This one sucks because I think it isn’t unknown, but easy to ignore. The worst thing I’ve seen related to this was the other day. Someone posted a video of a barn during ventilation shutdown for culling pigs and it was one of the most barbaric things I’ve seen. It was like something from a death camp.
tbf you are also having humans abused and hurt for you. Prisons to remove inconvenient people from society, wars over resources and power, and slavery overseas to produce goods at low cost. Even if you go vegan, you're still complicit in unspeakable crimes against humanity as a member of society.
That's fair. But if that's your goal, you'd be better off working to end the government subsidies on meat and dairy that exist solely so people will eat more meat, rather than wasting time trying to eliminate every bit from your own diet. If we managed to remove those subsidies, the price of meat/dairy would quadruple and millions of animals would be saved from consumption. Not to mention people would probably be healthier too.
While some say the debate is not settled, I believe there is ample evidence to say that fish do indeed feel pain. You can find literature in the source above.