Custom goldfish tattooing is one pet hobby that would definitely require some patience and skill. As a child, my family had a cat that always seemed to make its way into a sewer before coming home. My mother tasked me with the job of giving the cat a bath--a feat that pales in comparison, I would think, to tattooing a goldfish! I suppose if you catch them in the fishnet you could immobilize them, but it would be difficult to keep from injuring the fish in the process.
According to the blog at nrcnext.nl, the tattoo images are created with lasers. And as to whether the fish are injured in the process, pet shop owner Alen Lee tells the blog that since the laser is a weak one, the fish feel nothing.
For some reason, that doesn’t make me feel better…