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The Why and How of Breeding Zebrafish for Research

Zebrafish take no time at all to develop--one of their many advantages as a model organism.
Zebrafish take no time at all to develop--one of their many advantages as a model organism.

Why zebrafish?

Zebrafish (Danio rerio) are used pretty frequently in scientific research for several big reasons.

1. They're an awesome model of human development

It can be hard to believe that zebrafish and humans have anything in common, but our developmental processes and genomes are actually very similar. So much so in fact that zebrafish are currently used in a myriad of studies of human health looking at "human genetic disease, caveolin-associated muscle disease, homeostasis, kidney development and disease, cancer, cardiovascular disorders, oxidative stress, caloric restriction, insulin-like pathways, angiogenesis, neurological diseases, liver disease, hemophilia, bacterial pathogenesis, apoptosis, osteoporosis, immunological studies, germ cell study, Bardet-Beidl syndrome gene (BBS11), Alzheimer's disease, virology studies and vaccine development," according to the 2007 journal article "The Zebrafish Model: Use in Studying Cellular Mechanisms for a Spectrum of Clinical Disease Entities."

That's quite the list! From my own experience, zebrafish also make excellent models for toxicological studies; environmental factors like pesticides that negatively effect zebrafish (specifically looking at neuronal and cardiac development) more than likely have a similar affect on humans.

Transparent embryos means you can see the whole organism develop easily.
Transparent embryos means you can see the whole organism develop easily.

2. Their embryos are transparent

Because zebrafish embryos are transparent, they are ideal for real time in vivo studies. This is a gold star in research because your laboratory results far more closely mirror what happens naturally, or in a less controlled environment (like "out in the world"), than in in vitro studies. A transparent embryo means they are easily visualized without being tampered with.

A male zebrafish (upper) and a female zebrafish (lower).
A male zebrafish (upper) and a female zebrafish (lower).

Here are two zebrafish in a spawning tank (the size I use)

3. They reproduce like mad

As with most fish, zebrafish can lay dozens of eggs in one cycle, making it easy to work with large sample sizes and thus ensuring more trustworthy results.

To breed zebrafish, the method that I employed yielded about 20 embryos per tank, and fish were only set up for breeding for less than 24 hours, meaning no accommodations had to be made for feeding or cleaning, which is convenient for smaller labs that may not have a huge starting colony or supplies to work with.

  1. Zebrafish should be kept at 28°C in a 14-hour light/10-hour dark cycle.
  2. As opposed to the marble method, which requires additional cleaning and careful siphoning of the embryos for collection, spawning tanks are a helpful alternative. As described in the 2012 article "An inexpensive, efficient method for regular egg collection from zebrafish in a recirculating system," a spawning tanks "consist of a bottom reservoir, a lid, and an insert that fits in closely into the bottom reservoir. When the fish breed, the eggs fall through holes of the insert and into the reservoir, thus preventing them from being cannibalized. Because fish in these spawning tanks are not fed and do not get fresh water, they are bred only once a week."
  3. After 3 PM the day before you need your embryos (I recommend before 5 PM), in each spawning tank, place male and female zebrafish in at a 1:2 ratio (how many you place will depend on the size of your spawning tank), with more females than males. Male zebrafish tend to be thinner, sleeker, with a more yellow colored underbelly. Female zebrafish tend to be somewhat plumper with a much whiter underbelly.
  4. The fish should be left undisturbed until the next morning. Before noon the fish will have finished their breeding cycle for that day, so eggs should be visible at the bottom of the tank (along with some other unsavory debris). The adult fish can be placed back in their original tanks and the embryos can be transferred to a petri dish or finger bowl using a pipette.
  5. Once the embryos are collected, you can proceed with whatever protocol your experimentation requires.

4. They're inexpensive

Cost is one of the biggest limitations in research. Luckily, zebrafish are one of the least expensive critters to buy from a supplier. The best part is, if you follow the steps above or use a different method, you may only ever need to buy an original dozen or so before you can start your own colony!

Some pet stores may carry the Danio rerio zebrafish, but not all. Your best bet is ordering from universities that breed the fish or from commercial suppliers. Here are some useful links for ordering and caring for adult fish and embryos:

Ordering and pricing from the Marine Resources Center

Zebrafish facility developing and care

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