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Fight-Watching Fish Can Figure Out Local Pecking Order, Study Shows

Mason Inman
for National Geographic News
January 24, 2007
 
The first rule of fish fight club is, remember who your rivals beat. The second rule of fish fight club is, remember who they lost to.

A new study shows that fish can watch their rivals face off and then figure out where they all rank compared to each other.

The fish were able to sort out the entire local hierarchy from seeing a limited number of fights between select pairs of their neighbors, the study showed.

This is evidence of surprising social savvy among these fish, Astatotilapia burtoni, a type of African cichlid. (Related: "Lost African Lake Spawned Fish Diversity 'Beyond Belief'" [May 4, 2005].)

The new findings will be presented in tomorrow's issue of the journal Nature.

Key to Survival

The fish's ability to gauge rivals' fighting strength is crucial to helping the animals figure out when to fight and when to flee.

The males of the species fight fierce battles over territories in lakes and rivers, since having a good plot is the key to scoring food and winning a mate. (Related video: "Cichlid Fish Mouth Fighting".)

"How many fights they win or lose ends up determining their reproductive success," said Logan Grosenick of Stanford University, who led the study.

"This results in a strong evolutionary pressure on them to use social information" to choose their fights wisely, he added.

A similar ability to learn a hierarchy from limited information has been shown in a few other animals, including monkeys, rats, and pigeons.

But those studies usually involved more artificial situations, where the animals get rewards from researchers for choosing the right answers.

This new study, on the other hand, showed the fish could learn the hierarchy on their own, just by watching.

Ringside Seat

To figure out what was going on, Grosenick and colleagues kept one fish, the observer, in a central tank with windows onto other tanks.

Then they staged a series of rigged fights between other fish.

For example, they stressed a fish and then put it into another's tank, setting it up to lose to the fish that was in its home territory.

The home fish chased and bit the invaders, and the invaders consistently fled, Grosenick said.

And when the fights were on, the observer fish "sat there, attending to the fights, like they're watching television," he added.

After the observer fish watched a bunch of these fights, the researchers tested them on their understanding of the hierarchy.

The researchers let the observer fish choose between two fish that they'd never seen fight before.

The observers preferred to swim near those that were lower in the hierarchy. Presumably, the observers felt safer away from the more dominant males.

Widespread Behavior?

"This [study] shows possible evolutionary origins" of this kind of inference, said Thomas Zentall of the University of Kentucky in Lexington.

"It's saving the fish from getting attacked as much as they might otherwise," Zentall said.

"It must have considerable value," he added. "Even though they have a small brain, they're able to process this kind of information."

This ability may be widespread, study leader Grosenick added.

"I would expect this in most species that have dominance hierarchies."

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