With those hands, I’d say it’s probably a mole.

https://northernwoodlands.org/outside_story/article/shrew-or-mole-mouse-or-vole

Cat time.

Can't imagine how a mole - a mostly subterranean creature - would wind up indoors and in a fish tank. They never travel very far at all from their extensive tunnel system and I have never heard of one being found inside a structure, ever. Ditto shrews (although the photo does resemble one). And the ability to wind up in a fish tank shows some acrobatic skills I'm not sure either possess.

I agree that a cat could take of the issue handily regardless of the animal in question. Or you could try trapping or baiting (not sure what one uses for baiting a mole.....worms??).

Short tail shrew is what it looks like to me. For some reason, we have been getting them in the house this winter too, a first for us here. Been an unusually high mouse winter too. We got a big hunter cat that brings me presents, so I get to ID when it's a shrew or a mouse, lol. I thank him and give him treats and sigh- lots of these critters usually means a bad tick summer is coming.

Shrews are carnivores- and yep, they do like fish. It might have been going for a drink if you don't have open water like pet dishes sitting out or toilet lids up. If you used to have mice, shrews eat them too and then will move right on to the old mouse home. Shrews are good climbers like mice are, so it's not out of the question to find one in a fish tank.

You can try live traps or kill traps for chipmunks and rats in the house if you think you got more of them. Like mice in the house, if there's one, there's usually more. Peanut butter is supposed to be a good bait, some folks say mix it with oatmeal. Outdoors you can try setting out coyote urine baits as repellent, or commercial repellents noted for this kind of critter. Bucket traps can work too outdoors if you use the spinning can on a dowel trick. Up to you if you want to live trap or drown them.

My shrews don't look like this guy, but I'll take your word for it. Makes sense that it was looking for a drink! I was wondering how it knew there were fish in the tank. lol!

Shrew that likes sushi maybe?