Okinawan researchers succeed in sex-change for fish

November 8, 2013 Ryukyu Shimpo

Masaru Nakamura of the Okinawa Chura Umi Foundation and other researchers succeeded in converting an adult female fish to a male, for the first time in the world. They managed this by administering a drug that stops the synthesis of female hormones. The foundation announced this world-first achievement on November 7.

Some types of fish change sex as they grow, but in this experiment with an adult fish that does not naturally change its sex, they succeeded in converting ovaries to spermaries. Fishes that change their sex only have female chromosomes, so all of their offspring are female. For this reason, considering that people eat fish eggs or ovaries, the researchers hope to apply the results of their experiment to fish-farming.

A joint paper written by Nakamura and Yoshitaka Nagahama, a professor at Ehime University, appeared in the British scientific journal, Scientific Reports on October 17.

In the experiment, the researchers gave fish food and drugs including aromatase, which stop the synthesis of female hormones. The ovaries changed into spermaries for killifish in about two months and in about six months for tilapia.

A male fish can fertilize three or four female fish, so there being more males is advantageous for breeding. This experiment will contribute to the farming of fish that people eat the eggs and ovaries of, such as herring and mullet. It indicates the possibility of germ stem cells that produce both eggs and sperm, existing in the ovaries. If the researchers preserve ovaries in a frozen state they will be able to restore high-quality varieties that have become extinct and rare species.

Nakamura said, “If the level of female hormones declines, germ stem cells change into sperm. We are also pleased to find where the germ stem cell that changes into either eggs or sperm exists.”

(English translation by T&CT, Mark Ealey)

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