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Miscellaneous Parasites of Fish
by Robert B. Moeller Jr., DVM

California Animal Health and Food Safety Laboratory System
University of California

Lernea Anchor worm (Also Salmincola and Lepeophtheirus spp.)

  1. Copepod
  2. Infects all freshwater fish and is a serious problem in cyprinids (bait minnows, goldfish, and carp).
  3. Clinically the parasite invades the skin, usually at the base of a fin. The head develops into an anchor that holds the female in place. The female then develops egg sacs (two finger like projections attached to the end of the body). The ulcers are slow to heal.
  4. Other copepods such as Ergasilus sp. are found on the gills and cause serious gill damage.

Argulus - Fish louse (Branchiura)

  1. Parasite of the skin and occasionally buccal cavity.
  2. Cutaneous ulcers due to piercing of epidermis by the retractile preoral stylet (a proboscis-like mouth) for sucking blood from the fish.

Gyrodactylus sp.

  1. Monogenetic trematode; flattened and leaf-like, no eyespot, cephalic end V shaped, has an attachment organ (haptor) and two large anchors with 16 marginal hooklets.
  2. Affects most species of fish.
  3. Fluke anchors itself to skin, fins, and gills that may cause excessive mucus secretions over gills and skin. Fish may undergo flashing and have fraying of fins. Severe infection (gills) may cause the fish to become dyspneic and die.
  4. Life cycle is direct. The larva are released and attach almost immediately to the host.


  1. Monogenetic trematode; flattened and leaf-like, four anterior eyespots, cephalic end scalloped, ova present, has an attachment organ (haptor).
  2. Affects most freshwater species, particularly carp and goldfish.
  3. Fluke anchors to gills causing excessive mucous secretions, and frayed edges. Fish become anoxic with flaring of the gill opercula.
  4. Life cycle is direct. The adults are oviparous and produce eggs with long filaments. The eggs are usually attached to the gills. The eggs develop into a onchomiricidium that then attaches to the fish.

Diplostomum spathaceum (Eye fluke)

  1. Digenetic fluke; metacercaria is infective state in fish.
  2. Gulls and pelicans are the definitive host. Snails (Lymnaea sp.) are the first intermediate host. Fish (salmonids) are the second intermediate host.
  3. Clinically, the metacercaria are presented as white dots; later the eye becomes opaque. Blindness occurs in severe infections. The metacercaria are found in the anterior chamber, vitreous body, and lens causing cataracts.

Uvulifer ambloplitis (Black spot disease)

  1. Digenetic fluke; metacercaria infect fish.
  2. Herons and kingfishers are the definitive host, snails are the first intermediate host. Fish are the second intermediate host.
  3. Clinically the fish have numerous black to brown spots up to 1 mm (dia) over the skin, gills and eyes. The spots contain a metacercaria surrounded by heavily pigmented fibrous connective tissue.

Acanthocephalus (Thorny headed worm)

  1. Pomphorhynchus sp. and Acanthocephalus sp.
  2. Acanthocephalans are observed in many species of fresh water and marine fish. Adult parasites live in the intestine. The larval second intermediate stage may encyst in the liver, spleen or mesentery.
  3. Heavy infections are observed in feral fish. Infected fish may not show signs. However, some fish are emaciated and have swollen abdomens. In heavy infections, raised subserosal nodules may be observed in the gut. These nodules may have the proboscis attached. Histologically, a severe granulomatous reaction is associated with the nodules. If the parasite penetrates the serosa, a peritonitis may occur.
  4. The life cycle is complex; an amphipod is the first intermediate host. In the amphipod, the acanthor develops into a cystacanth. Small fish are believed to be the second intermediate host (paratenic host) for the cystacanth. The life cycle is then completed with the ingestion of the cystacanth and development of the adult worm.


The parasite causes little problem in fish. However, in man, it can be a serious public health threat. Brown and white larva (third stage) are observed in the viscera and musculature of fish. Many marine mammals are the definitive host with this nematode living in the stomach.
Eye Plant Petal Tints and shades Font


1. Roberts R.J: Fish Pathology, Bailliere Tindall, London, Second edition, 1989.

2. Ferguson H.W.: Systemic Pathology of Fish, Iowa State Press, Ames, Iowa, 1989.

3. Anderson B.G.: Atlas of Trout Histology, Wyoming Department of Fish and Game, 1974.

4. Fox J.C.: Laboratory Animal Medicine, Academic Press, 1984.

5. Magaki G., Rebelin W.E.: The Pathology of Fishes, The University of Wisconsin Press, 1975.

6. Wolf K.: Fish Viruses and Fish Viral Diseases, Cornell University Press, London 1988.

7. Tucker C.S.: Channel Catfish Culture, Elsevier Science Publishers, Amsterdam, 1985.

8. Principal Diseases of Farm Raised Catfish, Southern Cooperative Series Bulletin No 225, 1985.

9. Wales J.H.: Microscopic Anatomy of Salmonids. An Atlas, United States Department of the Interior, Resource Publication 150, 1983.

10. Grizzle J.M.: Anatomy and Histology of the Channel Catfish, Auburn Printing Co, 1976.

11. Reichenbach-Klinke H. H.: Fish Pathology, T.F.H. Publications, Inc. Neptune City, NJ. 1973.

12. Stoskopf, M.K.: Fish Medicine, W.B. Saunders Co. 1993.

13. DeTolla, L.J., Srinivas, S.: "Guidelines for the Care and Use of Fish in Research". Institute of Laboratory Animal Resourses Journal. Vol 37:4(1995), pp 159-173.

14. Kane, A.J., Gonzalez, J. F., Reimschuessel, R: "Fish and Amphibian Models Used in Laboratory Research". Laboratory Animal. Vol 25:6(1996), pp 33-38.

15. Lewbart G.A. Self-Assesment Color Review of Ornamental Fish, Iowa State Press,1998.

16. Bruno D.W., Poppe T.T., A color atlas of Salmonid Diseases. Academic press, 1996.
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