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October 25, 2001

Saltwater Parasites

Unlike remoras that attach and release, these parasites make a permanent home on gamefish.

Q: While on a fishing trip to Mazatlan, Mexico, I photographed these three disgusting parasites attached to a dead striped marlin at the dock. They were alive and had some sort of moving, feathered claws opening and closing at the ends. What are they? Are they common? What is their life cycle and how do they affect their hosts? - Dwayne Flebbish, Salt Lake City, Utah

A: According to Ron Thune and Al Camus at the Aquatic Animal Disease Diagnostic Lab, Louisiana State University Department of Veterinary Microbiology and Parasitology, they are probably a form of parasitic copepod crustacean, possibly from the family Pennellidae.
This family includes species that are particularly harmful to fish. They burrow deeply into their host's flesh, sucking their blood and causing severe wounds and ulcers, often making the fish too repulsive-looking to market.
The life histories of some of the more than 140 species of pennelid parasites are more complex than those of other copepod families. They may pass through larval stages requiring intermediate hosts such as squid or pelagic snails, though others may be confined to a single host. The full life cycles of many species remain unknown. Some of the parasitic copepods that have adapted to permanently anchoring themselves to the body of a fish include Lernaea, Lernaeocera, Sphyrion and Pennella.
The largest of the pennelids are found in the genus Pennella, a possibility for the large parasites in your photo. Giants among parasitic copepods, Pennella filosa, for example, may reach 7 or 8 inches long with eggs sacs protruding from the ends reaching 14 inches. This genus is found frequently on the skins of swordfish, tuna, sunfish, flying fish and other pelagic species, and were reported by fishermen as long ago as the times of Aristotle and Pliny. The ancient writers described the agony of tunas and billfish jumping out of the water in efforts to dislodge the parasites.