Upon further analysis, the researchers found that it is not only the behavior of bettas that begins to sync up during a battle, but also the gene expression in their brain cells.

Betta fish use aggressive tactics such as bites, strikes, and mouth-locking when facing an opponent. Bettas usually stop fighting after they have had the chance to assess each other’s skills, which helps them avoid getting seriously injured.

In the new study, researchers observed that two male opponents were modifying their actions to match the aggressive behavior of the other.

When the researchers analyzed the bettas’ brain activity, they discovered that fighting fish were activating or deactivating the same genes in their brain cells.

The fighting pair showed similar changes in the expression of genes related to ion transport, synaptic function, learning, and memory, and the coordinated brain activity was unique to each pair.