Dieting fish avoid fights

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Australian scientists have found that some fish diet to avoid fights.

In a study published in a recent issue of the journal Current Biology, Marian Wong, Philip Munday, Peter Buston and Geoffrey Jones of James Cook University studied the effects of food competition versus conflict over rank on subordinate growth rates in the group-living reef goby Paragobiodon xanthosomus.

The authors write Paragobiodon xanthosomus is a goby that lives in colonies of the coral Seriatophora hystrix. Inside colonies, they form groups of up to 20 gobies: a breeding male and female (dominant breeders) plus several smaller non-breeding females (subordinate non-breeders).

"Subordinate non-breeders are organised into a size-based hierarchy with each female remaining consistently smaller than the one ranked above it.

"Hierarchies function as queues for breeding. When a dominant dies, all subordinates below it grow and shift up in rank. Only when they reach the front of the queue can they breed.

The authors studied colonies collected from the northern Great Barrier Reef, and experimentally manipulated food availability and the presence of the dominant, breeding female in natural social groups maintained in aquaria.

This was done by training subordinate non-breeders (but not dominant breeders) within natural groups to feed from a supplemental food source having removed or not removed the dominant breeding female.

They found that the fourth-ranked individuals in approximately half the groups studied abruptly ceased feeding despite no feeding interference from dominants while the fourth-ranked individuals in the remaining groups that continued eating were evicted from the group by their dominants.

The authors surmise that hese results support the view that subordinates can reduce their food intake, and hence their growth, when conflict over rank intensifies, and that such self-imposed growth restraint is beneficial as subordinates otherwise suffer high costs from being evicted.

They also conclude that since iet restriction has also been shown to prolong lifespan in many species, so diet restriction in P. xanthosomus may also enhance a subordinate s chances of outliving its dominants and inheriting breeding status.

For more information, see the paper: Wong, MLY, PL Munday, PM Buston and GP Jones (2008) Fasting or feasting in a fish social hierarchy. Current Biology 18, pp. R372"R373.