That is the exact reason that bottom dwellers are not common in sushi - as i understand it - most worms are considered nematoads or something along that line - common in lings, halibut, some rockfish etc. They can be extremely detrimental to ones heath if consumed, by cooking them you kill them and their eggs. I have read that halibut sushi is often frozen first to kill off these little buggers. Just look for them when you clean the fish, and remove them. If cooked they are just a little extra protein.