A pair of rabbitfish feed, one eating while the other watches for danger. Photo by James Cook University/Jordan Casey

CAIRNS, Australia, Sept. 28 (UPI) -- New research suggests companionship isn't a behavior exclusive to highly social mammals and birds. Fish, too, are capable of reciprocal cooperation.

In a new study, published this week in the journal Scientific Reports, scientists find that rabbitfish pairs exhibit cooperative feeding behavior.


"We found that rabbitfish pairs coordinate their vigilance activity quite strictly, thereby providing safety for their foraging partner," lead study author Simon Brandl, a researcher at James Cook University's ARC Centre of Excellence for Coral Reef Studies, said in a press release.

"In other words, one partner stays 'on guard' while the other feeds -- these fishes literally watch each others' back," Brandl added. "This behavior is so far unique among fishes and appears to be based on reciprocal cooperation between pair members."

Reciprocal behavior requires a certain level of social intelligence -- the ability to understand that a momentary sacrifice for the benefit of another will be repaid by a companion.

It's been assumed that fish lack this social intelligence. That assumption has now been undermined.

"By showing that fishes, which are commonly considered to be cold, unsocial, and unintelligent, are capable of negotiating reciprocal cooperative systems, we provide evidence that cooperation may not be as exclusive as previously assumed," Brandl said.

Brandl's colleague and study co-author, David Bellwood, says their work should inspire researchers to examine the social behavior of fish more closely.

"Our findings should further ignite efforts to understand fishes as highly developed organisms with complex social behavior," he said.