Ran up a basic 3D version of the fish just to get the form down, going to re-topologise a subdivision version over the top of this
Body is subdivided cube smushed around with sculpting tools, teeth and fins are plain polygon modelling
Added to Sketchfab with a little animation, textures via Krita. Figured it was time to stop messing about with this daft fish and get back to the Human skeleton I was making. Tasteful colours? Nah not my style!
Made an orthographic template, might adjust the proportions as I'm going. The film skeletons have slightly cartoony proportions (which I like). I think I can probably get away with poly/sub-D modelling the postcranial part but we'll see.
The skull needs a base sculpt though, made this rough one and it'll do for retopo-ing over. I'm aiming for a mean looking face (similar to Harryhausen's version) so it looks like it's coming to get you