color genetics

The Basics of Betta Fish Color Genetics

One of the main attractions of keeping betta fish is the incredible diversity of colors and forms that you can find in these glorious jewels of nature.

Many betta hobbyists move on to try their hand at breeding bettas from their own stock. In some cases, completely new strains of betta have been created by amateur enthusiasts, experimenting with crossbreeding fish in their collections.

Before you dive into the wonderful world of breeding bettas, you should know something about the basic color genetics of this fascinating fish. 

Read on to find out more!

The color layers of betta fish

There are up to 26,000 genetic combinations that create the myriad colors and patterns that you find in captive betta fish.

Betta coloration is based on the color pigmentation of the various cells that form layers within the fish’s skin. There are essentially four layers of color cells in the betta’s skin:

1. Iridescent Layer (Top layer)
2. Black Layer
3. Red Layer
4. Yellow Layer (Bottom layer)

Often, these layers are mixed up with the color pigmentation of wild bettas, which is slightly different:

1. Iridescent Layer (Top layer)
2. Red Layer
3. Black Layer
4. Yellow Layer (Bottom layer)

The black coloration is regarded as the wild betta’s base color. Iridescent green or blue is the densest at the top layer, while the yellow color is the least dense and forms the bottom layer. That yellow coloration is so much less dense than the other colors and is, by definition, a lighter color, so it can be safely ignored when discussing wild betta colors.

Captive betta colors

Each of the color layers in captive bettas has its own genetic code or series of genes that determine the color of the fish. The gene either decreases or increases in pigment, depending on the layers, and it also controls where each color is distributed. So, your betta fish’s color is determined by the color pigments in his color cells, which are found within the layers of your fishy friend’s skin.

These color traits are known as phenotypes and are what is presented visually. The genes that comprise the traits are called genotypes. Genotypes contain the information that proteins need to catalyze the reactions that produce the color pigment that you see.

Betta color genetics can be extremely complicated, and when you’re playing around with breeding fish outside of an established strain, you can get some big surprises!

Color Layers Explained

Now, let’s take a look at each of the color layers in more detail.

Iridescent layer (top layer)

The top layer or blue layer controls the quantity of blue pigment in the fish.

Guanophores (green/blue cells), also known as iridophores, contain the following traits:

  • Blue/green (royal blue, green, and steel blue)
  • Spread iridocytes (turquoise blue)
  • Non-blue (total absence of blue)

The blue/green color is represented by the B1 gene. B1 can create three different colors:

  1. Steel-blue iridescents, giving a steel blue fish–> b1b1
  2. Royal blue iridescents, giving a royal blue fish–> B1b1
  3. Green iridescents, giving a green fish–> B1B1

So, you can see that if you crossbreed a pair of steel blue bettas (b1b1 x b1b1), you will get 100% steel blue offspring. Similarly, when crossbreeding a pair of green bettas (B1B1), the spawn will all be green. However, if you crossbreed a pair of royal blue bettas (B1b1 x B1b1), the fry will be 50% royal blue, 25% green, and 25% steel blue.

You should also know that if there is a large amount of black pigment under the iridescent layer, the colors will all appear much richer and darker. The absence of black generates a more pastel appearance.

Spread Iridocytes?

Spread iridocytes are genes that give the betta fish their glorious metallic reflective qualities, producing stunning colors such as turquoise. The term “iridocytes” refers to the crystals that create the iridescence that create the blue to green shades. 

The term “spread iridocytes” identifies the genetic SiSi gene, which increases the amount of iridescence in betta fish. Although researchers don’t yet entirely understand this gene, they do know the sisi combination creates much-reduced iridescence. Given the wide variance in the amount of iridescence that is seen across various betta specimens, it is thought likely that Sisi may create an intermediate level of iridescence or that there could be more than one pair of genes involved.

The non-blue gene occurs in bettas that have no blue layer, although no identified gene eliminates the blue layer completely. However, several betta breeders have produced fish that do not show any signs of blue at all. 

In the case of a b1b1 combined with a sisi, the blue layer may be extremely limited, creating only a very moderate blue glow to the point where it might not be recognized as an actual blue. When you add the Cambodian to this and the blond/bright trait in yellow and white fish, you might find that the compounding effect limits the blue layer. However, there may still be an as yet undiscovered gene that creates the no-blue.

Black layer

Black cells called melanophores contain the following traits:

  • Cambodian (cream body, red fins)
  • Blonde/bright (bright “cherry” color)
  • Melano (black bettas)

The above three genes will directly affect the black layer.

In Cambodian bettas, you’ll find a wide variety of fish, including those with the traditional flesh-colored body and red fins. The Cambodian gene (cc) is a double recessive. The presence of the cc gene eliminates all dark pigment. Some of the newer Cambodian forms have white, green, blue, and even purple fins.

The blonde/bright gene (bb) is also a double recessive. The effect of the bb gene is to limit the black pigment and is best observed in red bettas where its presence creates a bright red fish. The absence of the bb gene creates a maroon-colored fish of much darker color. The bb gene also comes into play with iridescent bettas, making them appear much more pastel in color. 

The melano gene mm is a double recessive. The mm gene increases the black pigmentation in a betta, meaning that you will finish up with a black fish. Unfortunately, somewhere along the line, the mm gene renders most melano females infertile. So, a breeder would need to cross their black male betta with a black lace or blue female. 

Black lace bettas have beautiful, almost transparent fins. Also, black lace females are fertile, so a pure black lace pair will always produce black offspring.

Red layer

The red cells are called erythrophores and contain the following traits:

  • Extended red (red covering the betta’s whole body and fins)
  • Reduced red (red covering only the fins, body dark in color, green or blue)
  • Non-red (total absence of red)
  • Variegated finnage (the butterfly effect)

These four genes determine the amount of red in the fish.

The extended red gene, R, controls the distribution and intensity of red color in a betta fish. Extended red genes mean that the red color will cover the entire body and fins of the fish, which is the most desirable coloration. The R gene is similar to the Si gene, as there are various degrees of red. Bettas can have less red distribution (rr) or more (RR).

Reduced red betta fish have a darker body color (black, green, or blue) with red fins. No gene has been identified that causes a reduction in the red pigmentation.

The non-red gene is double recessive nrnr and does not show any red pigment. Most breeders believe that the non-red gene modifies the pigmentation from red to yellow, which is very slightly evident.

The gene for variegated fins controls the red in the fins and creates the butterfly effect. Dr. Gene Lucas refers to that gene as Vf, and it is this gene that controls the variegation of red in the fins. The distribution of red pigment in the fins can occur in various patterns and degrees of intensity.

Yellow layer (bottom layer)

The yellow color cells are called Xanthophores. The Xanthophores do not have a red, black, or iridescent (blue) layer. 

As yet, there have been no genes identified that control the yellow layer of pigment. That means that a yellow betta has Cambodian (non-black) pigments in the black layer, non-red pigmentation in the red layer, and non-blue pigments in the iridescent layer.

That said, some breeders think that yellow could be related to the opaque gene.

Final thoughts

As you can see, the science of betta fish is complex but fascinating, and it’s that that makes breeding and crossbreeding these beautiful fish such an absorbing and addictive hobby.

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