Dactylogyrus is a genus of tiny (less than 2 mm long) trematode worms which spend their lives anchored to their host fish's gills. Worms attach to the gill tissue using specialized hooks on the rear end of their bodies, leaving the mouth end free to forage on gill tissue.
Mature worms release eggs each day; these sink to the mud and within a few days hatch into free-swimming larvae with a hankering for fish mucus and a time limit in which to find it. They have only about 4 to 6 hours to get pulled into a fish's mouth and grab onto its gills before they lose the ability to swim.
Reference/Image from: Paperna, I. 1996 Parasites, infections and diseases of fishes in Africa. An update. CIFA TECHNICAL PAPER 31
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