The zebrafish (Danio rerio) is a tropical freshwater fish belonging to the minnow and carp family. It is native to South Asia, often found swimming in the rivers of northern India, Nepal, Bhutan, and northern Pakistan. The zebrafish has gained popularity over the past decade for their adaptability and mammal-like organs, cell types and brain functions. More and more scientists turn to zebrafish each year to study the underlying mechanisms that cause genetic or infectious disease in humans, including Alzheimer’s disease, congenital heart disease, polycystic kidney disease and even some cancers. Zebrafish models can also help understand Tuberculosis mechanisms as well as the human influenza virus. It is estimated that over 600 labs worldwide carry out zebrafish research in their wet labs today (Heath, 2020).
Its no question that rats and mice are the go-to and most successful models in neuroscience. Rodents have been extremely effective in behavioral studies involving cognition and learning, and have helped determine which mammalian brain regions and neurotransmitter systems are involved in brain functions. While rodents are evolutionarily more similar to humans, the zebrafish model provides new opportunities for the investigation of vertebrate development and other brain mechanisms through aquatic research (Levin & Cerutti, 2009).
Although vertebrates, zebrafish have many organs and cell types similar to that of mammals. Most of the genes found in fish are also found in humans — and most of the genes that cause disease in fish also cause disease in humans. The human immune system, which fights off disease, is a lot like the immune system of fish and so, theoretically, any type of disease that causes changes in humans could also be modeled in zebrafish.
In addition to the above-mentioned benefits that zebrafish provide in research, here are some ways in which zebrafish have advantages over their furry counterparts:
Size and cost. Zebrafish require much less space and are cheaper to maintain than mice.
Rate of reproduction. Zebrafish reproduce at a rapid rate with each female producing up to a hundred eggs each week – these eggs will develop into mature adults in roughly three months. Mice on the other hand, generally produce litters of one to ten pups and on average, can only bear three litters in their lifetime.
Transparent embryos. Zebrafish embryos are transparent and all internal development can be clearly observed from outside of the living embryo. This allows researchers the ability to study vertebrate development from the vert beginning (i.e. at fertilization) and see results of their experiments in as little as three days. Mouse embryos however, are not clear and develop inside the mother, so the observation of live embryo development like that in zebrafish is not possible.
Availability of mutant strains. Well-characterized mutant strains are readily available in zebrafish models. This is not always the case in mouse models.
Life span. Zebrafish live longer than mice, averaging a life span of 3.5 years (and up to 5.5 years in captivity). The average life span of mice is only 2 years.
Zebrafish in research to date
Zebrafish have been well used in genetics, neuroscience, pharmacology, and toxicology research. The zebrafish has rapidly become a prominent model in behavioural neuroscience. Looking at all the major neurotransmitters and hormones that are investigated in neuroscience, they are as good a model as many mammalian species. Studies have show that zebrafish are the ideal species for testing in behavioral domains including anxiety, sleep, sociality, reward, and cognition. In addition, many popular behavioral tests that are used in rodents have been successfully translated to zebrafish studies (e.g. T-maze, plus maze, social preference, social interaction, and open field tests). What’s more, the vast variety of video analysis technology available today makes behavioural testing extremely easy to automate and collect data (Smit, 2020).
Fun facts about these social little fellows:
- Zebrafish have a natural tendency to shoal.
- Zebrafish are fantastic students, and they can show off their learning ability in a T-maze. They also demonstrate color discrimination and are able to learn to swim to a certain color.
- They rapidly develop their inner clock.
- A zebrafish usually grows to a length of 6.4 cm but in captivity, it rarely exceeds a length of 4 cm;
- Zebrafish are one of the few species of fish that has been sent to space.
- Zebrafish are most frequently used model organisms for genetic and developmental studies.
- The male zebrafish is usually slender with a torpedo-shaped body. It can be distinguished from the female by the presence of golden stripes in between the blue stripes. The female zebrafish, on the other hand, has a larger belly and silver stripes between its blue stripes.
- Some adult zebrafish possess antennae or barbels near their mouth, which are mainly used to search for food in muddy water.
- Zebrafish are omnivorous and can eat anything smaller than them. They mainly feed on insects and insect larvae, phytoplankton, and zooplankton.
- There are several varieties of zebrafish including long-finned, short-finned, albino, pink, striped, and speckled.
- Zebrafish can regenerate their fins and their heart if they get damaged.
- The minnow and carp family, to which the zebrafish belongs, is the largest of all fish families, with over 2,000 species.
- Zebrafish possess a melanin-producing gene similar to humans that can segregate between light and dark skins.
In short, Zebrafish are fascinating mammalian-type aquatic creatures that make for advantageous and favourable biomedical research models. They allow for a vast variety of research opportunities, including research in areas such as neuroscience, organ research, regeneration and vertebrate development. For more information on zebrafish research, interested readers can visit the Zebrafish Information Network (ZFIN) for a curated selection of genetic and genomic data available for zebrafish as a model organism.
Heath, J. (2020). Animals in research: zebrafish. Retrieved 8 July 2020, from https://theconversation.com/animals-in-research-zebrafish-13804
Levin, E., & Cerutti, D. (2009). Methods of Behaviour Analysis in Neuroscience (2nd ed., p. Chapter 15: Behavioral Neuroscience of Zebrafish). Boca Raton: CRC Press/Francis Taylor.
Smit, G. (2020). How zebrafish are changing neuroscience. Retrieved 8 July 2020, from https://www.noldus.com/blog/how-zebrafish-are-changing-neuroscience