Betta Splendens Are Right And Left Handed?

What?! The Betta Splendens, better known as betta fish to the tropical fish hobbyist, actually shows left- and right-handed preferences? In raising bettas for twenty years, I do not think I have ever noticed this or given it much thought for that matter, but lead researcher Yuichi Takeuchi of “Behavioural Brain Research” has studies that show exactly that. Takeuchi also explains that the studies show a corresponding body symmetry as well.

This may mean that bettas have a “good side” and “bad side” just as we humans think we do when taking pictures. In these studies, Takeuchi wanted to answer three questions:

  • When flaring, or showing aggression, did betta splendens consistently favor one side or another to present to his opponent?
  • Are there differences in the appearance or physical characteristics in betta fish from left to right side?
  • Are differences in bettas’ body shape directly linked to which side the fish displayed when flaring (showing aggression)?

As it turns out, bettas were the perfect candidate for such a test because they show hyped-out aggressive behavior patterns at predictable times and can easily be made to enter this type of behavior. When male bettas see another male betta, or even other species of fish that resembles a male betta, they extend their fins and tail as high and long as possible, puff out their chest, and will even attack if the fish is in the same tank.

In the first phase of the experiment, Takeuchi noticed that when placed in an eight-sided betta tank with mirrored walls, a little more than half the betta fish showed a left or right-sided inclination for their aggressive behavioral displays of aggressions. “Right-handed” bettas were more likely to flare their right sided gill covers, and left dominant bettas the left side.

In the next stage, the researchers looked for tiny differences in the physical makeup of the fish. They paid special attention to the angle at which the fish’s spine contacted its head. The vast majority of betta splendens had a sever right or left bend to their backbone.

Lastly, Takeuchi then looked at both sets of data in respect to the other. Did the bettas prefer their right or left side because of the bend in their backbone, or did they get the bend because they had favored that side in the first place? Amazingly, the fish that preferred one side or the other had a bend in that direction.

Dr Claire Inness posted this news on Practical Fishkeeping.

Want to know all about betta fish, and total betta care? Check out the Betta Blog at for more great Betta Fish news and articles.

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Published in: on May 21, 2010 at 6:01 am  Leave a Comment  

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