Betta splendens are known colloquially as Siamese fighting fish, and for good reason. Bettas are very territorial and aggressive. Although females are not quite as violent as males, a betta of any sex may fight any other betta without hesitation. Even the sight of its own reflection can cause a betta to flare up with aggression. Fights aren't usually to the death as is commonly believed, but they do lead to serious injury.
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