Fish Fins

All species of fish have fins in one form or another. The fins are critically important appendages that enable the fish to propel, stabilize, maneuver, and stop itself. In some cases, fins have developed to protect the fish as well. Again, depending on the type of fish and the habitat it lives in, the fins can take on many shapes and functions. Bottom, sedentary, or slower moving fish typically have rounded fins, while faster, open water fish generally have longer, pointed fins.

Fish fins are either paired or unpaired. The only fins that come in pairs are the pectoral and pelvic fins, while the dorsal, anal, and caudal fins are unpaired. The pectoral fins are the paired fins closest to the head. The fish uses these fins to stabilize, turn, maneuver, hover, and swim backwards. These fins are generally found just behind or below the gills on each side of the fish, under the midline of the body.

The pelvic fins are also paired and vary the most in position. In some fish, they lie under the fish toward the rear. In others, such as many tropical species, the pelvics are closer to the head under the pectorals. In general, the pelvic fins act as brakes while aiding in stabilizing and turning the fish.

The dorsal and anal fins are unpaired fins that are found protruding from the top and bottom of the fish, respectively. Dorsal fins may be elongated or short, elaborate or simple, singular or multiple. In some species of fish, the dorsal or anal fin may be completely lacking. Both fins help stabilize the fish and keep it moving straight.

The caudal or tail fin is a single fin largely responsible for propelling the fish forward. This fin can also assist in turning and braking. Faster fish have deeply forked caudal fins, while many deep-bodied and bottom fish have square or rounded tail fins.

In general, the main supporting structures of fish fins are soft rays. However, anyone who has handled a fish knows that the dorsal, anal, pectoral, or pelvic fins of many species also have spines. These sharp, bony structures provide protection against predators and can certainly hurt us as well.