A century of selective breeding has made <em>Betta splendens</em> into long-finned, vibrantly colored fish; the happiness of this blue and red <em>Betta</em> is apparent by its "bubble nest" in the top right.

A century of selective breeding has made Betta splendens into long-finned, vibrantly colored fish; the happiness of this blue and red Betta is apparent by its "bubble nest" in the top right.

The Splendid Betta

A Pet Fish that Breathes Air

With long-flowing fins in a dizzying assortment of styles and bright colors, and the ability to survive in a small bowl of water, it’s little wonder that the Betta, scientifically known as Betta splendens, has become such a popular pet fish. So how did the Betta gain these two distinctive qualities that have made them the popular pets they are today?

It turns out that their ability to survive in small, unfiltered bowls of water is actually a very ancient trait, while their long, colorful fins are a much more recent development.

The origin of the Betta’s ability to survive in shallow, dirty waters can be traced back to when the first lungs evolved, some 416 to 360 million years ago during the Devonian Era, also known as the “Age of Fish.” Fossils and geologic records have helped us understand that during this time, Earth had frequent droughts and consequently many fish lived in shallow seas and lakes. Some fish developed unique nostrils that were used to smell the air, but not breathe it. This group is known as Choanichthyes.

Although their nostrils were originally used for smelling, over time the fish became able to do more than just smell the air they took in. Part of the intestines in these fish became rich in blood vessels (highly vascularized). Because blood vessels are used for gas exchange and transporting oxygen to organs, when this vascularized tissue was exposed to air the fish could take in airborne oxygen and get rid of carbon dioxide waste. Although the fish already had gills that could take in oxygen and release carbon dioxide through the water, this secondary system was a great advantage for these fish. Fish with increasingly larger areas of this vascularized tissue in their intestines were selected for, over countless generations, said tissue eventually becoming lungs. The Devonian Era also saw the development of the first creatures with legs, which, coupled with their new lungs, allowed them to move from the water to the land.

However, in some species, the vascularized tissue did not fully develop into lungs, but into another unique organ, called a labyrinth, which is present in many fish today, including the Betta. The labyrinth is located just above the gills and contains many folds of highly vascularized skin tissues, allowing these fish to gulp air and retain it in the cavity, all the while absorbing oxygen from the captured air. Because these amazing fish have two gas exchange systems, while most fish only have one (gills), they can survive in very low-oxygen waters.

After the Cretaceous-Tertiary extinction event, which saw the demise of the dinosaurs, the group of fish species equipped with a labyrinth organ (the anabantoids) started evolving into different branches. Today, the labyrinth fish live in freshwaters in Asia and Africa and include paradise fish, gouramis, and Bettas (which are in the gourami family). Members of the amazing genus Anabas have such a highly developed labyrinth that they can survive in dried mud for several hours!

Betta splendens is common in its native lands of Thailand and Malaysia, where it is a dullish yellow with relatively short fins, a stark contrast to what is seen in pet stores today. Using its labyrinth organ, it survives in small amounts of low-oxygen water, such as puddles, drainage ditches, and rice paddies. Any Betta owner probably knows they are quite the avid jumpers, and in the wild they can jump and squirm to get from one puddle to another.

B. splendens originally caught attention not only because of its ability to survive in small containers of water, but also because it can be quite a fierce fighter. When put together in a small space, two male Bettas will fight, flaring their fins and nipping at each other. Around 150 years ago, gambling on Betta fights was quite common in Thailand, and bets are said to have included not only money and belongings but also children. These fights earned Bettas the moniker Siamese Fighting Fish (as Thailand at the time was called Siam). However, the fish were not fought to the death; the fights were about bravery and promptly ended when one fish backed down in submission. Usually a fish would only be fought once or twice before retiring as a spoiled pet for life. (In the wild, fights between males are usually not to the death either, unless there is very limited space.)

In 1840, the King of Siam gave a pair of breeding B. splendens to Dr. Theodore Cantor, a Danish biologist working with the British East India Company. Cantor studied the fish for years and introduced them to Europe in a scientific paper he published in 1849. However, he misclassified the fish, calling them Macropodus pugnax (the Macropodus genus includes the closely related paradise fish). This was corrected in 1909 by the British ichthyologist Dr. Tate Regan, who suggested the name Betta splendens. (The fish is said to have been named after an old Asian warrior clan named “Bettah,” though accounts differ.) In 1896, several breeding pairs were brought to Germany, and from there B. splendens spread through parts of Europe. B. splendens made its way to the United States in 1910, imported by American businessman and fish enthusiast Frank Locke.

Locke recognized one of the first naturally occurring color mutations in B. splendens; one of his fish had red color on its fins. Betta breeders, both hobbyists and professionals, began selecting for vibrant colors and long fins over many generations, creating an astonishing array of Bettas. Today, B. splendens can be found in many shades of yellow, white, blue, red, and black, as well as in bi-color and patterned forms. A large variety of tail and fin styles also exist, perhaps the most common “fancy” Betta style being the crowntail, in which all fins are heavily frilled. Even variations in body size have developed; “giant Bettas” (labeled Plakat Yak) were created around ten years ago by careful breeding. Most of the colorful, long-finned Bettas in pet stores are males; the females are usually duller in color and have much shorter fins.

Their colorful diversity and natural hardiness have contributed to Bettas being popular pets. While a Betta can survive in a very small bowl of water, this is not ideal; a Betta should have at least one gallon, with some sources recommending up to ten gallons, of shallow water (so they can easily surface for air). Because Bettas are kept in water without a filter system, weekly water changes are recommended to prevent the waste (e.g. ammonia and nitrates) from building up to toxic levels. Also, since Bettas are tropical fish, they prefer warm water, generally around 76 to 80 degrees Fahrenheit.

Aside from giving it room to stretch its fins, there are many ways to “treat” a pet Betta. Although male Bettas cannot be kept together, they can be kept with other fish in a community tank, which may be quite stimulating for them, although checking species-compatibility is always essential before putting them in the same tank. Plants can also provide enrichment for the fish, although plants are not food for Bettas (despite many being sold in vases with roots dangling in the water). Tasty, round food pellets are sold just for the carnivorous Betta, although they also enjoy live food (e.g. blood worms or brine shrimp). It’s often easy to see whether a male B. splendens is happy by the presence of a “bubble nest” in a corner at the top of his tank. With the proper research, Bettas can even be easy and fun to breed.

So, when in the market for a beautiful, feisty fish to brighten up some workspace, consider the unique and splendid Betta. Contrary to popular belief, the Betta is actually the only widely sold fish that can thrive in an unfiltered aquarium; goldfish should not be kept in bowls as they are very dirty fish and cannot breathe air. Indeed, the amazing and ancient labyrinth organ makes the Betta quite suitable for life on a desk.

For more on B. splendens, see Marcus Song’s Caring for Betta Fish, Robert J. Goldstein’s Anabantoids: Gouramis and Related Fishes, the “International Betta Congress,” Wikipedia’s “Betta,” Wikipedia’s “Siamese Fighting Fish,” Wikipedia’s “Anabantoidei, Rena Sherwood’s “The History of the Betta,” and Elizabeth Cristopher’s “Fish Fighting – From the King of Siam to America.”

Biology Bytes author Teisha Rowland is a science writer, blogger at All Things Stem Cell, and graduate student in molecular, cellular, and developmental biology at UCSB, where she studies stem cells. Send any ideas for future columns to her at

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