(Cleaner Fish On The Job; By Nhobgood) Blue-streak cleaner wrasses live in harems. Dwelling amongst the coral reefs in the Indo-Pacific, the male carefully watches over his group of consorts, making sure that other males keep their distance. But the sole male cleaner fish also faces a threat from within his group: A female can usurp his spot. In fact, any of the females can change their sex – producing sperm instead of eggs within a few days – if they get large enough. To keep his ladies as ladies, the head honcho strictly enforces a diet. Females that are close in size to the head male are punished more severely by him if they get selfish at the dinner table than small females, according to a recent study led by the Institute of Zoology in London and published in the Proceedings of The Royal Society B. The larger the female, the nearer she is to undergoing a sex change, so the male doesn’t like it when she eats too much. And he makes that dislike clear. Cleaner fish eat the...