I said both are wrong.. BUT.. there are purposes for it depending on your reasons.
Genetically speaking, some fish are a scientists goldmine because of their properties. Zebra Danios, for example, are highly prized for some geneticists due to the fact that the first few days of their life their bodies are transparent, making it easy to study how mutations develop inside of them. This can, eventually, create advances in sciences and medicine such as gene therapy, metabolism, and finding cures for genetic defect. So, if used scientifically, humanely, and in a properly sanctioned lab, then I would say it servies its purpose.
But pretty much all other mutilations I think are wrong, personally..
There are plenty of examples of animals who have been modified.. bubble-eyes goldfish, persian cats, and pug dogs for example. They have been genetically modified and bred for defects for various reasons, and all of them can end up with health problems as a result (for a few examples in cats, breeding for short tail, ie: Manx, can lead to unnatural shortening of the spine, breeding for albinism can lead to deafness, breeding stump-nosed cats like persians can lead to cleft lip, cleft palate, nasal issues and brain disorders, breeding for polydactylism can lead to twisted appendages).
Essentially, the moral behind my reasoning is that messing around with a creatures natural growth, in short, can impair them and casue suffering.
So.. I would say, unless you can predict with ABSOLUTE certainly all of the long term effects of modifying a creature, then it is wrong to do so.
Just my 2 cents worth..
(sorry if I repated anyone elses posts.. there were too many so I did not read em all
) ..