This has been coming up a lot, so I want to discuss the implications of this research  and others concerning whether or not fish feel pain. Citations below the cut if you want them.
First of all, it’s all based off of research and compiled articles, not actual experiments. It’s based upon things scientists generally agree upon. Such as because mammals experience pain in the neocortex and fish don’t have one, they can’t possibly feel pain.
However, new experiments by a different scientist (not funded by an institute invested in the outcome), found that even without a neocortex, crustaceans and molluscs nursed and held wounds like they still felt it, long after the wound healed.
My favorite quote is, “Without a neocortex, one would assume, an individual could not experience pain, but it turns out that crustaceans’ nervous systems are wired a little differently than our own: they lack the visual cortex than humans have, but can still see. So can crustaceans suffer without what we believe to be the requisite parts?” 
Another experiment found that rainbow trouts exhibited strange behavior when injected with bee venom, as if they were in conscious pain. Such as rubbing the wound against gravel.
To conclude, fish may feel pain differently from humans, but that does not mean they do not suffer or feel that pain. They do.
So stop trying to excuse not taking care of the pet you voluntarily adopted with, “They don’t feel pain!”