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Betta Fish Marbling (Color-Changing Gene): Everything You Need to Know

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By Lindsey Stanton

male galaxy koi betta

Betta fish are a real feast for the eyes: their shimmering colors and sail-shaped fin make them a much-desired pet fish. They come in an array of colors and shapes, determined by certain specific genes. The marble gene is of particular interest to aquarists because of the color change it induces in the betta. This change is fascinating to watch, as the betta gradually loses its color on its fins and body and subsequently takes on a whole new costume. Find out everything you need to know about betta fish marbling in this handy little guide!

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Where Do the Colors Come from in Betta Fish?

The different colors of Betta splendens are due to two different phenomena:

  • The presence of three pigments: lutein (yellow), melanin (black), and erythropterin (red)
  • The scattering of light through small guanine crystals: this allows light to be dispersed, resulting in the iridescent color (royal blue, steel-blue, and turquoise/green).

Each pigment is contained in a cell type: xanthophores for yellow pigments, melanophores for black, and erythrophores for red. For iridescent layers, the cells responsible for them are called iridocytes.

According to several theories, the colors of a betta are arranged in layers. However, there are still unknowns on how these layers are arranged or, scientifically speaking, on the color genetics of Bettas splendens giving the various phenotypes that we know.

  • Note: Do not confuse genotype with phenotype. The genotype is the set of genetic characteristics of a living being. The phenotype is the expression of the genotype, which means all the observable traits (such as colors).

The most plausible theory, although it arguably contains errors, is H.M. Wallbrunn’s Four Layers Theory: it says that the colors in Betta splendens have been organized into four successive layers:

  • Yellow (the deepest layer)
  • Black
  • Red
  • Iridescent (the most superficial layer)

Each layer has its own mutations due to a gene made up of two alleles, a dominant (expressed by a capital letter) and a recessive (described by the same letter but lowercase).

Therefore, the color diversity in the domestic Betta splendens corresponds to the different possible allelic combinations for all the genes of each of the four-color layers and the presence or not of the marble gene (MBmb).

Plakat Betta in aquarium
Image Credit: Eyeshot Creative Studio, Shutterstock

What Is the Marble Gene?

Marbling is when a betta changes color: it can be red, blue, purple, or white, or a combination of both. Marble is also the name of a jumping gene, or transposon: a DNA sequence that can change its position in the fish genome. As a result, marble bettas often have colored patches (or areas without pigment) all over their body and fins.

However, the betta’s color will be unstable due to this same jumping gene: indeed, throughout the life of the fish, the gene will be able to activate or deactivate the pigment.

This explains why the betta with this gene will not keep the same color patterns all its life. Besides, the jumping gene can affect almost any color pigment, creating a rainbow of possibilities.

betta fish on black background
Image Credit: nicefishes, Pixabay

What are the Origins of the Marble Gene?

This particular strain came about entirely by accident. Orville Gully, a prisoner held at Indiana State Prison, was looking to create butterfly bettas. To do this, he crossed black bettas with white bettas but instead obtained marble fish (however, the story does not say why Gully was allowed to breed bettas in his small cell!).

He later sent his baby bettas to the International Betta Congress (IBC), which caught the eye of Walt Maurus, a betta fanatic and prolific author. So Maurus and other betta lovers started breeding this new strain of fish.

Today, this marble gene applies to all color layers except the iridescent layer.

Meet the Jumping Gene

In 1985, Steve Saunders proposed a theory that a “jumping gene” (or transposons) was associated with the marble gene. Dr. Barbara McClintock has demonstrated the existence of transposable elements during studies on Indian corn, which makes Saunders’ theory quite plausible.

Indeed, Dr. McClintock studied the mechanisms responsible for the color variations appearing on Indian corn kernels.

Saunders also gave a summary of the characteristics of the strains of marble bettas:
  • In a spawning of marble bettas, you always get dark-solid, light-solid, and marble bettas.
  • Spawning between two dark single-colored bettas or two light single-colored bettas from a marble strain will result in either dark or light unicolored bettas, marble bettas, and variegated fin bettas.
  • Suppose a marble betta is crossed with a single-colored betta from a pure single-colored line. In that case, it will be challenging to eliminate the marble phenotype of the single-colored strain subsequently. Crosses between two unicolored will always result in at least a few marble bettas.
  • Crossing a marble betta with a betta without this specific gene may result in marble bettas of the parent’s color without the marble gene.
sick betta fish
Image Credit: yin8003211, Pixabay

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Final Thoughts

To sum up, betta fish marbling results from a transposable element, commonly known as the “jumping gene”. This gene can change its position within the fish’s genome, resulting in an ever-changing color pattern. This means that if your pretty betta fish has this gene, it will probably experience various color changes throughout its life. So, if you’ve been wowed by the gorgeous turquoise color of your betta, don’t be disappointed if it turns red and white a few weeks later!


Featured Image Credit: Ron Kuenitz, Shutterstock

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