Aggression in Male Betta Fish

Betta fish are known for their colorful displays and aggression towards other members of their species. This is especially true of the males. These fish zealously protect their territory and nests. Because of this males must be separated from one another at all times. Even seeing other males through glass can stress the fish out and cause it to injure itself against the tank wall.

Females can be successfully kept in social groups, however, provided that the fish have enough space to roam in the tank. A single fish will generally establish itself as the leader of the social group and dominate the others, but females do not usually fight among themselves.

The aggressive behavior of Betta fish is what has led them to be traditionally used in a sport somewhat like cockfighting. Because of this, they are called Siamese fighting fish, as well. In some Asian countries, these fish are specially bred for fierceness. Fish used for fighting usually have short fins, unlike the decorative specimens we are used to seeing.

Male Bettas flare their brightly colored fins and gill covers when they feel that their territory is being endangered. As they mature, these fish generally increase in aggression, rather than diminishing. They will attack other male Bettas, as well as fingers and other objects that they mistake for them. The length and weight of their extravagant fins and tails will also increase with age.

When males encounter one another, they will first display to make themselves look as large as possible. If this attempt to fool the interloper does not work, the fish will then swim side by side, head to tail, and beat currents of water against one another. Sometimes they will slap and strike one another with their tails and sides. These actions do not cause injury normally. This behavior can escalate further, with the fish biting at one another's tails and locking their mouths together.

They may stop the battle to surface for air, then return to fighting. A Betta which has capitulated the struggle will clamp his fins very close to his body and assume a head up position. This submissive posture shows the other male that he has surrendered. Males and females sometimes fight also, if the male is placed with the female before she is ready to spawn.

Male bettas often build elaborate nests of bubbles. This is because they care for the young produced by the females. They will produce bubble nests even when there are no female betta fish or fry present, however. The sight of another Betta or changes in water temperature can often stimulate this behavior. Bubble nests are located at the top of the water, frequently under shelter. The male carries the eggs to the nest carefully in his mouth and takes care of the young as they grow.

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