It is sad what kinds of things are done in the pet trade to make a little extra money.
The most egregious of these practices is probably the injection of color into fish like Parambassis baculis (or Chandra ranga), the painted glass "tetra" (it is actually in the perch family). These fish have naturally transparent bodies, and some shady fish suppliers take advantage of this fact and inject fluorescent paint into their bodies in an effort to make them more attractive to unsuspecting consumers. These consumers are then convinced that these forms are natural color morphs, bring them back home, and then wonder why their fish are dying. To this day, I have yet to see a single painted glass fish that didn't have some signs of ich or fin rot... they are often dipped in a caustic agent to remove/prevent regeneration of their stress coat, their number one line of defense against disease (getting rid of the stress coat makes them retain the irritating paint longer in their bodies, but it will eventually fade in time, if the fish don't die of disease first). "Fruit loop" tetras, some colored botias, and a few other fish are also artificially dyed or injected in the same manner, so consumer beware. These are not to be confused with fish which have naturally outrageously colored bodies, such as neon tetras, cardinal tetras, glolite tetras, green tiger barbs, bettas, and many others.
"Questionable practices" also includes some breeding practices that push fish into really unusual, unnatural body forms...some extra long finned varieties can hardly swim, roly-poly pot-bellied varieties are prone to digestive disorders and many specialized breeds are no longer nearly as hardy as their wild ancestors and have frequent genetic defects (such as spinal curving, partial blindness, infertility and lowered immunity) because they have been inbred so much.
Of course, almost all the fish we keep are no longer wild caught (probably a good thing, considering how delicate some of their natural environments are) and most are genetically manipulated to create fancy forms and bright colors, but there is a difference between a conscientious breeding program to produce a variety of a certain color pattern, or slightly longer fins, and a program which creates a severely deformed body shape that interferes with how a fish lives on a day to day basis. My friend, for example, has a large 10 year old lionhead goldfish with a huge growth on its head which is increasing in size as it ages. It has gotten to the point where it has grown completely over its eyes and it can no longer see to eat, and it is slowly starving to death because of this (some lionheads with less developed growths do not have to succumb to this fate). Other extreme examples include blood parrot cichlids, which are actually the artificial hybrid of 3 cichlid species, often dyed with red coloration, and butterfly discus, which are bred not to have tails (this makes it very difficult for them to swim).
There is a reason why evolution pushes for certain body shapes and structures, eliminating others--we should try and appreciate fish not for the gaudiness we can create, but for their natural beauty which combines form so well with function.
Anyway... this is just a quick comment to inform people of what's going on, not to criticize anyone who owns these fish--the types you decide to buy are your own business. Obviously, the home aquarium is sheltered and very different from the wild environments the ancestors of these fish came from, and should accordingly be treated differently. The level of modification we each think is OK is a personal choice... I am not a purist who is pushing for everyone to keep all goldfish that look like carp or all dogs that look like wolves. Whatever fish you get, "doctored" or not, please do some background research on their care and behavior. What's done is done... don't feel bad if you own "politically incorrect fish".. just do all you can to learn about their care now, and try not to support the practices that deformed them to begin with in the future.