Betta
The Siamese fighting fish (Betta splendens), commonly known as the betta, is a freshwater fish native to Southeast Asia, namely Cambodia, Laos, Myanmar, Malaysia, Indonesia, Thailand, and Vietnam. It is one of 73 species of the genus Betta, but the only one eponymously called "betta", owing to its global popularity as a pet; Betta splendens are among the most popular aquarium fish in the world, due to their diverse and colorful morphology and relatively low maintenance.
Siamese fighting fish are endemic to the central plain of Thailand, where they were first domesticated at least 1,000 years ago, among the longest of any fish. They were initially bred for aggression and subject to gambling matches akin to cockfighting. Bettas became known outside Thailand through King Rama III (1788–1851), who is said to have given some to Theodore Cantor, a Danish physician, zoologist, and botanist. They first appeared in the West in the late 19th century, and within decades became popular as ornamental fish. B. splendens long history of selective breeding has produced a wide variety of coloration and finnage, earning it the moniker, "designer fish of the aquatic world".
Bettas are well known for being highly territorial, with males prone to attacking each other if housed in the same tank; without a means of escape, this will usually result in the death of one or both fish. Female bettas can also become territorial towards one another in confined spaces. Bettas are exceptionally tolerant of low oxygen levels and poor water quality, owing to their special labyrinth organ, a characteristic unique to the suborder Anabantoidei that allows for the intake of surface air.
In addition to its worldwide popularity, the Siamese fighting fish is the national aquatic animal of Thailand, which remains the primary breeder and exporter of bettas for the global aquarium market. Despite their abundance as pets, B. splendens is listed as "vulnerable" by the IUCN, due to increasing pollution and habitat destruction.
Outside Southeast Asia, the name "betta" is used specifically to describe B. splendens, despite the term scientifically applying to the entire genus, which includes B. splendens and at least 72 other species. Betta splendens is more accurately called by its scientific name or "Siamese fighting fish" to avoid confusion with the other members of the genus.
English-speakers often pronounce betta as "bay-tuh", after the second letter in the Greek alphabet. However, it is believed the name is derived from the Malay word ikan betta, with ikan meaning "fish" and bettah referring to an ancient warrior tribe, which is pronounced "bet-tah". Alternative sources suggests the name Betta splendens is formed from two languages, consisting of Malay for "enduring fish" and the Latin word for shining.
Another vernacular name for Siamese fighting fish is plakat, often applied to the short-finned ornamental strains, which is derived from the Thai word pla kat (Thai: ปลากัด), which literally means "biting fish". This name is used in Thailand for all members of the Betta genus, which share similar aggressive tendencies, rather than for any specific strain of the Siamese fighting fish. Thus, the term "fighting fish" is used to generalise all Betta species besides the Siamese fighting fish.
Siamese fighting fish were originally given the scientific name Macropodus pugnax in 1849—literally "aggressive fish with big feet", likely in reference to their elongated pelvic fins. In 1897 they were identified with the genus Betta and became known as Betta pugnax, referring to their aggressiveness. In 1909, the species was finally renamed Betta splendens upon the discovery that an existing species was already named pugnax.
B. splendens usually grows to a length of about 6–8 cm (2.4–3.1 in). Although aquarium specimens are widely known for their brilliant colours and large, flowing fins, the natural coloration of B. splendens is generally green, brown and grey, while the fins are short; wild fish exhibit strong colours only when agitated. In captivity, Siamese fighting fish have been selectively bred to display a vibrant array of colours and tail types.
Wild bettas exhibit strong colours only when agitated. Over the centuries, breeders have been able to make this coloration permanent, and a wide variety of hues breed true. Colours among captive bettas include red, orange, yellow, blue, steel blue, turquoise/green, black, pastel, opaque white, and multi-coloured. Recent evidence suggest blue-colored males may show higher levels of aggression than red-colored males. On the other hand, female bettas may have a preference for red-colored mates as opposed to their blue counterparts.
The betta's diverse colours are due to different layers of pigmentation in their skin. The layers, from deepest within to the outermost, consists of red, yellow, black, iridescent (blue and green), and metallic (not a colour itself, but reacts with the other colours). Any combination of these layers can be present, leading to a wide variety of colours within and among bettas.
