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Common Freshwater Fish Parasites Pictorial Guide: Crustaceans

Deborah B. Pouder, Eric W. Curtis, and Roy P.E. Yanong

Introduction

This publication is one in a series of pictorial guides that is designed to assist in the identification of common freshwater fish parasites. The publications included in this series are:

  • Common Freshwater Fish Parasites Pictorial Guide: Sessile Ciliates
  • Common Freshwater Fish Parasites Pictorial Guide: Motile Ciliates
  • Common Freshwater Fish Parasites Pictorial Guide: Dinoflagellates, Coccidia, Microsporidians, & Myxozoans
  • Common Freshwater Fish Parasites Pictorial Guide: Monogeneans
  • Common Freshwater Fish Parasites Pictorial Guide: Digenean Trematodes
  • Common Freshwater Fish Parasites Pictorial Guide: Nematodes
  • Common Freshwater Fish Parasites Pictorial Guide: Acanthocephalans, Cestodes, Leeches, & Pentastomes
  • Common Freshwater Fish Parasites Pictorial Guide: Crustaceans

The information provided in this guide is not intended to be a complete, detailed description of each parasite or parasite group and its characteristics but rather is intended to assist in the visual identification of some of the most common species or groups of parasites seen in freshwater fish. For further information on each parasite, refer to publications in the "Recommended Reading" and "Reference" sections below.

Guide Information

  • Target Tissue: provides the location on/in the fish where the parasite is most commonly found.
  • Characteristic: provides a brief description about the appearance of the parasite.
  • Size: provides the size or size range of the parasite. (1 µm = 0.001 mm = 0.0001 cm) (µm = micron or micrometer; mm = millimeter; cm = centimeter)
  • Movement: provides the type of movement, if any, of the parasite.
  • Note: provides a brief comment of interest about the parasite.

Crustaceans

Argulus ("Fish Louse")

Target Tissues: Skin, fin

Appearance: Flattened, saucer shape; two suckers; two eyespots

Size: Juveniles approx. 1–3 mm in length; adults approx. 5–20 mm in length

Movement: Free-moving; may glide over fish when feeding

Note: Can be seen with unaided eye; common in koi and goldfish; sucks body fluids from host; egg-layer (requires multiple treatments)

Ergasilus

Target Tissues: Primarily gills

Appearance: Conical, segmented body with grasping antennae

Size: Usually greater than 2 mm in length

Movement: Generally seen fixed (attached with grasping antennae) on fish

Note: Direct life cycle; often incidental on fish but modified antennae used to grasp fish can cause severe, localized damage and infection

Lernaea ("Anchor Worm")

Target Tissues: Skin, fin

Appearance: Long, narrow; "anchor" at one end imbeds into fish; pair of egg sacks often seen at end opposite of anchor

Size: Approx. 5–25 mm in length

Movement: Generally seen fixed (attached with anchor) on fish

Note: Only females are parasitic; can cause secondary bacterial infections due to wound from anchor; common in koi, goldfish, and golden shiners

Acknowledgements

The authors thank Christine Densmore for the photograph she contributed to this publication.

Recommended Reading

UF/IFAS Circular 91 Nematode (Roundworm) Infections in Fish. https://edis.ifas.ufl.edu/FA091

UF/IFAS Circular 120 Fish Health Management Considerations in Recirculating Aquaculture Systems - Part 1: Introduction and General Principles. https://edis.ifas.ufl.edu/FA099

UF/IFAS Circular 121 Fish Health Management Considerations in Recirculating Aquaculture Systems - Part 2: Pathogens. https://edis.ifas.ufl.edu/FA100

UF/IFAS Circular 122 Fish Health Management Considerations in Recirculating Aquaculture Systems - Part 3: General Recommendations and Problem Solving Approaches. https://edis.ifas.ufl.edu/FA101

UF/IFAS Circular 920 Ichthyophthirius multifiliis (White Spot) Infections in Fish. https://edis.ifas.ufl.edu/FA006

