Being a biology student and ardent Neodarwinist, I feel obliged to share a bit of knowledge about the problem of inbreeding (or its close cousin, linebreeding). The reason inbreeding is problematic is not that it distorts genetics, or poisons a gene pool or anything. It does nothing of the sort. The problem lies in the fact that everyone (you, I, and yes even your stingrays) carries a few very rare but dangerous recessive genes.
These genes are, by definition, rare in the gene pool. If they were to become more common, they would be weeded out by natural selection (as they would pair up, as per Gregor Mendel's discoveries, as an expressed recessive-recessive combination). So these rare genes almost never come into play, and are harmless when held in-check by a dominant and more beneficial allele.
With a rudimentary knowledge of Mendelian genetics, it is easy to see why inbred specimens exhibit genetic "defects". The gene pool remains pure, but sometimes these recessive genes are expressed. This could produce anything from a stillbirth (as even
Homo sapiens, on average, carries on average 2 absolutely lethal genes per individual) to strange variations in appearance, physiology and behavior.
The change could be something as benign as albinism to something as serious as not possessing gills or skin.
The gene pool is perfectly fine, and in fact if the F1 specimen is fertile, its offspring will be absolutely unaffected by the inbreeding (given that the mate doesn't also posses the rare recessive trait, but this is unlikely yet possible with any sexual reproduction).
The key question is, I believe, an ethical one. Is the desire for a new, exciting trait worth the possible suffering of the offspring in question? Many types of domestic animals (livestock such as pigs and cows, as well as pets such as dogs and cats) have been produced by the application of this technique. Without the deliberate application of inbreeding/linebreeding, the traits may never manifest. At the same time, you may cause the unnecessary suffering of the offspring that you are trying to produce.
I hope this clears the water up a bit on the subject.
