Sony Alpha 7C II
So I hesitate to post this, because I'm not a camera expert. I only know the basics, but I have access to the above camera. It didn't do well for me at first, but then I changed lenses. Honestly, I'm a hack at this, and literally with just a few minutes of fiddling, and I had one of the better aquarium pics I've ever taken.
If you Google it, you'll see it's not an entry level camera or price, but I wanted to back up the people who are suggesting Sony Alphas.
I'm not posting the pic. I will eventually. If you've seen my journal, you know I've been having an algae nightmare. I think I'm I'm back on top of things (I hope) and plan to post pics eventually when everything is turned around. Right now I'm in the annoying time and patience stage of the recovery.