Acanthocephalan: Leptorhynchoides thecatus

Volume 4, Issue 9
September 2002

Leptorhynchoides thecatus from the gi tract of a largemouth bass

Figure 1. Leptorhynchoides thecatus from the gi tract of a largemouth bass.

Hookworms belong to the Phylum-Acanthocephala which translated from Greek means “thorny-head.” Hookworms are animal parasites of many different animal species. Adult hookworms can be found in the intestines of many species of freshwater fishes.

The acanthocephalan life cycle involves the eggs being first shed by the adult worm in the fish intestine and then eaten by a small freshwater crustacean (ostracod, copepod, amphipod, or isopod).

Endysted immature hookworm

Figure 2. Encysted immature hookworm in the smooth muscle layers of a white sucker’s gi tract. This structure is called a cystacanth.

The first larval stage, acanthor, migrates through the intestinal wall of the crustacean, localizes in the body cavity and develops into the second larval stage, the acanthella. When the crustacean is then eaten by a fish, the hookworm develops into a cystacanth or develops into an adult in the fish’s gastrointestinal tract completing the hookworm’s life cycle. It is reported to take about 3 months for the hookworm to complete it’s life cycle.

Proboscis of Leptorhychoides thecatus
Figure 3. Proboscis of Leptorhychoides thecatus.

If hookworms are numerous, their hooked proboscides may inflict serious damage to the intestine; in some cases, this damage may be exacerbated by the worms’ retracting the spined proboscis and reinserting it in another place.

Hookworms have no mouth or digestive tract. They absorb nutrients directly through their body surface. Normally, adult hookworms live in the lumen of the digestive tract only, but occasionally adult worms bore through the wall of the digestive tract and come to lie in the body cavity.

Leptorhynchoides thecatus can infect many species of Maine fishes including: suckers, whitefish, salmonids, cusk, minnows, pike and pickerel, bass and sunfish , perch, smelt, and bullheads.

Special points of interest:

Fish with hookworms cannot transmit the disease to people.

Hookworms are parasitic animals.

Hookworms can harm fish by damaging the fish with their spines.

For more information read: Hoffman 1999 Parasites of North American Freshwater Fishes.


Images in this document were made possible in part by a grant from the Maine Outdoor Heritage Fund.