Siamese Fighting Fish

The Siamese fighting fish (Betta splendens), also known as the Betta, is a species in the Gourami family. They are called pla-kad (biting fish) in Thai. They are a highly aggressive fish that typically are unable to be kept in community tanks - even the females may kill each other. The species are native to the Mekong basin of Laos, Cambodia, Vietnam and Thailand. In January 2014 a large population of the fish was discovered in the Adelaide River Floodplain in the Northern Territory, Australia. As an invasive species they pose a threat to native wildlife

Bettas are sometimes compatible with other species of aquarium fish but are known to be more aggressive towards smaller fishes that resemble them, than larger ones that they can clearly distinguish as other species. In general, they're also less aggressive towards fishes that are less colourful. The aggression of the fish has been studied by ethologists. The fish have historically been the objects of gambling; two male fish are pitted against each other in a fight and bets are placed on which one will win. One fish is almost always killed as a result.