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SYDNEY: Like humans, little fish also diet - not to look more presentable, but out of dire necessity. They don't want to get on the wrong side of more dominant fish and risk being gobbled up.

A new study, by researchers at James Cook University, has also found that bigger fish use the threat of punishment to keep competitors in line.

It has been noticed that among goby fish only the largest two individuals, a male and female, have mating rights within a group. All other group members are non-breeding females, each being consistently 5-10 per cent smaller than its next largest rival.

The new study sought to find out how they maintain this precise size separation, ScienceAlert reported.

The reason for the size difference was easy to see, explained Marian Wong, who led the study.

“Once a subordinate fish grows to within 5-10 per cent of the size of its larger rival, it provokes a fight which usually ends in the smaller goby being expelled from the group - and the safety of the coral it occupies. More often than not, the evicted fish is then gobbled up by a predator.”

It appeared that the smaller fish were keeping themselves small in order to avoid provoking the big fish. Whether they did so because of stress caused by the bullying of larger fish or voluntarily - by restraining how much they ate - was not clear.

While the habits of gobies may seem a little arcane, Wong explained that understanding the relationships between dominant and subordinate animals is important to understanding how hierarchical societies remain stable.

Source: TOI