The shades of blue, turquoise, and green are slightly iridescent, and can appear to change colour with different lighting conditions or viewing angles; this is because these colours (unlike black or red) are not due to pigments, but created through refraction within a layer of translucent guanine crystals. Breeders have also developed different colour patterns such as marble and butterfly, as well as metallic shades like copper, gold, or platinum, which were obtained by crossing B. splendens to other Betta species).
Some bettas will change colours throughout their lifetime, a process known as marbling, which is attributed to a transposon, in which a DNA sequence can change its position within a genome, thereby altering a cell. Koi bettas have mutated over time and in some case change colours or patterns throughout their lifetime (known as true Koi), due to the defective gene that causes marbling not being repaired in the color layers after some time.
Common colours:
Rarer colours:
Colour patterns:
According to Witte and Schmidt (1992), Betta splendens is native to Southeast Asia, including the northern Malay Peninsula, central and eastern Thailand, Kampuchea (Cambodia), and southern Vietnam. Based on Vidthayanon (2013), a Thai ichthyologist and senior researcher of biodiversity at WWF Thailand, the species is endemic to Thailand, from the Mae Khlong to Chao Phraya basins, the eastern slope of the Cardamom mountains (Cambodia), and from the Isthmus of Kra. Similarly, a report from Froese and Pauly (2019) identifies Betta splendens as native to Cambodia, Laos, Thailand, and Vietnam. They are also found throughout the neighbouring Malay Peninsula and in adjacent parts of Sumatra, likely due to human introduction.
Wherever they are found, Betta splendens generally inhabit shallow bodies of water with abundant vegetation, including marshes, floodplains, and paddy fields. The historic prevalence of rice farming across Southeast Asia, which provided an ideal habitat for bettas, led to their discovery and subsequent domestication by humans. The combination of shallow water and high air temperature causes gases to rapidly evaporate, leading to a significant deficit of oxygen in the betta's natural habitat. This environment likely led to the evolution of the lung-like labyrinth organ, which allows Siamese fighting fish—like all members of the suborder Anabantoidei—to breathe directly from the air. Subsequently, bettas can live and even thrive in harsher environments than other freshwater fish, which in turn leaves them with fewer natural predators and competitors. In the wild, bettas thrive at a fairly low population density of 1.7 individuals per square meter.
The tropical climate of the betta's natural habitat is characterized by sudden and extreme fluctuations in water availability, chemistry, and temperature. Water pH can range from slightly acidic (pH 6.9) to highly alkaline (pH 8.2), while air temperatures drop as low as 15 °C (59 °F) and rise as high as 40 °C (100 °F). Consequently, Siamese fighting fish are highly adaptable and durable, able to tolerate a variety of harsh or toxic environments; this accounts for their popularity as pets, as well as their ability to successfully colonize bodies of water all over the world.
Wild bettas prefer to live in bodies of water teeming with aquatic vegetation and surface foliage, such as fallen leaves and water lilies. The abundance of plants provides security from predators and a buffer between aggressive males, who coexist by claiming dense sections of plants as territory. Such vegetation also offers protection to females during spawning and to fry during their earliest and most vulnerable stages.
Betta splendens is naturally carnivorous, feeding on zooplankton, small crustaceans, and the larvae of aquatic insects such as mosquitoes, as well as insects that have fallen into the water and algae. Contrary to some marketing materials in the pet trade, bettas cannot subsist solely on vegetation or the roots of plants.
Bettas can be fed a varied diet of pellets, flakes, or frozen foods like brine shrimp, bloodworms, daphnia and many others. Due to their short digestive tracts—a characteristic of most carnivores—bettas have difficulty processing carbohydrates such as corn and wheat, which are commonly used as fillers in many commercial fish foods. Thus, regardless of the source, a proper betta diet should consist mostly of animal protein.
Bettas are susceptible to overfeeding, which can lead to obesity, constipation, swim bladder disease, and other health problems; excessive food may also pollute the water. It is generally advised to feed a betta at least once daily, with only the amount of food it can eat within 3–5 minutes; leftover food should be removed.
