.Theyfailed,buttheydoggedlykeptatit.Finally,inthe1940’sasignificantbreakthroughwasmade.Themarinebiologistsdiscoveredthatbyraisingthetemperatureofthewater,theycouldinduceoysterstospawnnotonlyinthesummerbutalsointhefall,winter,andspring.Latertheydevelopedatechniqueforfeedingthelarvaeandrearingthemtospat.Goingstillfurther,theysucceededinbreedingnewstrainsthatwereresistanttodiseases,grewfasterandlarger,andflourishedinwaterofdifferentsalinitiesandtemperatures.Inaddition,thecultivatedoysterstastedbetter!