2. Explanation The locomotor organ of fish, consisting of a spiny, hard or cartilaginous supporting membrane. According to the part where it is located, it can be divided into pectoral fins, ventral fins, dorsal fins, anal fins and caudal fins. They serve to regulate speed, change direction, etc. Fins, the locomotor organs of fish and other aquatic vertebrates adapted for life in the water. Fins are generally composed of skin, soft fin rays and hard, non-segmented fin spines. Due to the different parts of the birth, there are dorsal, anal, caudal, pectoral and ventral fins, of which the first three are not paired, known as the "odd fins", the latter two and other vertebrates are generally paired with the fore and hind limbs, known as the "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.