Life through the lens
Classroom Explorations: Zebrafish Development
> Link to Student Pages
Materials & Equipment
For Observation of development For Sequencing of development
Group Size
  • whole class, individuals & small groups
Preparation
For Sequencing of development
  • Go to zebrafish development stills. The nine images of an embryo are in the order, from left to right, of its developmental stages.
  • Print one set of images per group of students. You can laminate them inexpensively by covering the front and back of the images with wide, clear, packing tape.
  • Cut the images into individual cards. Shuffle the images.
Alternative Approaches
For Observation of development
  • If students cannot access the Web pages themselves, you can project the videos.
For Sequencing of development
  • This part of the activity could be done as a separate exploration or used as an assessment.
Objectives
  • To observe zebrafish embryonic development.
  • To sequence images of a zebrafish embryo into the correct developmental order.
Getting Started
  • Lead a class discussion about zebrafish. Have any students seen zebrafish before? Where? What do they look like?
  • Show the swimming adult zebrafish video and have students read the text above and below the video.
  • Discuss how zebrafish are used as model organisms to study development of the human body.
Observation of development
Procedure
  • Have the class use the link on the student pages to watch the zebrafish development video (or project it for them).
  • Have the students discuss, in general, changes that they observed in the embryo from the beginning to the end of the video.
  • Let students view the series of still images from the movie and record their observations in the table in the student pages.
Sequencing of development
Procedure
  • Provide each group of students with a set of shuffled image cards, and have them put the cards in order and answer the questions on the student pages.
What’s Going On?
Zebrafish develop from a fertilized egg to the hatching stage in about 48 hours under laboratory conditions. Initially, the embryo consists of one cell that looks like half of a clear bubble, which is attached to a large amount of yolk—the food for the developing embryo. The chorion , or eggshell, surrounds and protects the embryo. The single cell divides repeatedly by mitosis . With each successive division, the cells become smaller.

Identifiable structures
After many rounds of mitosis, the cells continue to divide, but they also migrate over the yolk and begin to organize into identifiable structures. You can see a head with eyes, a body, and a tail with visible segments called somites that will develop into various structures including the backbone and muscles. The embryo continues to grow and differentiate, adding pigmentation spots and filling the entire chorion. Prior to hatching, the embryo must develop all of the organs and other structures that it will need to live on its own. At this point most of the yolk has been consumed, although a small amount remains and will quickly be absorbed by the hatchling to provide energy for swimming.

On its own
By the time that the zebrafish hatches from the protection of the chorion, it has a developed a complete digestive tract, nervous system (including the senses), and circulatory system, as well as the muscles and fins it needs to swim, find food, and avoid predators.
Related Activities
> Model Organisms
> Broken Hearts
Acknowledgement
Many thanks to Steve Carpenter, biology teacher in the Santa Rosa, California, school district, for developing a prototype of this activity.