The zebrafish has a number of unique characteristics that makes it a fantastic species for investigating vertebrate development and for modelling human disease.
The transparency of zebrafish embryos has become one of the leading reasons for using them for scientific research. Being able to see through the embryos allows us to watch the morphological changes that occur during development. Cells move around, organs form, the heart starts to beat and all of this is visible in the living embryo. (movie of heart beat) This transparency also means we can make use of a naturally fluorescing protein called GFP (Green Fluorescent Protein) – which can be used to label individual cells, organs or even organelles.
To look at how embryos develop in normal and abnormal situations (such as when genes are mutated or drugs are added to the water) we need access to many eggs. Luckily the zebrafish adults are small, around 3-5 cm in length, and like to be kept together in shoals. The fish also lay eggs readily, meaning we have a good supply of embryos for our research. In the wild they thrive in quite murky environments, like rice paddies and the Ganges. Therefore they are very hardy and easy to maintain in our aquria.
The female fish lays her eggs in the water around her, where they are fertilised by the males, allowing us to collect the eggs as soon as they're laid. This is important as it means we can examine what is happening and manipulate the embryos from the moment they are fertilised.
They develop from a single cell in a fertilized egg to something that resembles a tiny fish in 24 hours – for a mouse this process takes around 21 days. When they are around 4-5 days old the embryos become swimming larvae and start to catch their own food.
Mutations can be generated and analyzed to see what happens when a gene’s normal function is altered. Genetic screens, which involve looking at lots of different mutated fish are often the most effective way of identifying new genes or discovering novel functions of known genes. Discoveries can also be made by manipulating genes with chemicals.
Zebrafish are more closely related to humans then invertebrate models such as the worm C. elegans and the fly D. Melanogaster, and they offer all the advantages described above over other vertebrate models such as the mouse and chick. Therefore they provide an excellent system to investigate human disease and development.