Creating and studying transgenic fish helps researchers learn more about how they develop so that bigger, healthier fish can be produced for aquaculture. It also helps further understanding about how more complex animals like humans develop and grow. When a new gene is added, it doesn't always work as desired. It may not work at all. Unwanted side effects sometimes occur.
Promoters are just as important as the genes themselves.
Through his research on zebrafish, Danio rerio, Hackett and his students have discovered several gene controllers that work best for turning on genes to the proper level. The second problem is that regulators from the normal genes in a chromosome can affect the transplanted gene, and controllers from a transplanted gene can conflict with regulators that are already there. Insulators, or border elements, are needed to keep their functions separate.