Just as a note- you seem to have left out the claspers on sharkboi. Or just made them small/not easily noticeable? Idk just biologically there should be a little bit more to the back fins to show dirk as not-female. Partially it's that I can't tell exactly what is pectoral/caudal with his fins, but that's due in part to dorsal position and he's a mermaid, so none of my accuracy stuff really matters? Idk look up claspers and the ilk, check just in case.

Let’s just… It’ll probably work differently for shark-merfolk and shark-shark.
So here’s what I’m thinking :