I recently met a marine biologist involved in the fish farming industry, specifically in Scandinavia where fish farming is more advanced than most of the world. He raised an issue I had never really considered regarding fish farming; what affect does fish farming have on the wild inshore/oceanic environment? As a farming style it is very new <50 years, and the farming of many fish species like cod (i.e. not salmon and shellfish) is even younger. Traditional pastoral farming is hundreds if not thousands of years old and the affect it has had on the terrestrial environment is massive. Pastoral farming has had a great homogenising affect on the landscape. Large scale fish farming could have the same affect, and the process by which it could occur is already happening. The process is escape, not only of adults getting through holes in the net or cage but the fish spawning (mass release of eggs and sperm into the water) . Spawning of the caged fish could have two main affects; an unnatural increase in wild fish numbers resulting in the decimation of their own (and other species) food sources; a sudden swing in the genetic diversity of the natural population (as farmed fish are selectively bred). Both cause homogenisation and the loss of biodiversity just like terrestrial farming.