No model is perfect, but zebrafish are vertebrates, and therefore are more closely related to humans than commonly used invertebrate models. They are more likely to be similar to humans in many biological traits such as genes, developmental processes, anatomy, physiology, and behaviors. This is an advantage that invertebrate lab animals do not share with humans. The invertebrates are more extensively used in comparisons at the cellular or biochemical level of organization where they share many features with humans.
Zebrafish have features that make them easy to maintain, manipulate, and observe in the lab. They do well in many environments, and their small size, their ability to be kept together in large numbers, and the ease with which they can be bred makes them a favored model. Females lay a large quantity of eggs (100-200 embryos per mating). This is advantageous because for many types of genetic analysis, many embryos at different stages need to be examined to understand the problem associated with a given mutation. The embryos are fertilized and develop outside the mother’s body, are transparent, non-adhesive, and develop quickly and can be physically manipulated. Zebrafish embryos are also smaller than many vertebrate embryos and contain fewer cells, therefore, it is easier to trace the development of individual cells.