To us, the environment in which fish dwell often seems cold, dark, and mysterious. But there are advantages to living in water, and they have played an important role in making fish what they are. One is that water isn’t subject to sudden temperature changes. Therefore it makes an excellent habitat for a cold-blooded animal. Another advantage is the water’s ability to easily support body weight. Protoplasm has approximately the same density as water, so a fish in water is almost weightless. This “weightlessness” in turn means two things: One, a fish can get along with a light weight and simple bone structure, and two, limitations to a fish’s size are practically removed. Yet there is one basic difficulty to living in water—the fact that it’s incompressible. For a fish to move through water, it must actually shove it aside. Most can do this by wiggling back and forth in snakelike motion. The fish pushes water aside by the forward motion of its head, and with the curve of its body and its flexible tail. Next, the water flows back along the fish’s narrowing sides, closing in at the tail, and helping the fish propel itself forward. The fact that water is incompressible has literally shaped the development of fish. A flat and angular shape can be moved through water only with difficulty. And for this reason, fish have a basic shape that is beautifully adapted to deal with this peculiarity.

【生词摘录】

1. subject: adj. likely to be affected by something, especially something unpleasant 易受„(不快事物)影响的;易患„的[+to]
2. cold-blooded: adj. a cold-blooded animal, such as a snake, has a body temperature that changes with the temperature of the air or ground around it (动物)冷血的(如蛇)
3. protoplasm:n.[U]technicalthecolorlesssubstancethatformsthecellsof plants and animals 【术语】原生质,原浆
4. approximately: adv. (of quantities) imprecise but fairly close to correct 近 似地,大约
5. weightless: adj. having no weight, especially when you are floating in space or water(尤指在空中或水中)失重的;没有重量的
6. limitation:n.[Cusuallyplural]alimitonhowgoodsomeoneorsomething can be, what they are able to do etc(某人或物)局限,不足之处
7. incompressible: adj. impossible to compress; resisting compression 不能 压缩的
8. shove:v.topushsomeoneorsomething,inaroughorcarelessway,using your hands or shoulders(用手或肩)推,推挤,推撞
9. wiggle:v.tomovewithsmallmovementsfromsidetosideorupanddown, or make something move like this(动作较小地)摆动;扭动

10.propel: v. to move, drive, or push something forward 推动;推进;驱动 11.literally: adv. used to emphasize that something is actually true 的确,确实 12.angular: adj. having sharp and definite corners 有尖角的
13.peculiarity: n. [C]something that is a feature of only one particular place,

person, or situation(仅为某人、某地方或某情况所独有的)特点;独特性