Sorry to chime in and add an opinion after all this has died down somewhat...but I kinda feel compelled!
The way I see it, is firstly, the production and breeding of fish for looks still incorporates some form of natural selection in operation at a basic level, natural selection being basically 'the fittest and best equipped to survive in its current surroundings' I say current, as this is the basis of evolution. Habitats change, and hence, the species has to change.
When fish are bred for looks, natural selection prohibits the production of genetically unviable offspring. They are simply aborted before development. Natures way of saying 'nope, won't work' so reason would suggest that offspring produced are genetically viable. What happens next is natural selection. Are they suitable fr the environment they live in?
We as fish keepers produce an artificial environment for our fish to live in. And so we artificially manipulate natural selection for aesthetic reasons. This is obviously not limited only to fish, any living plant or animal, including mankind, has been artificially selected for aesthetic reasons, for generations. Giving weight to the argument that our artificial selection is now effectively natural selection, but that is another argument entirely...
The problem arises when desirable traits become detrimental to the health and wellbeing of the individual bred. For example, Pug dogs being bred for flatter faces. Bad for the animals respiratory system, but a desirable trait. This trait may have been extinguished in its natural environment, but artificially, the are allowed to survive. However, the life expectancy of the individual is decreased, and therefore, becomes harder to reproduce, and extremes that are severely detrimental to the offspring will not be possible.
The real issue we have is not 'in the wild it would not happen' as we simply do not know this. We cannot be certain of the factors that would be subjected to that natural group, and thus determine its evolutionary tract.