Some sources recommend that bettas undergo a "fast" for at least one day to allow food to be fully processed. Bettas can go up to two weeks without eating, and it is not uncommon for them to have no appetite for one or two days, especially following stressful episodes such as a water change or being introduced into a new tank.
If interested in a female, male bettas will flare their gills, spread their fins and twist their bodies in a dance-like performance. Receptive females will respond by darkening in color and developing vertical lines known as "breeding bars". Males build bubble nests of various sizes and thicknesses at the surface of the water, which interested females may examine. Most do this regularly even if there is no female present.
Plants or rocks that break the surface often form a base for bubble nests. During courtship, the male betta may exhibit aggressive behavior towards the female by acts of chasing or nipping at her fins. The act of spawning itself is called a "nuptial embrace", for the male wraps his body around the female; around 10–40 eggs are released during each embrace, until the female is exhausted of eggs. With each deposit of eggs, the male releases milt into the water, and fertilisation takes place externally. During and after spawning, the male uses his mouth to retrieve sinking eggs and place them in the bubble nest; during mating some females assist their partner, but more often will simply devour all the eggs she manages to catch. Once the female has released all of her eggs, she is chased away from the male's territory, as she will likely eat the eggs. If she is not removed from the tank, she will most likely be killed by the male.
The eggs remain in the male's care. He carefully keeps them in his bubble nest, making sure none fall to the bottom, repairing the bubble nest as needed. Incubation lasts for 24–36 hours; newly hatched larvae remain in the nest for the next two to three days until their yolk sacs are fully absorbed. Afterwards, the fry leave the nest and the free-swimming stage begins. In this first period of their lives, B. splendens fry are totally dependent on their gills; the labyrinth organ, which allows the species to breathe atmospheric oxygen, typically develops at three to six weeks of age, depending on the general growth rate, which can be highly variable. B. splendens can reach sexual maturity in as early as 4–5 months. Typically, the morphological differences between males and females can be noticed around two months after hatching. During development, betta fry can be fed either commercial artificial feeds, or live moving prey, which tends to be favored more. Examples of live feed for betta fry include baby brine shrimp, water fleas, and mosquito larvae. Although common fed to fish fry, boiled egg yolks are not preferred by the fish.
There has been much research in the courtship behaviour between male and female Siamese fighting fish. Studies generally focus on the aggressive behaviours of males during the courtship process. For example, one study found that when male fish are in the bubble nest phase, their aggression toward females is quite low. This is due to the males attempting to attract potential mates to their nest, so eggs can successfully be laid. It has also been found that in determining a suitable mate, females often "eavesdrop" on pairs of males that are fighting. When a female witnesses aggressive behaviour between males, she is more likely to be attracted to the male who won. In contrast, if a female did not "eavesdrop" on a fight between males, she will show no preference in mate choice. In regards to the males, the "loser" is more likely to attempt to court the fish who did not "eavesdrop", while the "winner" showed no preference between females who "eavesdropped" and those who did not.
One study considered the ways in which male Siamese fighting fish alter their behaviours during courtship when another male is present. During this experiment, a dummy female was placed in the tank. The researchers expected that males would conceal their courtship from intruders; instead, when another male fish was present, the male was more likely to engage in courtship behaviours with the dummy female fish. When no barriers were present, the males were more likely to engage in gill flaring at an intruder male fish. The researchers concluded that the male was attempting to court the female and communicate with its rival at the same time. These results indicate the importance of considering courtship behaviour, as the literature has suggested there are many factors that can dramatically affect the ways in which both male and females can act in courtship settings.
Due to their popularity, Siamese fighting fish are highly abundant in captivity. In the wild, betta habitats are threatened by chemical and agricultural run off, in addition to the contamination of human medication residue into aquatic ecosystems from the sewage system. Such contamination can also alter the reproductive behavior of the species by decreasing hatch rate and increasing the likelihood of fathers eating their own eggs. Due to the expansion of palm oil plantation in Southeast Asia, wild bettas are also facing habitat loss. The primary threats are habitat destruction and pollution, caused by urban and agricultural development across central Thailand. Wild specimens are categorized by the IUCN as vulnerable, indicating the species is likely to become endangered without conservation efforts.
