I rescued my pleco from an LFS 10g sump, where there was brown froth all over the top. IMO it's;
Goldies; goes without saying, feeders and bowls are such cruelty
Blood Parrots; mutilated with cut tails, dyes, etc. They're magnificent fish. Not my cuppa, but neither are datnoids and arowana, and they don't deserve that treatment either.
Anything that eats algae: Plecos, CAEs and ottos all take this abuse. Algae isn't dirt. Poor fish.
Lower Price Large Fish: RTCs, Pacu and Oscars fall into this category, anything under 20$ and gets over a foot is heavily abused.
Livebearers: Anyone who's given birth knows how much it sucks to be one of these girls.