Meet the Casper Fish

by Carolina Staff

Many researchers use zebra fish (Danios) for genetic and developmental studies. Zebra fish make excellent model research organisms since they are vertebrates, and their embryonic development is similar to human embryonic development. This means that you can easily view their internal organs, including the heart, gallbladder, circulatory system, brain, spine, eggs in females, and the swim bladder in males.

Engineering a Solution to a Problem

Researchers at Children’s Hospital Boston had been using zebra fish to study the development of cancer in vivo. However, the window for them to track the cancer was limited to the embryonic stage of zebra fish, where they could see into the bodies of the developing fish. In response, researchers began crossbreeding specific genetic strains of zebra fish to produce a transparent fish. After a year, they developed the Casper Fish, which lacks pigment in its skin and scales, and therefore is transparent. The Casper Fish’s transparency allowed researchers to extend their research into the adult stage of this model organism.

It’s All in the Genes

Two genes were involved in the development of the Casper Fish. The mitfa gene controls development of the melanophores, which are the black pigmented stripes on zebra fish. The nacre allele (n) corresponds to a mutation in the mitfa gene that is present in the Casper Fish, eliminating the appearance of melanophores. An unnamed gene controls the development of reflective iridophores on zebra fish, and the roy allele (r) corresponds to the mutation exhibited in Casper Fish for this gene. To produce a Casper Fish, both genes must be homozygous recessive mutants (nnrr). Therefore, 2 nacre and 2 roy alleles must be present. Crossbreeding and understanding genetic inheritance allowed for this scientific breakthrough.

Zebra Fish and Casper Fish Studies in the Classroom

The benefits Casper Fish and zebra fish bring to the research laboratory also make them ideal specimens for the science classroom. Classroom studies using these fish facilitate the mastery of the NGSS Core Ideas LS1: Molecules to Organisms and LS3: Heredity: Inheritance and Variation of Traits.

Casper Fish give students the opportunity to observe the internal anatomy of a live organism in real time. With a stereomicroscope, students can observe physiological parameters such as heart rate, respiration, and blood flow. Casper Fish activities can be designed to generate student questions, carry out investigations, propose explanations, collect and analyze data, and make an argument from evidence, all of which are NGSS practices. Numerous Crosscutting Concepts are easily addressed in activities including patterns, cause and effect, and structure and function.

Comparing Casper Fish to wild type zebra fish can lead to robust discussions of adaptation and mutation. While Casper Fish are the result of selective breeding of naturally occurring mutants, GloFish® fluorescent zebra fish are the result of genetic engineering. Keeping the fish together in an aquarium might result in some interesting offspring. Breeding will be more successful with a breeding tank.

Incorporate the Genetics

Carolina is the exclusive distributor of Casper Fish. To bring the excitement of this model organism into your classroom, try the Genetics of the Casper Fish Kit. In this kit, students crossbreed zebra fish males and Casper Fish females and observe the embryological development of the F1 generation. This engaging kit not only allows students to watch cellular division and differentiation, but also incorporates the basics of inheritance. While observing embryological development of the collected transparent embryos, your students construct dihybrid crosses to predict the genotypic and phenotypic frequencies of the F1 and F2 generations. Here is an example of the type of question students think through as they observe these growing embryos daily:

Using a Punnett square, calculate the genotypic frequencies of the resulting F1 generation, assuming the parental generation is true breeding (homozygous for both traits). What fraction of the resulting F1 generation would be Casper Fish?

Maintaining zebra fish in your classroom

Zebra fish are social fish, and they do best when they kept in a school of five or more, depending on the size of the tank. A minimum tank size of 10 gallons (see our recommended aquarium kit) is recommended to give them room to swim, and can accommodate 5 to 10 zebra fish.

Learn more about Casper Fish and the other freshwater fish we offer.

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