Rashi wrote that only the flesh of unclean fish are unclean, while the bones, fins, etc, may be eaten. God said not to eat or touch their carcasses, though, and I can't see how their fins and bones aren't part of their carcasses.

Remind me again why anyone cares what Rashi had to say.

OTOH, at some point, all of that stuff essentially becomes dirt, like diatomacious earth. You'll have to figure out for yourself where that line is.