Rupert Collins offers some insight as to why male Siamese fighters are such aggressive creatures.
Siamese fighting fish (Betta splendens) get their name from their native country (Siam is Thailand), and from the fearsome reputation males have in attacking other males.
Betta splendens is a bubblenesting anabantoid, and the males stake out a territory in which they construct their nest, which in the wild, comprises approximately 1.7 fish per square metre, often as part of a larger breeding aggregation.
Females select their mates on the quality of the territory and nest, so males that can have their pick of the best sites are a better prospect.
Intensity of hostile behaviour is an effective signal as to the quality of the male as a mate, with females in captivity preferring males who win a fight, although this hasn't been demonstrated in wild fish.
When other males are present during courting, a male will increase this courtship behaviour and nest monitoring, maybe to compete for the female's attention.
In the presence of other females, however, male B. splendens alter threat displays to other males, by biting less frequently, remaining further away, and increasing their tail beating and opercular displays. No differences have been observed when another male is present though.
Females clearly use these different signals to assess quality of mate, and small females have been observed to prefer males that are larger. However, males that are too large can inflict serious damage onto a female when they mate, so the female must trade-off the relative benefits of a large, strong male with a big nest, with the harassment she will receive from a pugnacious mate. This may be why males tone down their combative nature when females are watching.
When Fighting fish are watching other males fighting, individuals are able to gather and use this information in subsequent interactions.
Fight club
Fighting competitions with these fish is a century old tradition, which began in largely rural areas of Thailand.
Antagonist Betta are placed in front of one another in glass jars before a fight, and "primed" pre-fight, so gamblers can make stakes based on the apparent aggression displayed, in much the same way as a boxing weigh-in!
In laboratory experiments, it has been shown that the duration of opercular display prior to fighting can effectively predict the size of the bubblenest, and also the result of the final match.
Once a bout is agreed by the fish's owners, the adversaries are placed together in a tall vase-like jar, where they display, intensify in colour, erect their opercula (gill covers), and often immediately begin to bite one another and engage in jaw-locking. An average fight lasts around 2-3 hours, although sometimes competitions are time limited, to prevent exhaustion.
Bouts end when one fish gives up and submits, but they are rarely killed in the ring, with most making a complete recovery under the care of their owners.
The fighting life of a Betta starts at an age of around around four months old and fish are considered to be in their prime at around eight to ten months old. Fighters are usually retired at around twelve months of age. When breeding winning fighters, traits such as size, fighting style, sharpness of bite and stamina are all considered when selecting breeding stock.
Some owners recuperate and "toughen" up their fighters using the astringent, antibacterial properties of Indian almond leaves (Ketapang).
Fish are sometimes reared from fry in isolation by breeders, and this has also been shown in studies to lead to an irreversible increase in aggression.
If fish are isolated just as an adult, however, they are subsequently less aggressive in the short term but more bellicose after priming.
It is difficult to say if these fish "enjoy" this fighting, but in numerous studies, male B. splendens actively chose antagonism with other males, but conversely when given an alternative choice of food, they tended to prefer a meal over a fight!
In addition to B. splendens, other Betta are also used for fighting in Thailand, and these include B. smaragdina, B. imbellis and B. sp. “Mahachai”. Scientists have measured comparative aggression between these species and breeding forms, as well as with wild type forms.
Unsurprisingly, the selectively bred short-fin Plakat fighter was more aggressive than the wild type. There was no difference between wild B. splendens and B. smaragdina in tests, but for some reason, wild B. sp. "Mahachai” were significantly more belligerent than the wild type B. splendens.
Additionally, it has been reported that in order to maximise production of more saleable males, commercial breeders apply androgen hormones to female B. splendens during early development, causing them to change into males. These "males" are then poor reproducers, with a proportion of these domesticated varieties not even showing aggression to conspecific males.