Because they are easy to observe and many of their organs are like those of humans, zebrafish are an informative model of embryonic development and genetic disease. Image © Understanding Animal Research.
Computers cannot replace animals, but they can reduce the number of animals needed. Researchers build computer models based upon what they already know about biological processes and use the models to predict what may happen under a different set of circumstances. But living organisms are far more complex than any computer model we have today. Computer modeling speeds new discoveries and reduces the numbers of animals needed. Nevertheless, animal studies are still needed to provide real-world data about what actually happens.