zebrafish
The zebrafish is a small striped freshwater fish that has become a favourite vertebrate model because its embryos are transparent and develop outside the mother. You can watch a beating heart form, blood vessels sprout and a brain take shape in a living embryo under a microscope, all within a day or two of fertilization.
Zebrafish combine advantages usually split between simple and complex models: a female lays hundreds of eggs at a time, allowing large genetic screens, yet the animal is a true vertebrate with a backbone, heart, blood and brain organized much like ours. This makes it especially valuable for studying how vertebrate organs and tissues form and how birth defects arise.
Their genes can be readily altered or silenced, and fluorescent markers can light up chosen cells so their movements can be filmed in real time. As a result, zebrafish bridge the gap between invertebrate models like flies and worms and mammalian models like mice, offering vertebrate biology in a transparent, fast-breeding package.
Because the embryo is clear, researchers can use a fluorescent label to make blood vessels glow and watch, frame by frame, how a circulatory system is wired during development.
A see-through vertebrate embryo developing before your eyes.
Zebrafish can regenerate parts of their heart and fins, so they are also studied to understand why mammals heal such injuries with scars instead of new tissue.