Researcher produces egg-laying male fish

A researcher at Ohio State University says he is working on producing larger bluegill by breeding super males with two Y chromosomes.

The male bluegill are about twice as big as females and thus more profitable for fish farmers, The Columbus Dispatch reported Sunday.

Han-Pin Wang, a researcher in the Ohio State aquaculture lab, uses a method based on the genetic difference between males and females. Like humans, male bluegill normally have an XY chromosome pair while females have XX.

Wang gives the fish estrogen to produce males that are biologically female -- they can produce eggs -- but are genetically male. He uses ordinary males to fertilize the males.

By the law of averages, about one-quarter of the resulting offspring will be female, half male and one-quarter super males. When the super males mate with females, all the offspring will be male.

Wang said his method is environmentally safe because the use of hormones is confined to laboratory tanks.