I usually disagree with genetic engineering and this is no exeption to that rule, but I do believe GE can be of some good. For example, scientist can now look at the Dna of you babies and check that it is "right" if they find that your son/daughter is going to suffer from a life threatining illness that specific gene can me modified to be correct.
However in the context of this converstaion I think it is wrong because the GE is purely done to create a fish that looks "better" (Ps. I dont think they look better)
A rule which I always abide by is EQUALITY, has humans we are equal to every other living thing in this world and that if we are prepared to do something for anything living we should be prepared to do it to ourselves.