Apr 21, 2009
Newcastle, Australia

Fins, what are they? What they are for? What fin is which?

Most people when they hear the term fin used when referring to a fish, automatically know that that refers to the boney but also fleshy appendages. But what are they called and what are they used for? Well, that is what we are here to discuss.

Each fin has it's own purpose and it's own name.

Lets start with across the top of the body.

The Dorsal Fin.
This is the fin on the top of the fish.
The purpose of this fin is to help the fish maintain it's balance.

The Adipose Fin.
This fin is located behind the Dorsal but before the Caudal or Tail Fin.
Not all fish possess this fin and it is not certain the exact purpose of this fin. It is found more predominantly in fish from high flowing rivers leading some to believe that the Adipose Fin can act like a second dorsal fin. There has been some experimental evidence where the Adipose Fin has been removed from juvenile fish that the removal of this fin has subsequently reduced their swimming abilities in varied flow rates. While others tend to believe that it is a just a piece of useless fatty tissue. I guess this will remain uncertain until some more conclusive studies have been done on the issue.

Now to the lower fins.

The Pectoral Fins.
These fins are paired (meaning one either side) and are placed behind the gills. These fins can become quite hairy (or spikey) and become quite a useful clue in sexing some species of Loricariidae.
They are used to control direction and manouverability.

The Pelvic Fins .
These fins are also paired and placed toward the rear of the body in Plecos, just before the anal fin. In other species of fish these can also be placed almost directly below the Pectoral Fins.
The purpose of these fins is to control the up/down motion of the fish. They are also used by Plecos to "fan" their eggs and Corydora's species can also be used to hold the eggs during spawning.

The Anal Fin.
This fin is located behind the Pelvic Fins and before the Caudal fin. In Plecos these are noticeably smaller than those on most other fish especially Cichlids.
It is also used to help stablise the fish. Although some fish species which have the larger Anal Fin it can be used for propulsion.

The Caudal Fin.
This fin is also called the Tail Fin. It's location is pretty self explanatory being located at the very rear of the fish.
This fin is used for the purpose of propulsion. There are variations in tail shape depending on the species of fish.
There are the long continuous fins that are more commonly found on eels etc. These give the fish the ability to navigate through tight spots with ease.
Then there is the Forked Tail, this is most commonly found on fish that continuously swim.
Fish with rounded tails (like Frontosa) are usually slower but are stronger swimmers.
While fish with a crescent moon shape tail are the type of fish that can swim at speed for a long length of time.
And fish with a more squared tail are also strong swimmers but are generally slower.

Fin Extensions
There are a few species of fish which exhibit this natural trait, for example the Royal Whiptail with it's extended Caudal fin and deepsea fish such as the Tripod fish which uses it's extended Pectoral fins to catch its prey. The actual use of the extended caudal fins is not fully understood. As it is a natural occurance there is some speculation that it is used to attract members of the opposite sex and or to act as feelers while the fish attempts to move backwards. Although there is no evidence to support this.
Tail Extensions also appear on other aquarium fish such as the swordtail or emporer tetra and is used as a way of sexing the fish.
In the majority of Ornamental Fish this has been genetically enhanced for apppearance (eg. Long Fin Bristlenose) which also results in the fish unable to swim aswell as the standard variation of the species.



Pleco Profiles Team - RIP FRIEND
May 1, 2009
Spot on

I stand in awe again a article of outstanding use.

If only I could get my bum off the seat and write some thing as I am always promising to do

Adipose fin is suspected to be a fat fin in some fish ie a reserve of fat for times were food is scares.

Adipose is Greek for fat I believe?

Regards Bob