Fin, a first-degree Chinese character, is pronounced fin (qí)

Explanation of fin:

Fins are external organs on the body of a fish, supported by appendicular skeletons, usually distributed on the carapace and tail, and are the main instruments of locomotion and balance of 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.

From the point of view of the evolution of fins, it is generally believed that the odd fins came first, followed by the even fins. According to the fossil and embryonic development of fish, the odd fins originate from a continuous fold of skin that runs from the head through the back, then around the tail to the anus, where it splits into various types of fins as a result of long-term movement.

The fins later evolved fin rays, which supported and strengthened the functions of the fins. The even fins originated as two long lateral folds on either side of the abdomen, which degenerated as the fish evolved, leaving only the head and tail, the one behind the head being the pectoral fin and the one in front of the tail being the ventral fin.

The fins generally consist of an endoskeleton and fin rays, with muscles and membranes attached. The fins are long, thin strips supported within the fins, and each fin consists of two strips, right and left, which can be separated by boiling. The fins of fish can be divided into two main groups, angular fins, which are neither branched nor segmented, as in cartilaginous fishes;

the other group is bony fins (also known as squamous fins), which are fins derived from scales, and are found in hard-boned fishes. Some are neither branched nor segmented and hard, and cannot be separated after boiling, called spines; some are segmented but not branched and hard, and can be separated from side to side after boiling, called pseudospines; some are both segmented and branched and soft; and some are segmented but not branched and soft.

The fins are the organs of locomotion in fish and play the role of "helmsman". They are made up of membranes and spines, and can be divided into pectoral, ventral, dorsal and anal fins, and caudal fins according to their length. Relying on the fins, the body can be maintained in the water flat swimming speed, some fish in the jump out of the water can even be fins as a gliding tool, such as the flying fish