Ker Than in LiveScience.com:
Scientists have long known that some fish are able to switch their sex, either spontaneously or when exposed to steroids. This led them to suspect that a subset of the population of cells in male fish that normally become sperm, called spermatogonia, might be stem cells that have the potential to become either sperm or eggs.
To test their hypothesis, the researchers isolated spermatogonia from the testes of adult rainbow trout and transplanted them into newly hatched trout of both sexes. In male hatchlings, the transplanted cells developed into sperm, while in females they developed into eggs.
The scientists are currently looking into whether eggs could be transformed into sperm. Other researchers have successfully produced sperm from mice stem cells.
The technique could be used to rapidly breed inbred strains of domestic or research animals with desired genetic traits, the researchers write.
More here.