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According to McGinn, aquaculture will most probably become ______ in the future.
A．the major resource of seafood
B．a pollution-flee industry
C．the major source of protein
D．an industry of sustainable development
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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.
All the following statements are the reasons why commercial aquaculture is pushed forward EXCEPT
A．the human population is increasing fast.
B．the wild fish stocks are decreasing due to over fishing.
C．the cost of developing aquaculture is comparatively low.
D．there is no improvement in conventional farm production.
The increasing number of citizen groups, businesses and governments taking an active interest in slowing down the destruction and pollution of the ocean is encouraging, says senior researcher and author Anne Plait McGinn, citing a host of efforts already under way.
(1) Unilever, which controls 20 percent of the whitefish market in Europe and US, has agreed to buy only fish caught and produced in an environmentally sustainable manner.
(2) Volunteers in the Philippines, Thailand, India and Ecuador are replanting mangrove areas to repair earlier damage from shrimp faming.
(3) In northern Sulawesi, citizens have cleared coral reefs of harmful invasive species.
(4) The United States and Canada have each banned oil drilling on large portions of their continental shelves.
On the downside, Safeguarding the Health of Oceans says that seven out of ten commercial fish species are fully or overexploited and even worse, many of their spawning grounds have been cleared to make room for shrimp ponds, golf courses and beach resorts. Habitat degradation, resulting from development, agricultural runoff, sewage pollution and destructive fishing practices has led to a tripling in the number of poisonous algae species identified by scientists, increasing fish kills, beach closures, and economic losses.
The impact on the economy is significant. People obtain an average of 16 percent of their animal protein from fish, and people in developing countries are extremely dependent on reef fisheries for both food and income. Tourism accounts for a large piece of coastline economies and medicines are being found in reef ecosystems every day. Even toothpaste and ice cream depend on the gel-forming properties of brown algae.
The problems facing the oceans are legion: the marine conversation community is fragmented, bans on destructive activities are routinely ignored, too many regulatory organizations have a development-first mindset and enforcement and oversight are ineffective, if not altogether lacking.
Oceans need to be protected locally, nationally and internationally, according to McGinn. Right now, the United Nations General Assembly spends just one day a year covering issues that affect more than half of the planet. The report suggests that a tax of one tenth of one percent on industrial and recreational ocean activities would generate $ 500 million a year, more than five times the annual budgets the International Maritime Organization and the Fisheries Department of the U.N. Food and Agriculture Organization.
However, the most productive areas of the ocean are under national jurisdiction and 80 percent of oceanic pollution originates on land. This means that addressing global marine issues requires strong national and local policies.
Problems remain far from resolved.
The word "sustainable" in paragraph 2 is closest in meaning to______.
A．maintainable
B．reasonable
C．understandable
D．respectable
【填空题】![【填空题】[图]Fill in the blanks according to the pa...【](http://static.jiandati.com/1ae9caa-chaoxing2016-799371.png)
Fill in the blanks according to the passages.![【填空题】[图]Fill in the blanks according to the pa...【](http://static.jiandati.com/f7f77a8-chaoxing2016-799445.png)
A、According to how much time he has worked.
B、According to the level of output.
C、According to how many items are sold.
D、According to how many clients are contacted.
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