The small tropical fish, commonly found in home aquariums, and humans share much of the same genetic material, so what scientists learn about how a zebrafish egg develops into an adult can shed new light on human development, especially its initial stages. But they have limited usefulness in developmental studies. Xenopus has twice as many chromosomes as humans and it takes individuals years to mature and reproduce. Mice breed more rapidly, but they carry their embryos within their bodies, making the initial development stages difficult to study. Zebrafish, by comparison, lay eggs that are transparent and that develop outside the body, making them particularly easy to study.
Development is also rapid, proceeding from fertilization to hatching in only three days.
The fish are also easy and inexpensive to raise, so scientists can keep thousands of them in a laboratory. Sequencing of the zebrafish genome has been initiated in the United Kingdom, substantially increasing the zebrafish s value as a model for the molecular analysis of development. As a result, zebrafish are poised to become the vertebrate version of the fruit fly Drosophila. For nearly a century, geneticists have conducted experiments with fruit flies that have significantly advanced scientific understanding of the molecular basis of heredity but, until now, they haven t been able to do comparable experiments on vertebrates.