鱼的介绍英语.doc

A fish is a water-dwelling vertebrate with gills that doesnt change form, as amphibians do, during its life. Most are cold-blooded, though some (such as some species of tuna and shark) are warm-blooded. There are over 29,000 species of fish, making them the most diverse group of vertebrates. 鱼用鳃是一种水生脊椎动物，不改变形式，两栖动物，在其生命周期。大部分都是冷血，虽然有些（如某些种类的金枪鱼和鲨鱼）是温血动物。有超过29,000种鱼类，使他们最多样化的脊椎动物。Taxonomically, fish are a paraphyletic group whose exact relationships are much debated; a common division is into the jawless fish (class Agnatha, 75 species including lampreys and hagfish), the cartilaginous fish (class Chondrichthyes, 800 species including sharks and rays), with the remainder classed as bony fish (class Osteichthyes).分类学上，鱼是一种系群，其备受争议的确切关系;一个共同的分工是无颌鱼（类无颌类，75种，包括七鳃鳗和盲鳗），软骨鱼类（软骨鱼，800种，包括鲨鱼和鳐鱼），其余归类为硬骨鱼（类硬骨鱼纲）。Fish come in different sizes, from the 16 m (51 ft) whale shark to a 8 mm (just over of an inch) long stout infantfish. Many types of aquatic animals named fish are not true fish, and in the case of animals such as jellyfish and cuttlefish, are not even vertebrates. Other marine creatures that have in the past been considered fish, like dolphins, are actually mammals.鱼有不同的大小，从16米（51英尺）到8毫米（刚刚超过四分之一英寸）长的粗壮的infantfish的鲸鲨。水生动物的许多类型的名为“鱼”不是真正的鱼，在动物，如水母和乌贼的情况下，甚至不脊椎动物。其他海洋生物，在过去被认为是鱼，像海豚一样，实际上是哺乳动物。Although most fish are exclusively aquatic and cold-blooded, there are exceptions to both cases. Fish from a number of different groups have evolved the capacity to live out of the water for extended periods of time. Of these amphibious fish some such as the mudskipper can live and move about on land for up to several days. Also, certain species of fish maintain elevated body temperatures to varying degrees. Endothermic teleosts (bony fishes) are all in the suborder Scombroidei and include the billfishes, tunas, and one species of primitive mackerel (Gasterochisma melampus). 虽然大多数鱼只水生和冷血这两种情况下，也有例外。从许多不同的组的鱼已经进化长时间住出来的水的容量。这些两栖鱼如弹涂鱼生活和移动关于土地长达数天。此外，某些种类的鱼保持不同程度的体温升高。吸热硬骨鱼类（硬骨鱼类）所有亚Scombroidei中，并包括旗鱼，金枪鱼，一个物种的“原始”鲭鱼（Gasterochisma MELAMPUS）All sharks in the family Lamnidae shortfin mako, long fin mako, white, porbeagle, and salmon shark are known to have the capacity for endothermy, and evidence suggests the trait exists in family Alopiidae (thresher sharks). The degree of endothermy varies from the billfish, which warm only their eyes and brain, to bluefin tuna and porbeagle sharks who maintain body temperatures elevated in excess of 20 C above ambient water temperatures. See also gigantothermy. Endothermy, though metabolically costly, is thought to provide advantages such as increased contractile force of muscles, higher rates of central nervous system processing, and higher rates of digestion.在家庭中的鼠鲨科鲨鱼 - 鲭shortfin，长鳍鲭，白，鼠鲨和鲑鲨 - 被称为有能力为温性，有证据表明性状存在在家庭Alopiidae（长尾鲨）。温性的程度不同，温暖他们的眼睛和大脑，以维持体温超过20C以上的环境水温升高的蓝鳍金枪鱼和鼠鲨鲨旗鱼。另见gigantothermy。温性，虽然代谢昂贵，被认为是提供了有利条件，如增加肌肉的收缩力，中枢神经系统处理率较高，消化率较高。Fish are an important source of food in many cultures. Other water-dwelling animals such as mollusks, crustacean