首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
More and more of the world’s supply of seafood is coming from farms. Although 80% of the world’s seafood comes from marine ha
More and more of the world’s supply of seafood is coming from farms. Although 80% of the world’s seafood comes from marine ha
admin
2010-05-25
102
问题
More and more of the world’s supply of seafood is coming from farms.
Although 80% of the world’s seafood comes from marine harvests, there is a major shift under way toward aquaculture now.
Nearly 40% of salmon marketed today are raised in captivity, compared with 6% a decade ago. Forty percent of all clams, oysters, and mussels are produced in farm environments, along with 65% of freshwater fish. Between 1990 and 1996, fish-farming production rose from 12.4 million to 23 million tons worldwide, writes Anne Platt McGinn in an article for World Watch magazine.
"The fact that world seafood supplies continue to increase at all is due almost entirely to the phenomenal growth in aquaculture," says McGinn, a research associate at the World Watch Institute. Commercial aquaculture is driven by rising human population at a time when over harvested wild fish stocks are in decline and conventional farm production has leveled off.
Biotechnology is contributing to high-yield aquaculture through transgenics—the transfer of genes from one species to another. Researchers introduce desirable genetic traits into fish, creating hardier stocks. For example, some species of fish have a protein that allows them to live in Arctic waters. By transplanting this "anti-freeze" gene into other species, researchers have created more fish that can survive in extremely cold water, according to Ag-West Biotech, Inc., in Saskatchewan, Canada.
Biotechnologists are attempting to improve a wide range of genetic traits in fish used for aquaculture, developing fish that are larger and faster-growing, more efficient in converting feed into muscle, more tolerant of low oxygen levels in water, and better able to resist disease.
Researchers also are seeking plant-based sources of food as a more efficient alternative to fishmeal. The use of plant protein on fish farms could take some of the pressure off wild fish stocks and address the problem of phosphorous pollution because plants do not contain high phosphorus levels. Wheat, canola, and canola oil are being used as alternative feed for aquaculture, according to Ag-West Biotech, Inc.
While aquaculture produces a reliable source of protein, the industry is rife with environmental problems, asserts McGinn. Perhaps the biggest concern is water pollution: Fish waste and uneaten food accumulates at farm sites and can float directly downstream into water supplies. Farm-related nutrient wastes as well as nitrogen and phosphorus also promote the spread of algal "blooms" that deplete oxygen and kill marine life.
Aquaculture is also an inefficient user of resources, McGinn charges. Fish farms need protein feed, andabout 17% of ocean fish, an over harvested wild resource, becomes food for captive-bred fish. "An estimated five kilograms of oceanic fish reduced into fishmeal are required to raise one kilogram of farmed ocean fish or shrimp, representing a large net protein loss," says McGinn.
Fish fanning does not have to be an inefficient or polluting industry. McCdnn predicts that many consumers will choose sustainably produced fish in the future, just as they prefer dolphin-free tuna today.
Biotechnology has already enabled more fish to
选项
A、change feed into muscle more efficiently.
B、stand low oxygen levels in water.
C、tolerate extremely cold water.
D、grow larger and faster.
答案
C
解析
细节题。第5段末句表明利用转基因技术成功培育出抗冻能力强的鱼类,故选C。
转载请注明原文地址:https://kaotiyun.com/show/Er2K777K
0
专业英语四级
相关试题推荐
Onesummernight,onmywayhomefromworkIdecidedtoseeamovie.Iknewthetheatrewouldbeair-conditionedandIcouldn’t
Onesummernight,onmywayhomefromworkIdecidedtoseeamovie.Iknewthetheatrewouldbeair-conditionedandIcouldn’t
Migrationisusuallydefinedas"permanentorsemipermanentchangeofresidence".Thisbroaddefinition,ofcourse,wouldinclud
Doesusingawordprocessoraffectawriter’sstyle?Themediumusuallydoesdosomethingtothemessageafterall,evenifMars
InAmerica,olderpeoplerarelylivewiththeiradultchildren.Butinmanyothercultureschildrenareexpectedtocare【C1】____
WhydidmarinesgatheronMonday?
Itisunfortunatethatnowviolenceandcartoons______themostdistinctivecharacteristicofchildren’sprograms.
______humanbehaviormaybecausedbyeatingsubstancesthatupsetthedelicatechemicalbalanceinthebrain.
Individualism,independence,andself-relianceareperhapsthemostdistinctiveAmericancharacteristic.American"individualism
PerhapsthemostheatedargumentacrosstheUnitedStatestodayisthedeathpenalty.Manyarguethatitisan【C1】______deterr
随机试题
不属于汉语特点的是()
心脏按压的方法不正确的是
女性,35岁,劳累时心悸、气短,休息后可缓解,反复双下肢轻度水肿一年。半月前因受凉后咳嗽,咳白色泡沫痰及少许黏痰,同时伴心悸、气短、不能平卧来急诊。体检:呼吸22次/分,口唇发绀,心率120次/分,心律绝对不规则,心尖区闻及SM3/6级杂音和DM,双肺对称
对于股骨头骨软骨病病理变化叙述正确的是
利用施工图改绘竣工图,必须标明变更依据;凡施工图结构、工艺、平面布置等有重大改变,或变更部分超过图面( )的,应当重新绘制竣工图。
在个人住房贷款中,若保证人向第三方提供超出其自身负担能力的担保的,银行应限期要求借款人更换贷款银行认可的新的担保。()
教育是培养人的社会实践活动,这一本质决定了教育既是一个相对独立的系统,又是一个复杂开放的系统。()
放弃可能明显导致亏损的投资项目属于风险对策中的()。
Panel和Applet的默认布局管理器是
Peoplewhodon’tunderstandwhattheiremployersexpectthemtodomaybeheadedforoneofthemostcommonandyetmostavoidab
最新回复
(
0
)