These fish fight so hard they have to build rest breaks into their battles

Male Siamese fighting fish of southeastern Asia like to assert dominance the old-fashioned way: by beating the fishy crap out of any other males they see. And yet they seemingly have a gentleman's agreement about when to take a breather.

Siamese fighting fish, also known as Betta, originated in the rice paddies of Thailand, Cambodia, Vietnam, and Malaysia. Those waters are relatively low in oxygen, and so the species has adapted with an organ that allows it to breathe the air when it breaks the surface. The trade-off is that its gills have become smaller, which means that the fish can't stay underwater indefinitely if they're engaged in a high-energy activity. And as Dr. Steven Portugal of London's Royal Veterinary College explains over at BBC News, there's no higher energy activity than males fighting for dominance:

"It seems their smaller gills, a result of living in low oxygenated water, cannot keep up with the vigor of the fight, and more air breathing is required. The males of the species are ornate and very aggressive towards members of the same sex. Historically, the local people of south-east Asia have taken advantage of this aspect of their behavior, and fought them against each in tank arenas, in a similar fashion to cock-fighting."

Dr. Portugal's research has been rather more scientifically rigorous than those fish fights, placing a pair of fish in separate bottles inside the same tank. Although physically separated, the fish could see each other and began putting on aggressive displays immediately, which allowed Dr. Portugal to observe just how these fish balance their need for extra oxygen with the risk of exposing themselves to attack. The solution, it turns out, is for both fish to essentially agree to come up for air at the same time. It actually sounds an awful lot like the Siamese fighting fish equivalent of some rudimentary game theory, as Dr. Portugal explains:

"If your foe needs to breathe first, you might be forgiven for thinking this is the best time to strike - he's weak enough to have to breath first, turns his back to surface for air, [it's] seemingly the best time to attack. However, if your attack at this point is not successful, your opponent comes back to carry on fighting you with plenty of oxygen... Eventually, you will have to surface to breath too, and potentially suffer the same fate of being attacked. Therefore, by both surface-breathing at the same time, neither of you are risking being attacked by the other during the ascent and descent from the surface. It seems they can't even take in more oxygen per breath, so these fights are seriously demanding for the fish."

For more, check out BBC News and the original paper over Comparative Biology and Physiology Part A.

Image by Rae134 on Flickr.