Well, I was making more of a comment about "Gorilla-Whale" than anything.
However, if those things on his neck are actually gills, and not just different looking scales, then maybe they have another use besides just allowing him to breathe underwater; could they be a part of a system to do with his radioactive breath, like cooling vents for instance?
I always wondered why Godzilla spends most of his time underwater when he's generally considered to be mutated from a land based dinosaur; does he dwell in the sea for biological reasons to do with his radioactive nature?