歪尾，又称歪形尾，鱼类的一种尾鳍，常见于鲨类和鲟类，歪尾外形和内部结构均不对称。

外观：歪尾上叶较大，向背侧延伸，下叶较小，不延伸.内部结构：歪尾的鳍片内均有骨骼支持，但不对称.上叶内有尾椎骨、尾上骨及尾下骨支持，下叶仅有尾下骨支持.歪尾的尾柄细长，能强有力地摆动尾鳍，故鲨类和鲟类是善于快速游泳的鱼类.GOOGLE英文翻译:Also known as the crooked-shaped tail. A kind of tail fins of fish commonly found in sharks and sturgeons. Crooked tail shape and internal structure are asymmetrical. Appearance: crooked tail lobe large, extending to the dorsal, lower lobe small, does not extend . Internal structure: crooked tail fins were bones inside the support, but asymmetric. on the leaves of a tail vertebrae, the tail bone and tail bone under the support of only the end of the next lower lobe of bone support. crooked tail slender caudal peduncle can be a powerful swing tail fins, so shark class and the class is good at fast-swimming sturgeon fish.