1 hour. The fertilized egg has already divided twice, making four cells.
2 hours. As the cells continue to divide, they get smaller and smaller (there are now 128 of them).
5 hours. The curved line shows where the body will soon take shape.
14 hours. The backbone and eyes are beginning to form.
17 hours. The brain begins to form. The body continues to grow longer.
24 hours. Muscles are taking shape and beginning to twitch.
48 hours. The zebrafish is ready to hatch.

Look Inside a Developing Fish

Use a microscope to investigate developing eggs from zebrafish.

Here you can see inside living zebrafish embryos in various stages of development, see their blood circulate, and compare your own pulse to theirs.

Where: Gallery 4: Living Systems

Exhibit Developers: Joyce Ma, Eyal Shahar, and Kristina Yu, 2017

What’s going on?

Zebrafish are widely studied in biology, and for good reason. Not only are they hardy and easy to grow in a lab, their embryos are translucent, so it’s easy to observe how they develop from a single cell into a newly hatched fish.

A fertilized zebrafish egg develops and hatches within 48 hours. It then takes three months for it to reach adulthood.

Going further

Although zebrafish don’t look much like humans, our embryos follow a similar path during early development, so we can study zebrafish to learn about human development.

For example, there are genetic mutations in zebrafish that cause heart defects that are very similar to mutations that cause defects in human hearts. You may encounter some of these mutant zebrafish in this exhibit. They’re easy to spot because their strangely shaped hearts don’t pump blood very well.