Fighting Fish Shown to Synchronize Their Combat Moves

This is a Siamese fighting fish, Betta splendens. (Photo courtesy of Ivabalk, Pixabay)

(CN) — Famous for its aggression, betta fish may soon be known for a milder trait: cooperation.

When two Betta splendens fight for dominance, not only do their attacks mirror each other, but the gene expression in their brain cells also starts to align, according to a study published Wednesday in PLOS Genetics by Norihiro Okada of Kitasato University in Japan.

The new findings, which show their brains cooperating at the molecular level, helps explain how the fish synchronize their fighting behavior, which appears more closely choreographed the longer the fight lasts.

Commonly used to study aggression in the lab, the small freshwater fish employs a handful of standard tactics like mouth-locking, bites, strikes and swimming to the surface to gulp air.

“Betta males are extremely aggressive and have stereotypical social displays,” according to the study.

In their natural habitats, males fiercely protect their territories, where they build a bubble nest to hold fertilized eggs. In the lab, a male aggressively attacks any intruder or its own mirror image to maintain its territory.

Physiological and neurological studies using bettas in combination with drug treatments have helped scientists identify some important signaling molecules linked to aggression, such as serotonin and dopamine.

But previous studies on bettas and other fish usually described only one particular behavior such as displaying, biting, or striking or compared differences in aggressiveness between the loser and the winner. Aggression in animals may increase an individual’s chance to survive and transmit its genes to the next generation.

In the new study, researchers observed that during a fight, two male opponents modify their actions to match the aggressive behavior of the other, leading to coordinated battles.

Researchers videotaped hours of fights between 17 pairs of fish to scrutinize each fight. By analyzing the brains of both opponents, they observed that the fish also synchronized which genes were turned on or off in brain cells. The fighting pair had similar changes in gene activity related to learning, memory, synapse function and ion transport across cell membranes.

The synchronization was specific to a fighting pair and became stronger after fighting for an hour compared to a 20-minute fight, ”suggesting that the degree of synchronization was driven by fighting interactions.”

Okada’s study takes a new approach to the question of how animals synchronize their behavior by focusing on how the genome of an organism influences the development and function of its nervous system. Similar mirrored behaviors also occur during mating, foraging and cooperative hunting, and these behaviors may also trigger synchronized brain changes in the pairs of animals.

“One of my future plans is to elucidate what happens in the male-female interaction of fish on the molecular level,” Okada said.

The findings suggest that even though the betta fish are fighting each other, sometimes to the death, their brains may be cooperating at the molecular level.

“By measuring aggressive behavior displays (bite/strike/surface- breathing) between two opponents during fighting, we demonstrate that the two opponents in each fighting pair showed similar fighting configurations by influencing each other,” Okada and his team wrote in PLOS Genetics.

“In addition, we compared brain gene expression between opponents and showed synchronization of gene expression within a fighting pair, leading to pair-specific synchronization in genes associated with ion transport, synapse function, and learning and memory.”

Behavioral and physiological synchronization have long been studied by scientists, given its importance in mating, cooperative behavior and aggression.

The study presents the possibility that similar behaviors in pairs of animals under similar conditions may trigger “synchronizing waves of transcription” between the individuals, supporting the idea that fighting behaviors contain cooperative molecular aspects, according to Okada.

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