Fins And What They Are Called.

Rachel posted something the other day about a fish with a poorly fin. She called it the side fin, which isn't desperately helpful, so I thought I would post this to explain what the various fins are called.

The obvious one first, the tail fin. Tail fin is OK, but technically it is the caudal fin. The rayed fin or fins on the top of the fish are dorsal fins. Most fish have one of these, but some have multiple ones, Cod for example. Some fish have a small rayless fin on the top between the dorsal and caudal fins, tetras for example. This is the adipose fin.

Now, along the bottom from the caudal fin towards the gills. First we have the anal fin, because it's close to the fishes bum! Next, a pair of fins called the ventral fins. Near where a fishes hips would be if it had any hips! Finally the ones just behind the gills are called the pectoral fins.

The actual arrangement of these fins can vary from species to species, but this info should be enough to identify them.

Some fish do have modified fins, as Steve said, and you wouldn't think some of them are actually fins. For example, the long thread like things dangling under a gourami are the ventral fins, while the anal fin is very long and runs almost the whole length of the body.