B. splendens are known for their intense aggression, which has resulted from intense selective pressures imposed upon them from many generations of artificial selection. Fighting strains of B. splendens have been bred for aggression for over six centuries due to the culture surrounding fighting betta fish and betting money on the results. This has genetically differentiated them from their wild-type counterparts – fighting strains of B. splendens have been shown to be significantly more aggressive than wild bettas, and in addition show differential responses in cortisol production in new environments.
The extreme genetically driven aggression in fighting strains of B. splendens and their differences from the still-observable wild-type makes them an excellent candidate for a model organism through which to study the genetic basis for aggression.
At present, use of the betta fish as a model organism for studying aggression is in its beginning phases. Little is known about the genetic basis of aggression in betas, though differential degrees of aggression have been observed in different domesticated betta populations.
Betta splendens first entered the Western aquarium trade in the late 19th century; the earliest known arrival is 1874 in France, when French aquaria expert and ichthyologist Pierre Carbonnier began importing and breeding several specimens. In 1896, German tropical fish expert Paul Matte brought the first specimens into Germany from Moscow, most likely from the strain developed by Carbonnier. This indicates bettas were already somewhat established in France and Russia by the turn of the 20th century. Fighting fish were also present in Australia by 1904, based on an article written by British-born zoologist Edgar Ravenswood Waite and published by the Australian Museum in Sydney. Waite indicates that Australian specimens were brought from Penang, Malaysia, near the border with Thailand. He also makes reference to two articles about "fighting fish" published by Carbonnier in 1874 and 1881. Bettas may have first entered the United States in 1910, via importers in California; there is also evidence they were imported in 1927 from Cambodia.
While it is unclear when bettas became popular in the aquarium trade, the early 20th century marked the first known departure from centuries of breeding bettas for aggression, to instead selecting for colour, finnage, and overall beauty for ornamental purposes. In 1927, an article was published in Germany describing the long, flowing fins of the "veiltail" breed, which indicates an emphasis on aesthetic beauty. In the 1950s, an American breeder created a larger and longer-finned veiltail, while around 1960, Indian breeders discovered a genetic mutation that allowed for two caudal fins, producing the "doubletail" variety. Within that decade, a German breeder created the "deltatail" characterised by its broader, triangular fins.
In 1967, a group of betta breeders formed the International Betta Congress (IBC), the first formal interest group dedicated to Siamese fighting fish. The IBC aimed to breed varieties that would be healthier and more symmetrical in fins and body shape, with an emphasis on animal welfare.
Despite frequently being displayed and sold in small containers in the pet trade, bettas do best in larger environments; while they can survive in cups, bowls, and other confined spaces, they will be much happier, healthier, and longer-lived in a larger aquarium. Although some betta enthusiasts claim there is a minimum tank size, determining a strict baseline is somewhat arbitrary and subject to debate. The general consensus is that the ideal tank should be no less than 19 litres (5 US gallons), although a novice owner will often find a larger aquarium easier to maintain if they can find the space for it.
Although male bettas are solitary and aggressive towards one another, they can generally cohabit with many types of fish and invertebrates if there is adequate space and hiding places. However, compatibility varies based on the temperament of the individual betta, and it is advised to carefully supervise the betta's interaction with other fish. Tankmates must be tropical, communal, nonterritorial, and not have a similar body type or long flowing fins; coldwater fish like goldfish have incompatible temperature requirements, while aggressive and predatory fish are likely to nip at the betta's fins or erode their slime coat. Species that shoal, such as tetras and danios, are considered most ideal, since they usually keep to themselves and can endure the territorial nature of bettas with their numbers. Brightly coloured fish with large fins, such as male guppies, should be avoided, as they may invite fin nipping by the male betta. Potential tankmates should usually be added before the male betta so they can establish their respective territories beforehand, rather than compete with the betta.
Female bettas are less aggressive and territorial than males, and thus can live with a greater variety of fish; for example, brightly coloured or large-finned fish will not usually disturb a female. Generally, female fighting fish can also tolerate larger or more numerous tankmates than males. However, like male bettas, a female's tolerance of other fish will vary by individual temperament.
It is not recommended to keep male and female bettas together, except temporarily for breeding purposes, which should always be undertaken with caution and supervision.
