Male fish 'shun greedy females'

A new study has found that cleaner male fish are aware of their female partner's size and they often punishing those who overeat, the 'Proceedings of the Royal Society B' journal reported in its latest edition.

The researchers from the University of Queensland, the Zoological Society of London and University of Neuchatel have now shown that male fish lose more than just a meal from their partner's big appetite -- they also risk the female becoming so large that she will turn into a rival male.

Dr Lexa Grutter, the study's co-author, said that the groups' research shows that male cleaner fish are aware of their female partner's size. "One reason males punish cheating females may be to stop her from eating too much and then challenging his position as the dominant male on the reef."

Cleaner fish feed in male-female pairs by removing parasites from larger "client" fish. While providing this cleaning service, cleaners may get greedy and bite clients rather than sticking to parasites.

This cheating by cleaners causes mealtimes to come to an abrupt end as the disgruntled client fish swims off. Females that bite clients receive aggressive punishment from their male partners for such greedy behaviour. Cleaner fish live in groups led by one dominant male with a harem of up to 16 females. All cleaner fish are born female and turn into males when they become the biggest fish in their group. A male cleaner fish usually partners with the biggest female fish in the harem for cleaning duties.

The research also shows that the male cleaner fish can distinguish between high and low value meals and will punish the female severely if she drives off a high-value client.
Dr Grutter said that the female fish will respond to this punishment by providing better service to high value clients in the future. "This is the first non-human example of where punishment fits the crime and results in the offender adjusting their behaviour according to potential penalties."

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