I. Dorsal fin

The dorsal fin of a goldfish is a balancing organ that maintains the body in an upright position to keep it from tilting from side to side. Without the dorsal fin, it's like a boat without a rudder; it can't swim in a straight line.

Two, pectoral fins

Located near the gill cover, a pair of pectoral fins, mainly deceleration, change direction and paddling, can be used as a breeding season to distinguish between male and female signs, the male fish fins will have a star, while the female fish will not have.

Goldfish decelerate and reverse by paddling the pectoral fins, at this time the caudal fin is not able to send force. When the caudal fin is not in motion, the pectoral fins open to the sides of the fish and make a back-and-forth swing, the fish moves forward, and when one side of the pectoral fin swings the fish turns to the side that is not moving. If lost, the fish body will sway from side to side, equivalent to the forelimbs of higher vertebrates.

Three, ventral fins

Between the pectoral and anal fins there is a pair of ventral fins, mainly as a rudder to stabilize the direction of the rudder, which is even though the aviation of many aircraft have ventral wings.

Four, anal fins

Acute fins are also used to stabilize the direction, and also useful for breeding, when the male fish's anal fins are shivering, the female fish's eggs will come out. Some species have a single anal fin, some have a double anal fin, and some have no anal fin, and the double anal fin is generally considered to be an excellent trait.

Fifth, the caudal fin

The caudal fin is the propeller of the goldfish, no matter whether it is a grass goldfish or a tiger, Ryukin, want to swim by the caudal fin. But note that the caudal fin is used to move forward, if you want to retreat, the caudal fin is not used. Later, after the goldfish had a double caudal fin, the stability was greatly increased.

Expanded Information

In general, the emergence of fins can be divided into three phases:

Phase I: Primitive fins or fin folds developed along the dorsal and abdominal midline in primitive chordates such as amphioxus, and at this time, there were no articulated bone structures.

Stage 2: The primitive fins without spiracles begin to degenerate, with the appearance of complete odd fins and primitive even fins, as in the hagfish.

Stage 3: Endoskeletal spoke bones and exoskeletal formation of fins are evident, e.g., sevengill and blind eels. The endoskeleton and exoskeleton are slightly differentiated prior to the formation of the fins, and as the fins gradually form, the endoskeleton and exoskeleton develop in the same pattern and form separate dorsal, anal, and caudal fins.