The beta fighting fish or Siamese fighting fish is one of the most popular freshwater aquarium fish.

Both instinctive and learned behaviors of the beta fighting fish or Siamese fighting fish have been studied in much detail.

Its aggressive responses are easily triggered by its own reflection in a mirror. The ability to turn aggressive behavior on and off, without putting the beta fighting fish or Siamese fighting fish at the risk of physical damage, made the fish a popular by psychologists interested in studying aggression.

There was a stream of research on the beta fighting fish or Siamese fighting fish's aggressive behavior in the 1970s.

This has reduced lately, partly because of new approaches to studying aggression arising out of sociobiology, and partly because it was realized that, even if no tissue damage was evident, repeatedly eliciting aggressive responses in the beta fighting fish or Siamese fighting fish might be a significant source of stress.

Interesting results were obtained, however; for example was shown that the presentation of such an aggression-eliciting stimulus will act as an unconditional stimulus in classical conditioning, and as a reinforcer in operant conditioning. It is as if the fish finds the opportunity to attack another fish rewarding.