又称正形尾.鱼类的一种尾鳍，常见于硬骨鱼类.正尾的外形完全对称，形成相似的两叶鳍片.鳍片由软鳍条支持，无硬棘.正尾的内部结构不对称：尾椎骨末端上翘；尾下骨较尾上骨发达.正尾的形态与游速有密切关系，如鳍片深凹，正尾呈新月形，尾柄细而有力则游速快、游程长，如金枪鱼、鲐鱼、鲭鱼等.如鳍片中间凹陷，尾柄无明显变化，则游速不快，如鲤鱼等.GOOGLE英文翻译:Also known as being shaped tail. A kind of tail fins of fish commonly found in bony fish. Are completely symmetrical shape of the end to form a similar two leaves Fins. Fin supported by the soft dorsal fin, no hard spine. Are at the end of the internal Structural Asymmetry: tailbone end of the upturned; tail bone under the well-developed compared with the tail bone. are at the end of morphology and swim speed are closely related, such as Deep fins are crescent-shaped tail, caudal peduncle is small and powerful travel speed quick, run-length, such as tuna, mackerel, mackerel and so on. such as the fin the middle of depression, caudal peduncle no significant change, then the travel speed unpleasant, such as carp and so on.