Commercial breeders of tropical fish have adopted many of the scientific breakthroughs in genetic manipulation, and have come up with quite a few fish that exist nowhere in nature. Some folks deride these fish, and call them “Frankenfish.” I have a different opinion. I applaud what these fish breeders have been doing in coming up with new aquarium fish (as long as we are not talking about painted, dyed or tattooed aquarium fish).
Probably the best-known, genetically manipulated fish is the “GloFish,” which is a plain old zebra danio that has had genes from a coelenterate spliced into its genes. This makes for “fluorescent” fish in bright colors, including red, green and yellow. The breeding and distribution of GloFish is controlled by license in the U.S., and presumably, the fish are sterile, as I do not know of anyone who has bred them.
Other genetically-new aquarium fish include hybrids of two different species of fish. The most-recognized hybrid is the “parrot” cichlid. In addition, new hybrids of large catfish (red tailed, shovelnose, etc.), recently became available. The hybrid parrot cichlids are, unfortunately, often dyed and/or tattooed, but the unblemished ones in different natural colors are quite nice. The catfish hybrids are smaller than either of their parents and they are interesting-looking fish.
When it comes to genetically manipulated aquarium fish or a hybrid of two species of fish, a number of “purists” out there find them repulsive. These fish hobbyists believe that nothing like this should be done to fish. This is, to my way of thinking, a pretty silly position to take. I see very little difference between physically playing with the genes of fish and selectively breeding for certain traits. And when it comes to hybrid fish, hobbyists should be aware that swordtails, platys and mollies all originally come from hybrids, and surely no one would want to exclude those fish from the fishkeeping hobby.