新概念优美背诵短文：饲养牡蛎.docx

新概念优美背诵短文：饲养牡蛎关于新概念优美背诵短文50篇：饲养牡蛎RaisingOysters饲养牡蛎Inthepastoysterswereraisedinmuchthesamewayasdirtfarmersraisedtomatoes-bytransplantingthem.First,farmersselectedtheoysterbed,clearedthebottomofoldshellsandotherdebris,thenscatteredcleanshellsabout.Next,they”planted”fertilizedoystereggs,whichwithintwoorthreeweekshatchedintolarvae.Thelarvaedrifteduntiltheyattachedthemselvestothecleanshellsonthebottom.Theretheyremainedandintimegrewintobabyoysterscalledseedorspat.Thespatgrewlargerbydrawinginseawaterfromwhichtheyderivedmicroscopicparticlesoffood.Beforelong,farmersgatheredthebabyoysters,transplantedthemintootherwaterstospeeduptheirgrowth,thentransplantedthemoncemoreintoanotherbodyofwatertofattenthemup.过去人们饲养牡蛎的方式很大程度上类似于田地里的农夫种植蕃茄——通过移植来饲养它们。首先，农夫选好牡蛎苗床，清除底部的旧壳和其它杂物，然后四处撒播干净的壳。接着，他们“栽种”已受精的牡蛎卵。这些卵在2-3周内会孵化成幼贝。幼贝一直漂流直到粘在苗床底部干净的壳上为止。它们会呆在那儿并逐渐长成小牡蛎。我们称之为种子或贝苗。贝苗吸进海水中的微小生物作为食物从而越长越大。不久之后，农夫将这些小牡蛎收集起来，把它们移种进其他的水域加快其生长，然后再次将它们移种进另外的水域以使其肥壮起来。Untilrecentlythesupplyofwildoystersandthosecrudelyfarmedweremorethanenoughtosatisfypeople’sneeds.Buttodaythedelectableseafoodisnolongeravailableinabundance.Theproblemhasbecomesoseriousthatsomeoysterbedshavevanishedentirely.直到最近，野生的以及人工饲养的牡蛎完全能够满足人们的需要。但是今天这种可口的海味已不再大量存在。这个问题已经变得如此严重以至于一些牡蛎苗床已完全消失。Fortunately,asfarbackastheearly1900’smarinebiologistsrealizedthatifnewmeasureswerenottaken,oysterswouldbecomeextinctoratbestaluxuryfood.Sotheysetupwell-equippedhatcheriesandwenttowork.Buttheydidnothavetheproperequipmentortheskilltohandletheeggs.Theydidnotknowwhen,what,andhowtofeedthelarvae.Andtheyknewlittleaboutthepredatorsthatattackandeatbabyoystersbythemillions.Theyfailed,buttheydoggedlykeptatit.Finally,inthe1940’sasignificantbreakthroughwasmade.幸运的是，早在20世纪初期海洋生物学家们就意识到如果不采取新的措施，牡蛎将会灭绝或至少会变为一种奢侈的食品。因此他们建造了装备良好的孵卵场所并开始工作。但是他们尚没有适当的.装置或技术来处理牡蛎卵。他们不知道何时、用什么以及如何喂养幼贝。他们对捕食数百万幼小牡蛎的动物天敌也所知无几。他们失败了，但他们顽强地坚持了下来。终于，在20世纪40年代，一个重要的突破性的进展产生了。Themarinebiologistsdiscoveredthatbyraisingthetemperatureofthewater,theycouldinduceoysterstospawnnotonlyinthesummerbuta