Anchor headworm disease. Female anchorhead worms are parasites that are easily identified by their appearance when they cling to the body of a sapphire fish. They reach a maximum length of about 20 mm in spring when two oocysts of about 3 mm form at the free end of the body.

Short-term soaking in 3% salt solution can also remove worms from fish removed from the body. There are now aquarium treatments that kill the adults. Also in ponds, repeated use of the antiprotozoal treatment can kill the larvae. Adult worms can also be killed with trichlorfon.