UF/IFAS Circular 921 Introduction to Fish Health Management. https://edis.ifas.ufl.edu/FA004

UF/IFAS Fact Sheet FA-13 Use of Copper in Freshwater Aquaculture and Farm Ponds. https://edis.ifas.ufl.edu/FA008

UF/IFAS Fact Sheet FA-90 Pentastomid Infections in Fish. https://edis.ifas.ufl.edu/FA090

UF/IFAS Fact Sheet FA-107 Common Freshwater Fish Parasites Pictorial Guide: Sessile Ciliates. https://edis.ifas.ufl.edu/FA107

UF/IFAS Fact Sheet FA-108 Common Freshwater Fish Parasites Pictorial Guide: Motile Ciliates. https://edis.ifas.ufl.edu/FA108

UF/IFAS Fact Sheet FA-109 Common Freshwater Fish Parasites Pictorial Guide: Flagellates. https://edis.ifas.ufl.edu/FA109

UF/IFAS Fact Sheet FA-110 Common Freshwater Fish Parasites Pictorial Guide: Dinoflagellates, Coccidia, Microsporidians, and Myxozoans. https://edis.ifas.ufl.edu/FA110

UF/IFAS Fact Sheet FA-111 Common Freshwater Fish Parasites Pictorial Guide: Monogeneans. https://edis.ifas.ufl.edu/FA111

UF/IFAS Fact Sheet FA-112 Common Freshwater Fish Parasites Pictorial Guide: Digenean Trematodes. https://edis.ifas.ufl.edu/FA112

UF/IFAS Fact Sheet FA-113 Common Freshwater Fish Parasites Pictorial Guide: Nematodes. https://edis.ifas.ufl.edu/FA113

UF/IFAS Fact Sheet FA-114 Common Freshwater Fish Parasites Pictorial Guide: Acanthocephalans, Cestodes, Leeches, and Pentastomes. https://edis.ifas.ufl.edu/FA114

UF/IFAS Fact Sheet VM-104 Cryptobia iubilans in Cichlids. https://edis.ifas.ufl.edu/VM077

References

Hoffman, G. L. 1999. Parasites of North American Freshwater Fishes. Ithaca, NY: Cornell University Press.

Longshaw, M., and S.W. Feist. 2001. Parasitic Diseases. Pages 167–183 in W.H. Wildgoose, editor. BSAVA manual of ornamental fish, second edition. British Small Animal Veterinary Association, Gloucester, England.

Noga, E. J. 1996. Fish Disease: Diagnosis and Treatment. St. Louis, MO: Mosby-Yearbook, Inc.

Stoskopf, M. K. 1993. Fish Medicine. Philadelphia, PA: W. B. Saunders Company.

Woo, P. T. K., editor. 1995. Fish Diseases and Disorders, volume 1: protozoan and metazoan infections. CAB International, Wallingford, United Kingdom.

Publication #FA-115

Release Date:March 11th, 2020

Reviewed At:February 12th, 2024

Related Experts

Yanong, Roy P.

Specialist/SSA/RSA

University of Florida

Pouder, Deborah B

staff

University of Florida

Related Topics

Fact Sheet

About this Publication

This document is FA-115, one of a series of the School of Forest, Fisheries, and Geomatics Sciences, Program in Fisheries and Aquatic Sciences, UF/IFAS Extension. Original publication date July 2005. Visit the EDIS website at https://edis.ifas.ufl.edu for the currently supported version of this publication.

About the Authors

Deborah B. Pouder, coordinator of research programs and services; Eric W. Curtis, former biological scientist; and Roy P.E. Yanong, professor, Tropical Aquaculture Laboratory, School of Forest, Fisheries, and Geomatics Sciences, Program in Fisheries and Aquatic Sciences, UF/IFAS Extension, Gainesville, FL 32611.

Contacts

  • Deborah Pouder
  • Roy Yanong
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