What’s the deal with Master Mega, Frye’s Eels, & Big Man using ink?

In lore, I thought that the creatures to use ink were “inkfish” (as referred to by Flow), being a term for cephalopods, which would include squids (Inklings) and octopi (Octolings) in addition to cuttlefish (like Craig?) and nautiluses (I think there’s a band member who is a nautilus). as far as I know Salmonids technically use some weird slime or saliva or something, not ink. Mr. Grizz also uses ink, but he’s done so much weird stuff with fuzzy ooze that it could probably be explained away with that somehow.

For Big Man, his species are likely just one that uses ink that we haven’t heard of until Splatoon 3. One of the things that rays have in common with cephalopods is a lack of bones, which Inklings/Octolings canonically don’t have. However, sharks and eels definitely do have bones. So why do they have ink in the same way as the inkfish + rays do?