34 Raising Oysters
In the past 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 in other waters to speed up their growth, then 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!
雅思阅读考试要点大盘点(2)
雅思阅读考试要点大盘点(4)
雅思阅读题型应答攻略:完成图表、示意图题型
雅思阅读题型做题技巧:matching
雅思阅读考试要点大盘点(5)
雅思阅读技巧大全:Identify writers views
雅思阅读复杂句子分析(1)
雅思阅读复杂句子分析(6)
雅思阅读复杂句子分析(4)
雅思阅读题型应答攻略:完成句子题型
全面剖析雅思阅读的各类题型
雅思阅读题型应答攻略:摘要、填空题型
雅思阅读精选:奥巴马直面美国财政悬崖
雅思阅读技巧大全:Sentence completion
雅思阅读题型做题技巧:headings
雅思阅读考试的实战技巧与策略
雅思阅读复杂句子分析(5)
剑桥雅思阅读文章背景知识补充
雅思阅读的快速做题方法
雅思阅读题型做题技巧:table completion
雅思阅读题型做题技巧:填空、排序、搭配题
雅思阅读精选:印度轮奸案受害者应"被匿名"吗?
雅思阅读解题方法指导:完成句子
雅思阅读复杂句子分析(8)
雅思阅读考试要点大盘点(1)
雅思阅读T/F/NG的快速判断法
雅思阅读题型应答攻略:段落标题
雅思阅读题型做题技巧:short answer questions
提高雅思阅读能力的方法(英)
雅思阅读题型做题技巧:summary
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |