In the oysters were raised in much the same way as dirt farmers raised tomatoes- by transplanting them. First, farmers selected the oyster bed, cleared the bottom of old shells and other debris, then scattered clean shells about. Next, they planted fertilized oyster eggs, which within two or three weeks hatched into larvae. The larvae drifted until they attached themselves to the clean shells on the bottom. There they remained and in time grew into baby oysters called seed or spat. The spat grew larger by drawing in seawater from which they derived microscopic particles of food. Before long, farmers gathered the baby oysters, transplanted them once more into another body of water to fatten them up.
Until recently the supply of wild oysters and those crudely farmed were more than enough to satisfy peoples needs. But today the delectable seafood is no longer available in abundance. The problem has become so serious that some oyster beds have vanished entirely.
Fortunately, as far back as the early 1900s marine biologists realized that if new measures were not taken, oysters would become extinct or at best a luxury food. So they set up well-equipped hatcheries and went to work. But they did not have the proper equipment or the skill to handle the eggs. They did not know when, what, and how to feed the larvae. And they knew little about the predators that attack and eat baby oysters by the millions. They failed, but they doggedly kept at it. Finally, in the 1940s a significant breakthrough was made.
The marine biologists discovered that by raising the temperature of the water, they could induce oysters to spawn not only in the summer but also in the fall, winter, and spring. Later they developed a technique for feeding the larvae and rearing them to spat. Going still further, they succeeded in breeding new strains that were resistant to diseases, grew faster and larger, and flourished in water of different salinities and temperatures. In addition, the cultivated oysters tasted better!
2014人教新目标英语八下 unit 8《Have you read treasure island yet》学案
2014人教新目标英语八下 unit2《I’ll help to clean up the city》parksperiod 1导学案
2014人教新目标英语八下 unit 7《What’s the highest mountain in the world》同步辅导及练习
2014人教新目标英语八下 unit 8《Have you read treasure island yet》同步单元测试
2014人教新目标英语八下 unit 7《What’s the highest mountain in the world》period 2教案
2014人教新目标英语八下 unit 7《What’s the highest mountain in the world》period 2导学案
2014人教新目标英语八下 unit 7《What’s the highest mountain in the world》period 1导学案
2014人教新目标英语八下 unit4《Why don’t you talk to your parents》(第1课时)教案
2014人教新目标英语八下 unit 7《What’s the highest mountain in the world》知识点汇总
2014人教新目标英语八下 unit3《Could you please clean your room》(第5课时)导学案
2014人教新目标英语八下 unit2《I’ll help to clean up the city》parks教案2
2014人教新目标英语八下 unit 7《What’s the highest mountain in the world》period 5教案
2014人教新目标英语八下 unit2《I’ll help to clean up the city》parksperiod 3导学案
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2014人教新目标英语八下 unit 7《What’s the highest mountain in the world》lesson plan 5教案
2014人教新目标英语八下 unit3《Could you please clean your room》(第4课时)导学案
2014人教新目标英语八下 unit 7《What’s the highest mountain in the world》同步检测题
2014人教新目标英语八下 unit1《What’s the matter》(第2课时)导学案
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2014人教新目标英语八下 unit 7《What’s the highest mountain in the world》period 3教案
2014人教新目标英语八下 unit 8《Have you read treasure island yet》单元综合检测题2
2014人教新目标英语八下 unit 7《What’s the highest mountain in the world》period 1教案
2014人教新目标英语八下 unit3《Could you please clean your room》(第3课时)导学案
2014人教新目标英语八下 unit 7《What’s the highest mountain in the world》必背词组及句子
2014人教新目标英语八下 unit 7《What’s the highest mountain in the world》单元词汇
2014人教新目标英语八下 unit1《What’s the matter》(第5课时)导学案
2014人教新目标英语八下 unit 7《What’s the highest mountain in the world》period 4教案
2014人教新目标英语八下 unit 7《What’s the highest mountain in the world》period 3导学案
2014人教新目标英语八下 unit3《Could you please clean your room》(第6课时)导学案
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