COMPARATIVE EMBRYOLOGICAL STUDY OF
ZEBRAFISH AND SEA URCHIN EGGS
Biology is the study of life. In this comparative analysis of sea urchin and zebrafish development, students examine the very essence of life itself through study of the developmental stages of the two animals. Due to their different phylogenetic origin, each animal possesses developmental characteristics unique to that species. Both animals have been studied extensively in embryological research and are easy to obtain and culture. The simplicity of these activities as well as the ease and dependability with which they can be performed makes these labs ideal choices for classroom study. Although numerous high school and university teachers nationwide currently use the sea urchin development lab, I recommend that both animals be used to provide students with a much more thorough embryological investigation than can be attained using either species in isolation.
differentiation holoblastic cleavage
blastula meroblastic cleavage
The combination of the two labs requires approximately three 80 minute class periods to complete. Additional time in subsequent periods can be used for discussion and review. These labs are best utilized after completion of a basic Mendelian genetics unit or in a Biology II class.
Many high quality sea urchin and zebrafish embryology labs already exist in various lab manuals. This activity is not designed to duplicate those efforts but rather to complement and enhance them. The purpose of this activity is twofold. First, rather than developing or redesigning an activity to add to an already impressive collection of urchin and zebrafish labs, the intent of this activity is to provide teachers with the information they need to obtain and perform one of the numerous preexisting developmental labs on urchins and zebrafish. After completion of a lab on each animal, the second purpose of this activity is to then have students examine the similarities and differences in development between a representative invertebrate and vertebrate animal.
The sea urchin development lab has been the classic method of embryological study used for many years by numerous high school and university teachers nationwide. Urchins have many positive attributes for study in the school setting. They can be collected at no cost by teachers living close to the ocean or purchased from a biological supply house by teachers who do not have access to saltwater. Once collected, they can easily be induced to spawn and will shed millions of gametes. Students view the sperm and eggs separately and then mix the gametes and observe the moment of fertilization and formation of the fertilization membrane to prevent polyspermy.
Development of the fertilized urchin egg is rapid and dramatic with the first division occurring within two hours of fertilization. The embryonic blastula hatches in just over 24 hours and the pluteus larvae can be observed within 72 hours of fertilization.
The zebrafish development lab is an ideal complement to the urchin lab for several reasons. Zebrafish, Danio rerio, also develop very rapidly, moving from a single cell to a multicellular, free-swimming fish in only three days. In addition, as a vertebrate animal, they display many characteristics not present in sea urchins. They have a transparent yolk through which students can clearly observe a pulsating heart only 24 hours after fertilization, formation of well developed eyes, development of a neural and skeletal system, and blood circulation. Their yolk is so clear that one well-known researcher compared watching the actively dividing cells to "growing cells in a living petri dish." Furthermore, these fish can be purchased for a very low price at almost any tropical fish store. Commonly called zebra danio by tropical fish enthusiasts, they are small, hardy, and easy to care for.
The sea urchin and zebrafish both have advantages and disadvantages when used in developmental labs. However, when used in conjunction with each other, they provide a thorough examination of embryonic development and enhance both student interest and learning.
Materials for the Sea Urchin Lab
Numerous good sea urchin development labs are available in various lab manuals. An excellent embryology lab is in The Biolab Book by Lundy Pentz, 1989, Johns Hopkins University Press. Another good urchin lab and excellent collection of student research projects using urchins is in
A Lab Manual - Sea Urchin Activities by Ron Anderson and Dan McDonnell. Copies of the manual and other classroom activities can be obtained free of charge by contacting Dr. Steven B. Oppenheimer, Department of Biology, California State University, Northridge, CA 91330.
Materials for the sea urchin lab are available from many sources. The best source for individual teachers usually depends on where they live. A significant amount of money can be saved if teachers collect their own urchins. The author lives on the coast and collects live adult green sea urchins, Strongylocentrotus droebachiensis, for free right off of the dock pilings. Most states require an educational collecting permit from their State Department of Fish and Game to collect. If you live near saltwater, contact your local Fish and Game for collecting regulations in your area.
If live urchins can be collected by the teacher, the only costs for the lab are for a small amount of potassium chloride and for the hypodermic needle to inject it. Green sea urchins need cold water for their larvae to develop. After uniting the sperm and eggs, students add a small amount of saltwater and stack their petri dishes in a refrigerator for development. They monitor development for the next two days during class, at lunch and after school.
