Tattooed fish
The practice we as fish keepers should be angered by the most. Beyond our years of domestication of other fish, and the horrible treatment of feeder fish, or even pretty much keeping fish in bowls, this is the closest acceptable thing in this hobby that most sane fishkeepers consider animal abuse. This is, the act of tattooing fish.

Not glofish
Alright, so a lot of people mix up tattooed fish and glofish. In all honest, glofish aren’t torture breeds. They’re just not in any way natural looking. They’re many variants now, but we’re originally made by mixing the dna of jellyfish with danios. What tattooed fish are is when a color is directly printed onto a fish.

Is it painful
While it is hard to attribute pain to a fish in the way it is with other animals, there is no way this action could be considered harmless. The first sign is the severely shortened lifespan, and the high frequency of stress shown in these fish. They typically end up dying from internal parasites, due to them being easily stressed and being susceptible. The second sign is that tattooed are still painful for humans, so there’s no way it wouldn’t be harmful on a fish. I’ve heard people say it’s a one and done deal, and it only takes a second, but if that were true, human tattoos would be so much faster.

A younger audience
A major argument I’ve seen for fish like these is to think of the younger generations. People say that if a five year old finds a molly with a heart painted on its chest in bright pink, and likes the fish, that will get them into fish keeping. The main argument for why people say this is acceptable is become people feel that the aquarium hobby is dying off. While there is something dying off, it isn’t the hobby, but the fish being put through such animal abuse. If a child becomes interested in a fish just because they have a little heart painted on their scales, and not for the fish underneath, they’re more likely to care for that fish incorrectly.

Conclusion
This, by far, is the worst things humans have done to fish. Though, it may be appealing to little kids, nothing can beat the pure beauty of a well put together fish tank, with healthy fish. What tattooing does to a fish is severely shorten it’s lifespan, and most likely doom it to a person who won’t take care of their fish.