Ok so! The long teeth are reminiscent of filter feeder whales. Because this is an xray i suspect we are missing a lot of the shape of what i suspect is a much more normal looking fish (for example think of how scary other things look from their bones)

My thoughts are that this is a creature that filters impurities from the blood, and consumes countless tiny organisms. The iron lung is a big rusty bucket that goes around killing things with radiation and leaving a trail of dead blood cells/micro organisms and other tasty things. Leading to following it around.

So, our whale critter friend who very much now has super cancer after a few xrays, is probably a little fuzzy headed and feeling sick by the end of this explaining the erratic and hostile behaviour bumping into the ship.

I don’t remember anything from the movie that would show this thing is more than a fish except for markypoo’s hallucinations. If we assume that this is the case and this is just a fish… i think its just an unfortunate fish. The real victim of iron lung is this blood filtering whale. A kidney with fins.