Siamese fighting fish display complex behavioural patterns and social interactions, which vary among individual specimens. Research indicates they are capable of
associative learning, in which they adopt a consistent response following exposure to new stimuli. Males and females flare or puff out their
gill covers (opercula) to appear more impressive, either to intimidate other rivals or as an act of
courtship. Flaring also occurs when they are intimidated by movement or a change of scene in their environments. In captivity, bettas can be seen flaring at their own reflection because they do not pass the
mirror test for self-recognition. Both sexes display pale horizontal bars if stressed or frightened. However, such colour changes, common in females of any age, are rare in mature males due to their intensity of colour. Females often flare at other females, especially when setting up a
pecking order.
Flirting fish behave similarly, with vertical instead of horizontal stripes indicating a willingness and readiness to breed.
Betta splendens enjoy a decorated tank, as they seek to establish territory even when housed alone. They may set up a territory centered on a plant or rocky alcove, sometimes becoming highly possessive of it and aggressive toward trespassing rivals; consequently, bettas, if housed with other fish, require at least 45 litres (about 10 gallons). Contrary to popular belief, bettas are compatible with many other species of aquarium fish. Given the proper parameters, bettas will only be aggressive towards smaller and slower fish than themselves, such as
guppies. Betta aggression has historically made them objects of gambling; two male fish are pitted against each other to fight, with bets placed on which one will win. Combat is characterised by fin nipping, flared gills, extended fins, and intensified colour. The fight continues until one participant is submissive or tries to retreat; one or both fish may die depending on the seriousness of their injuries, though bettas rarely intend to fight to the death. To avoid fights over territory, male Siamese fighting fish are best isolated from one another. Males will occasionally respond aggressively even to their own reflections. Though this is obviously safer than exposing the fish to another male, prolonged sight of their reflection may lead to stress in some individuals. Not all Siamese fighting fish respond negatively to other males, especially if the tank is large enough for each fish to create their own designated territory.
Aggression in females In general, studies have shown that females exhibit similar aggressive behaviours to males, albeit less frequently and intensely. An
observational study examined a group of female Siamese fighting fish over a period of two weeks, during which time they were recorded attacking, flaring, and biting food. This indicated that when females are housed in small groups, they form a stable dominance order, or "
pecking order". For example, the fish ranked at the top showed higher levels of mutual displays, in comparison to the fish who were of lower ranks. The researchers also found that the duration of the displays differed depending on whether an attack occurred. The results of this research suggest that female Siamese fighting fish warrant as much scientific study as males, as they seem to have variations in their behaviours as well.
Courtship behaviour 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.
Metabolic costs of aggression Studies have found that Siamese fighting fish often begin with behaviours that require high cost, and gradually decrease their behaviours as the encounter proceeds. In regards to oxygen consumption, one study found that when two male bettas fought, the metabolic rates of both fish did not differ before or during the fight. However, the fish who won showed higher oxygen consumption during the evening following the fight. This indicates that aggressive behaviour in the form of fighting has long-lasting effects on metabolism.
Behavioural effects of chemical exposure Siamese fighting fish are popular models for studying the neurological and physiological impact of certain chemicals, such as
hormones, since their aggression is the result of
cell signalling and possibly genes. One study investigated the effect of
testosterone on female Siamese fighting fish. Females were given testosterone, which resulted in changes to fin length, body coloration and gonads that resembled typical male fish. Their aggressive behaviour was found to be elevated when interacting with other females, but reduced when interacting with males. The researchers then allowed the females to interact with a control group of unaltered females; when the female fish stopped receiving testosterone, those who were exposed to the normal females still exhibited male-typical behaviours. In contrast, the female fish who were kept isolated did not continue to exhibit the male typical behaviours after testosterone was discontinued. Another study exposed male Siamese fighting fish to
endocrine-disrupting chemicals. The researchers were curious if exposure to these chemicals would affect the ways in which females respond to the exposed males. It was found that when shown videos of the exposed males, the females favoured those who were not exposed to the endocrine-disrupting chemicals, and avoided those males that were exposed. The researchers concluded that exposure to these chemicals can negatively affect the mating success of male Siamese fighting fish. A psychology study used male Siamese fighting fish to investigate the effects of
fluoxetine, an
SSRI used primarily as an
antidepressant in humans. Siamese fighting fish were selected as prime models due to having comparable serotonin transporter pathways, which accounts for their aggression. It was found that when exposed to fluoxetine, male Siamese fighting fish exhibited less aggressive behaviour than is characteristic of their species. Similarly, research has found that bettas are responsive to
serotonin, Another commonly prescribed drug that can affect
Betta splendens' behavior is metformin, which is a drug doctors prescribe to treat people with type II diabetes. Metformin can enter freshwater and wastewater areas because it does not always get fully broken down in humans, and whatever does not get fully metabolized is usually excreted through urine or feces. When metformin makes its way through the sewage systems and into betta habitats, over time it reduces the aggression of the male bettas. The longer the male bettas are exposed to concentrated metformin, the more their aggression diminishes. With decreased energy and aggression, the bettas' fitness can decline.
Sleep behavior Betta fish can exhibit unusual sleep behaviors, often resulting in new betta owners assuming that their betta fish has died. In an aquarium, betta fish sleep anywhere in the tank they feel comfortable, including at the bottom on the substrate, floating at the mid-level, or at the surface. Betta fish will sleep on their side, upside down, with their nose pointing up, or with their tail pointing up. They are also known to curl up or wedge between tight spaces, such as behind a heater. One of the more unusual sleep behaviors that betta fish exhibit is their ability to sleep out of the water, resting on a leaf or any other flat object protruding from the water. This is made possible by the betta's labyrinth organ, which acts like a human lung, pulling oxygen from the air instead of from the water. When betta fish sleep, their bright colors will often fade, and when combined with their unusual napping positions, they can appear dead. Predatory fish will often avoid eating a dead fish because of the risk of contracting diseases and parasites, making this an excellent defensive mechanism. == Genetics ==