Betta Splendens are known for their intense aggression, which has resulted from intense selective pressures imposed upon them from many generations of artificial selection. Fighting strains of B. splendens (Plakat) have been bred for aggression for over six centuries due to the culture surrounding fighting betta fish and betting money on the results. This has genetically differentiated them from their wild-type counterparts – fighting strains of Plakats have been shown to be significantly more aggressive than wild bettas, and in addition show differential responses in cortisol production in new environments. It is also known that various bloodlines within the Plakat strain behave differently according to it’s breeders desired characteristics.
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When two betta fish are fighting for dominance, not only do their attacks mirror each other, but the gene expression in their brain cells also starts to align. The new findings, published June 17th in PLOS Genetics by Norihiro Okada of Kitasato University, Japan
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 tightly synchronized battles. Furthermore, when the researchers analyzed 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.
There is also evidence that the genetic basis for aggression in betta fish is not exclusively sex-linked – a recent study found that female bettas of the fighting strain show significantly higher levels of aggression than their female wild-type counterparts, here at FightingBettas we have demonstrated how aggressive our female Plakats can be despite the fact that historically only male bettas have been used in fights and thus artificially selected for aggression.
