GM varieties of fish have already been commercialised in some parts of the world, intended including to grow faster and reach a bigger size. This practice is not applied in Belgium yet. Whereas those fish are supposed to be raised in confined areas, drastic measures should be taken to prevent those varieties from escaping into the wild. After all, some GM varieties of fish have already been shown to threaten the future of the species when they come into reproductive contact with the wild related members. Furthermore, GM fish could threaten local species and ecosystems through their invasive behaviour.

Similarly for other marine GM products, the consequences of interbreeding and competitive behaviour with wild relatives should be carefully investigated and, as a rule, should be avoided at all cost. The Belgian Marine Environmental law prohibits the deliberate introduction of genetically modified organisms.

Specific attention needs to be given to side effects of genetic manipulations aimed at increasing the size of commercial species (amplification of growth hormone gene).