Coral Reef Fish Starve Themselves to Maintain Social Order

Scott Norris
for National Geographic News
June 28, 2007

Some coral reef fish starve themselves to avoid getting into fights with their larger, dominant neighbors, researchers have found.

Emerald coral gobies live in small groups in which social rank is strictly determined by body size. Within each group only the largest, dominant female mates with the one resident male.

Rather than competing for the top spot, subordinate female gobies often limit their own growth to remain non-threatening to higher-ranking fish.

Underlying this strategy of peaceful coexistence is fear of being kicked out and left to die, the researchers say.

Each goby group of up to 17 individuals occupies a single coral colony that provides food and shelter. (Related: "Young Fish Return to 'Home Reefs' to Settle Down" [May 4, 2007].)

When a subordinate goby approaches the size of a dominant, it risks being forcibly evicted from the social group. Predators quickly snatch up most females driven out of the colonies.

"We believe that eviction results in near certain death," said Marian Wong of James Cook University in Townsville, Australia.

Wong's team found that with such extreme penalties, low-ranking gobies voluntarily go on crash diets to maintain their own modest position in the social hierarchy.

"When [females] reach a size difference of approximately 5 percent relative to their immediate dominant, they suddenly cease feeding," Wong said.

By regulating their size, Wong said, the fish minimize the risk of conflict and eviction.

"Evictions are uncommon in the wild," Wong said. "It is more the threat of being punished that promotes stability, as opposed to the act of punishment itself."

The research appeared earlier this year in the journal Proceedings of the Royal Society B.

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