If a saltwater aquarium is not available, the larvae can be released back into the environment once they reach the pluteus larvae stage. After the second day, the larvae can be transferred to a refrigerated saltwater aquarium for further development. If the adult urchins are from a warm water environment, it is not necessary to refrigerate their eggs during development. The eggs will develop very well inside a petri dish at room temperature.
Teachers who cannot collect their own urchins can purchase sea urchin kits containing all of the materials and instructions from many biological supply houses. Prices vary considerably and in some areas of the country the urchins are not ripe and available throughout the year. Listed below are several supply houses that can be contacted for further information.
- Gulf Marine Labs, Inc. P.O. Box 237, Panacea, FL. 32346 (904) 984-5297
- Pacific Biomarine, 124 N. Ash, Inglewood, CA. 90301 (213) 677-1056.
- Marinus, Inc. 1400 W. 7th Street, Long Beach, CA. 90813 (213) 435-6522
- Carolina Biological Supply, 2700 York Road, Burlington, N.C. 27215 1-800-334-5551
- Wards Natural Science, Inc. P.O. Box 92912, Rochester, N.Y. 14692 1-800-962-2600
Materials for the Zebrafish Lab
Numerous labs and information concerning the zebrafish are available, many of which can be obtained free of charge off of the Internet. The following might be considered:
- The Zebrafish Book - A Guide for the Laboratory Use of Zebrafish, Monte Westerfield, University of Oregon Press, 1993, http://zfish.uoregon.edu/zf_info/zfbook/zfbk.html
- Zebra, Zebra, Where Are Your Stripes? Observing Embryological Development in the Zebrafish, Barbara McGlone, Woodrow Wilson Neurobiology Institute Module, 1996.
- Developmental Dynamics, Vol. 203 Number 3, Wiley-Liss, 1995.
The equipment for culturing zebrafish is inexpensive and available in most tropical fish stores and biological supply houses. The aquarium tank, pump, and filter can also be purchased at a much reduced rate at moving sales. As with any tropical fish, set up the tank and let the water culture for two to five days before adding the live fish. Equipment required to maintain the fish includes:
- 1 ten to twenty gallon aquarium with filter, pump, and light
- 1 five to ten gallon aquarium without filter or bubbler for the newly hatched fish fry
- glass marbles for the eggs to settle down into for protection from the adults
- 1 small siphon hose to collect the eggs from down in the marbles
- 1 box to place over the tank to control the amount of light entering the tank
- 1 small inexpensive timer to turn the light on and off
- 1 aquarium dip net
- flake fish food
These embryology labs can logically lead into a unit on DNA and DNA biotechnology. Excess sperm from the sea urchin fertilization lab can be collected and frozen for later use in a lab on DNA extraction. Many labs on DNA extraction exist and can easily be modified to use urchin sperm as the source of the DNA. For an example of a good DNA extraction lab, consult Judy Brown's Onion DNA extraction lab published in the NABT Sourcebook of Biotechnology Activities.
In addition to the previously cited curriculum materials, many sources of information on sea urchins and zebrafish development are available. You might consider the following:
1. Oppenheimer, Steven B. Embryological Research, The Science Teacher, vol. 56, pp 40-43, Nov. 1989.
2. Oppenheimer, Steven B. and Lefevre, George Jr. Introduction to Embryology. Allyn and Bacon, 1989.
3. Oppenheimer, Steven B. The Sea Urchin Embryo: A Remarkable Classroom Tool. The American Biology Teacher, vol. 51, no. 6, Sept. 1989.
4. Pines, Maya. (editor), From Egg to Adult - A Report From the Howard Hughes Medical Institute. Bethesda, MD. 1992.
About the Author
Stan Eller is a biology and advanced science teacher at Homer High School in Homer, Alaska. He can be contacted at Homer High School, 600 East Fairview, Homer, AK 99603 or by e-mail at email@example.com
NAME DATE PERIOD ________
STUDENT ACTIVITY SHEET
1. What similarities do you see between the cleavage pattern of sea urchins and zebrafish?
2. What differences do you see between the cleavage pattern of sea urchins and zebrafish?
3. Compare and contrast gastrulation between the zebrafish and the sea urchin.
4. What stages of embryology in sea urchins are most useful for teaching purposes? Explain.
5. What stages of embryology in zebrafish are most useful for teaching purposes? Explain.
NAME DATE PERIOD ________
STUDENT ACTIVITY SHEET
(This graph was made using ClarisWorks and saved as "Urchin vs Zfish Graph 2". It would not paste here. See hard copy of module for an example of the graph.)