Underwater Trout animation

Hi, a couple questions for those more knowledgeable than myself. I would really like it if someone could point me in the right direction.

I’m looking to do an underwater animation of a trout swimming around.

First, what would be the best way to do the fins to make it look as fluid/realistic as possible?

Also, I’ve never done anything underwater, if someone could lead me in the right direction, i would really appreciate it.