Making a "fish" actor that would float around?

I wanna make fish NPCs that pretty float, which would look like they would swim underwater. Could someone tell me how to make basic movement?

It's supposed to be a basic actor that cannot attack.

You could probably start by duplicating the Lost Soul and removing its attack function.

Those things more-or-less look like they're floating through air as if it were water to begin with. I don't think you'd need to modify their movement data too much to get your intended result.

Holy crap, you've got no custom title. 8-0

It depends upon what platform and if you want to use DEH, BEX, ACS, or fragglescript.

Phobiata.wad has some nice floating fireflies in the opening sequence.
It uses fragglescript and some modified object (DEH I think).

Thanks, guys. I'll try your options. :)