Fish Anatomy

Cyphotilapia gibberosa, tropical fish anatomy, frontosa, mpimbwe frontosa


Fish Anatomy may be one of the things that you thought you would never have to learn about. There are times in this hobby when you need to know the basics on the parts of a tropical fish. Most often one will need to know where the certain parts of a fish are when something goes wrong such as having a sick fish, or dealing with aggression in the tank.

So what are the important parts of the fish anatomy that you should know about?

As you can see from the diagram above, I have identified the major external parts of the fish that many sources will refer to for treatment or identification. Fish anatomy also includes the internal organs, but as traditional hobbyists, we really do not need to know the inner workings of the fish so I will not cover that at this point.

The Caudal Fin

The caudal fin or the “tail” can be one of the most beautiful fins on your freshwater tropical fish. This fin is the motor of the fish in the water. The caudal fin’s movements allow for the fish to swim throughout your aquarium tank.

The tail fin of a fish can vary depending on individual species. You have so many variations and each type of tail fin affects how the fish swims naturally.

Have you ever watched how a male guppy swims? Notice how it flutters throughout the water? This is because the male guppy has a very large and boisterous tail fin. If the tail fin were more compact the guppy would swim with a little more power and ease. 

Many species use their tail fin as a spawning or breeding aid. The sex of many species can be distinguished by the colors or length and shape of the tail fin. Swordtails and guppies are the two most common tropical fish that use this fin as a identifier between the sexes.

The caudal fin often is the first part of the fish that will show injury or abuse from aggression. When fish become aggressive towards one another, they chase each other and often take bites out of the tail fin.

The tail fin some cases is a good place to look for any signs of disease or bacterial infection of your tropical fish. Fin Rot and Ich are two common diseases/parasites that can affect the caudal fin.

The Pelvic Fins

The pelvic fins on a freshwater tropical fish are located on the bottom of the fish in front of the anal fin. These fish anatomy fin like all other fins will vary in appearance depending on the species you have. Tropical fish use their pelvic fins to change direction or just stabilize themselves in the water.

There are several species that may use the pelvic fin as an aid in defending themselves, or in breeding. One species that comes to mind is the bristle nose or bushy nose pleco.

The Dorsal Fin

The dorsal fin is the fin that runs along the top of your aquarium fish. The dorsal fin actually plays a huge role in the fish’s swimming patterns. This part of the fish anatomy allows for the fish to swim in straight and not off balance in the water.

Anyone that has ever gone fishing and had to take the fish off of the hook will tell you that the dorsal fin can prick you if your are not careful. This is true for some of the larger tropical fish species we keep in our home aquarium tanks.

The dorsal fin along with the other fins I am discussing plays a huge role in the survival of our tropical fish. If a fish is sick or injured, and their fins are not 100%, the fish will struggle and have to work harder to swim.

If a fish has to work harder to swim, this means the fish has to work harder at everything! Fish must be able to swim fast and precisely to compete for food and territory. A fish that has trouble swimming will wear itself out and may even get so weak that it dies.

The Pectoral Fins

The pectoral fins are located under the gills towards the bottom of the fish. Each fish has one pectoral fin on each side of their body. The pectoral fins help the fish swim, backup, and hover beautifully in the open water. The pectoral fins are like the blades on a helicopter. They are always moving so that the fish can remain stable in the water.

The pectoral fins are susceptible to injury and illness just as the caudal or tail. The pectoral fins are often picked at and bitten off during fighting. If you have notice a fin missing or injured, be aware that there is some major aggression in your tank. Also, fin rot and ich can be spotted here often also.

The Anal Fin

The anal fin is exactly where you would think a fin named this would be…. Near the anal cavity. The anal fin is in front of the caudal fin and behind the pelvic fin. This part of the fish anatomy helps your fish swim straight throughout the water. Some fish have very beautiful anal fins that grow quiet large.

Many cichlids and other egg laying tropical fish have what we call and eggspot on their anal fin. The eggspot is actually on the male of the species and it serves a very important role in spawning. The eggspot is a small circle that resembles and egg on the anal fin. During spawning, the female deposits her eggs on the substrate and the male swims over them fertilizing them with his sperm. The female then goes behind him and picks the eggs up in her mouth for brooding. During this process, the female will actually swim up under the male and open her mouth towards the eggspot as if she things this is another one of her eggs. When this happens, the male deposits more sperm into the water column and the female ends up fertilizing the entire batch in her mouth during this process.

Fish Senses

Other than the basic fish anatomy, have you ever asked yourself….

“Do tropical fish have senses?”

If you would like to learn more about your pet fish’s ability to hear, smell, see, and taste, please read: Fish Senses.


Related posts: