Betta Fish Anatomy Explained

We gaze at our Bettas with pride and amusement. We see his beautiful flowing fins and gorgeous colors and laugh when we experience his curiosity and spunky personality. On occasion, we also examine him using a closer eye to detail to ensure he is healthy. 

But do we really know what we are looking at?

In this post, we will take an in-depth look at the Betta fish anatomy, so you can know your aquatic friend inside and out!

male betta fish


Betta Fish Anatomy Explained – The Outside View

The bold, beautiful Betta is a sight to behold! Let’s discover everything there is to know about our Betta Fish outside view. 


Betta’s are considered “streamline” and are designed to effortlessly swim through densely planted ponds and rice paddies.

Males measure from 2.4 to 3.1 inches long while females are around 2.25 inches long. 


These beautiful “appendages” allow the Betta to maneuver through the water while remaining stable and balanced. There are 5 different fins;

  1. Dorsal Fin – a single fin located on top of the Betta (and slightly to the back) is used for turning and stabilization. It is also made up of several vein-like branches of cartilage. 
  2. Pectoral Fin – located just behind the gills, these small fins (sometimes referred to as ears) are constantly in motion as the Betta swims along. They can vary in size and color depending on the age and breed of the Betta fish.
  3. Caudal Fin – also called the tail fin is located at the back of the Betta. It is used for steering and propelling the fish forward.  
  4. Ventral/Pelvic Fins – located below the pectoral fin, they flare out and also assist in movement such as ascending, descending, stopping, and sudden turns. 
  5. Anal Fin – used for stabilizing the Betta, it runs on the underside of the fish getting larger toward the back. 

Of course, the fins vary in size on the Betta species – males being long and flowing while the females remain short and serviceable. 


Like all fish, the Betta has scales that provide both protection of the fish body and aid in swimming. 

If you have ever touched or had to handle your Betta, you may have noted it was slimy. What you felt was actually a mucus layer that keeps parasites, bacteria, and some diseases at bay. 

Pro Tip: Only handle your Betta if absolutely necessary, as you can damage the mucus layer, leaving your fish vulnerable to parasites and disease. 

Interestingly, the scales of the Betta fish are transparent. Those vibrant colors are actually coming from Betta’s skin below. 


If you were to closely examine a Betta’s mouth, you would notice that the lower portion juts out ever so slightly. This upturned mouth allows the fish to capture surface prey such as small insects and mosquito larvae. This unique feature also allows the male Betta to gently slurp up the female’s eggs from the bottom of the tank, carry them to the top of the tank and “spit” them into the bubble nest, safe and undamaged.

If you could somehow peer into your Betta’s mouth, you would also discover many tiny sharp teeth on its lower jaw. These are by no means dangerous to us humans but to another male Betta? Well, they are called “fighting fish” for a reason. When those teeth aren’t being used to defend their territory, they are breaking down their food. 

Interestingly, the power of the Betta’s jaws (proportionally to their body) is considered more forceful than the power of a Great White Shark!


The gills of the Betta work the same as any other set of gills – water enters through the mouth and across the gills where the blood flowing through tiny capillaries extract (or absorb) the oxygen in the water. 


The operculum acts as a protective shield for the Betta’s fragile gills. It also covers the membrane or beard on the male of the species. The operculum comes into play when the male is trying to appear bigger, he will flare his gill coverings and extend his beard to show who is boss. 


Betta’s small beady eyes are there for vision (obviously). Scientifically, this species of fish is considered monocular (the eyes are on the opposite sides of the head) and they both produce a different image. 

This species has very good eyesight which is why they can focus on other male Bettas or their own reflection (resulting in flaring). They can see well up to a foot away and navigate their surroundings in full color. However, Bettas don’t have eyelids and therefore cannot blink as we do. 

Their eyesight also lends itself to Betta’s curious nature. Try running your finger alongside their tank or adding a new decoration, plant, or toy. It won’t be long before your pet is checking it out. 

Betta Fish Anatomy Explained – The Inside View

Have you ever wondered what’s going on inside your BFF (best fishy friend)? Let’s examine and explain those innards.

Labyrinth Organ  

The Betta is one of 70 species of fish that possess a labyrinth organ. This specialized cavity contains several maze-like compartments of lamellae (thin bony plates) that are covered in extremely thin membranes which allow oxygen to pass through, The blood found in these membranes then absorbs the oxygen in the water and carries it throughout the Betta’s body. 

The labyrinth organ comes in handy for, not only, gulping air from the surface of their environment, but for also making bubble nests (something the male does in preparation and storing of the eggs). 

Gill Arch

This specialized bony support area is where air passes from the esophagus, through the gill cavity and the labyrinth for oxygen  Here there are also gill filaments and gill rakers that are attached to the gill arch. 


The esophagus of the Betta is connected to the mouth. It is responsible for passing food, air, and water into the body to aid the other organs.


It’s good to note that the size of Betta’s stomach is about the same size as one of their eyeballs. For this reason, you do not want to overfeed your fish as it can lead to constipation and swim bladder disorders.

Pro Tip: It is recommended that you put your Betta on a fast one day a week. This allows all the food to work its way through your Betta’s system.

Swim Bladder  

The swim bladder of the Betta comprises much of its internal body. It resembles an elongated balloon and runs along the spine, growing with the fish. 

This important internal compartment is responsible for keeping your fish afloat. They do this by filling the swim blade with gas to control their buoyancy. If the swim blade becomes diseased (by overfeeding, constipation, or bloating) it will be difficult for your fish to swim or navigate to the top or bottom of the tank. 

Testes (Male)

Unlike males of the animal kingdom, the testes of the male Betta fish are located inside the body between his bladder and swim bladder. They are used in reproduction, of course.

Ovipositor Tube (Female)

This white dot is located at the base of the ventral fins. During mating, the eggs are released from the ovipositor. 


The small hole (anus) on the Betta fish is located in front of their anal fin. This is where digested food will be eliminated from the body. 


The kidney is located on top of the swim bladder and intestine of the Betta fish. It filters out impurities in the blood and is oftentimes the underlying cause of dropsy. 


When the broken down food leaves the stomach it enters into the intestine for further breaking down. Here the nutrients (protein and vitamins) are absorbed and used to fuel the fish. 


As with all living creatures, the heart of the Betta is responsible for pumping blood throughout its body and maintaining its blood pressure. The heart is located near the ventral fins of this species. 


The bladder of the Betta is located between the testes and the anus. The bladder holds the waste products that the kidney has filtered out of the blood. 


The liver is located in front of the intestine of the Betta fish. It helps support digestion and also storage within the body. The liver also secretes bile (enzymes) to enable the process of food through the stomach and into the intestine. 

Difference Between Male and Female Bettas

It is very difficult to tell the difference between male and female Bettas at the fry stage. However, at around the age of 8 weeks, Betta will begin to show gender differences.

Males have:

  • Thicker bodies
  • Longer fins (tail, anal, and dorsal fins make them appear larger)
  • More vibrant colors
  • Operculum (beard) will begin to appear

Females have:

  • Thinner bodies
  • Duller hues
  • Small beard (does not extend beyond gill covers)
  • An ovipositor tube 

Final Thoughts on Anatomy

Whether your Betta is just a pet or you are interested in all things anatomical, knowing the inside and outside of your Siamese Fighting Fish is beneficial. Not only will you be fascinated by the workings of this beautiful creature, but you will be able to quickly identify when your fish has an illness or issue.