Fin pinyin: qí.

Fin (qí) refers to the fin-like or paddle-like appendages of fish and some other aquatic animals, which serve for propulsion, balance, and guidance. Fins have evolved in many different organisms, especially in most fish. Among mammals, whales and sea lions have fins. There are also a few reptiles, such as sea turtles, and birds, such as penguins. Sometimes species without fins grow limbs shaped like fins because of developmental abnormalities.

Fins are external organs on the body of a fish, supported by appendicular skeletons, usually found on the carapace and tail, and are the primary means of locomotion and balancing the body. The fins can be generally divided into two categories, one is the unpaired odd fins, located on the back, tail and behind the anus, including the dorsal, caudal and anal fins; the other is the left and right pairs of even fins, located on both sides of the body, including the pectoral fins and ventral fins.

Introduction to Shape

Fins, the locomotor organs of fish and other aquatic vertebrates adapted to life in the water. Fins generally consist of skin, soft fin rays, and hard, non-segmented fin spines. Due to the different attachment sites, there are dorsal, anal, caudal, pectoral and ventral fins.

The first three of these are not paired and are called "odd fins", while the last two are generally paired with the front and hind limbs of other vertebrates and are called "even fins". With the living environment, living habits of different, in the long-term evolutionary process of some of the fin function and shape of the fish changed, and even some fin degradation or disappearance.