The Striped Crusader

The majestic zebrafish. Photo source.

This minnow-sized aquarium fish from India seems like an unlikely hero for the scientific community, but it’s hard to judge a fish by its stripes. The zebrafish became a notable model organism for developmental biology in the early 90s and has remained as one of the important organisms in the field ever since. But what makes it so great?

Until the advent of the zebrafish as a model, developmental research was done largely in the fruit fly, and the mouse. The fruit fly has a relatively small genome, and is exceptionally easy to raise (keeping them off your lunch is the hard part), so it is easier to find important developmental genes.  The main limitation to the fruit fly is that it’s only distantly related to us; it’s an invertebrate (doesn’t have a backbone). The mouse is a mammal, like us, so its genes are very similar to our own. The main limitation to  is that the embryo develops inside the mother, making it impossible to see development as it happens.

Fruit fly (source) and mouse (source).

Fruit fly (source) and mouse (source).

Zebrafish, therefore, offer an optimal middle ground. As vertebrates, zebrafish have many of the same genes that we mammals do, allowing researchers to expand some conclusions from work they do with the zebrafish onto how the system might work in humans. They also lay eggs, so the embryo develops outside the adult and can be observed through its entire development.

Another benefit to using zebrafish as a model organism (an animal that is widely studied) is they lay translucent eggs, which are externally fertilized. This is great because it allows scientists to watch development all the way from a single cell to the adult. Their development also happens relatively quickly. The time from a single cell to a newly hatched fish (called a larva) is around two days! There’s a lab in Belgium that has taken some great photos of larva, like this one. You can see the larvae within the egg almost ready to burst out.

Zebrafish embryos and larva. Photo source.

Larval fish change dramatically as they develop after hatching, taking on the shape and pigmentation of the adult fish. This allows researchers to investigate later stages of development (called postembryonic development). Most research in the field of developmental biology has been on describing how an organism gets from a single cell to an embryo (no small task!). This encompasses how an embryo can tell its head from its feet, its insides from its outsides, and its back from its front; how organs develop; and how cells know where to migrate to make their designated tissue. It’s a lot to cover! But, a lot of growth and change happens to all animals between infancy and adulthood. Zebrafish provide an excellent organism in which to study this change, making it a great organism to make even larger strides in the field of developmental biology.

Further Reading

Meredith Bache-Wiig received a BA in Biochemistry and Molecular Biology from Gustavus Adolphus College in 2013. She is now in the Biology PhD program at the University of Washington Seattle investigating the role of thyroid hormone signaling in postembryonic pigment pattern formation in zebrafish. When not in lab, she enjoys reading, cooking, training for triathlons, and occasionally swing dancing.