According to an article in Practical Fishkeeping, Chairman of the HK Aquaria Mall, Alen Lee, told the Chinese newspaper Mingpao,
Firstly, we need to select the appropriate fish and use only low intensity laser beams. We only engrave on the fishes’ scales, not through them. We also had concerns over the possibility of animal abuse, but to date the mortality rate has been zero. The fishes don't even bleed.
Some experts claim that the technique is no different that the dyes used to track fish for ecological studies, while others condemn the practice as being cruel and totally unnecessary. The UK's Practical Fishkeeping Magazine has even been sponsoring a Dyed Fish Campaign since 1996.
It devalues living creatures and treats them as if they were some inanimate object that can be decorated purely for whim or commercial gain.Hmmm...I wonder what that says for human tattoos? (Although I understand that the fish do not have a choice in the matter.) If you are interested in more information, a Los Angeles TV station offers a slide show and video of some of the fish that have found their way to the States.