Fish are bony scales, gill breathing, swimming through the tail and trunk and the coordination of fins swimming and feeding by the upper and lower jaws, belonging to the chordate phylum of vertebrates, generally people divide vertebrates into fish (53%), birds (18%), reptiles (12%), mammals (9%), amphibians (8%). According to the statistics of the late Canadian scholar "Nelson" in 1994, there are 24618 species of living species fish in the world, accounting for more than half of the named vertebrates, and new species of fish are constantly being discovered, with an average of about 150 species per year, which should have increased by more than 1500 species in more than a decade, and the current global named fish species are about 32100 species.
<h3>Spindle-shaped</h3>
Fish in various forms
Also known as the basic type, it is the body shape of a general fish, suitable for swimming in the water, and the whole body is spindle-shaped and slightly flattened. Among the three body axes, the head and tail axis is the longest, the dorsal and ventral axis is the second, and the left and right axes are the shortest, so that the entire body is streamlined or slightly flattened, which is conducive to reducing the resistance when moving forward in the water, so this type of fish is good at swimming. It often inhabits the middle and upper layers of water. Long-distance migrations are possible. Examples: carp, crucian carp, shark.
<h3>Side flat type</h3>
Among the three body axes of this type of fish, the left and right axes are the shortest, and the proportion of the head and tail axes and the dorsal and ventral axes is not too much, forming a symmetrical flat shape on the left and right sides, so that the entire body shape is flat and wide, so the ability to swim is worse than the spindle type, living in the middle and lower layers of the water. Long-distance migrations are rare. Such as pomfret, butterfly fish, bream, rouge, swallow fish and so on.
<h3>Stick type</h3>
eel
Also known as eel type. The head-tail shaft of this type of fish is particularly long, and the left and right axes and the ventral axis are almost equal, both are very short, so that the whole body shape is stick-shaped. Its swimming ability is stronger than that of the lateral flat type and the flat flat type. Suitable for burrowing in underwater mud and living in underwater sand and gravel.
Such as yellow eels, eels and a variety of moray eels.
<h3>Flat type</h3>
Among the three body axes of this type of fish, the left and right axes are particularly long, and the dorsal and ventral axes are very short, so that the body size is flattened up and down, and the movement is slow, which is not as flexible as the first two types, and the multi-camp benthic life. For example, stingrays, rays, trout and catfish.
In addition, some fish take on special sizes due to their adaptation to special living environments and lifestyles, such as sea dragons, sunfish, river rays, flounders, box fish, etc. Regardless of the size of the fish, it can be divided into three parts: head, trunk and tail. Neckless is characterized by the fact that the head and torso are interconnected and fixed, which is one of the differences between fish and terrestrial vertebrates, and the dividing line between the head and torso is the posterior edge of the gill cap (teleost fish) or the last pair of gill fissures (cartilaginous fish). The trunk and tail are generally demarcated by the posterior margin or the starting point of the fin, or, to be precise, at the end of the body cavity or the first caudal vertebral.
fish
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