Merck Manual

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Common Metazoan Parasites of Fishes

Common Metazoan Parasites of Fishes

Parasites

Tissue

Susceptible Species

Signs

Diagnosis

Treatment

Myxozoans (IH)

Myxosoma cerebralis (whirling disease)

Head, cartilage, backbone

Rainbow trout, salmonids

Blacktail, skeletal deformity

Histology, isolation of parasite

None; regulatory concern

Ceratomyxa shasta

Posterior intestine

Salmonids (Pacific NW)

Weight loss, distended and hemorrhagic vent

Wet mount, histology

None; regulatory concern

Aurantiactinomyxon ictaluri (PGD, HGD)

Gill

Channel catfish

Mortality, piping

Wet mount, histology

None

Henneguya

Gill

Channel catfish, other

None, severe hypoxia

Wet mount

None

Sphaerospora auratus (renal dropsy)

Kidney

Goldfish (pond-reared)

Mortality, severely enlarged and cystic kidney

Histology

None

Tetracapsuloides bryosalmonae (proliferative kidney disease)

Kidney

Rainbow trout, all salmonids

Lethargy, darkening, fluid accumulation, exophthalmia

Wet mount, histology

None

Monogeneans

Gyrodactylus (live bearer, except in Loricaridae)

Skin, fins

Goldfish, koi (predisposed)

Excess mucus, flashing, weight loss

Wet mount

Praziquantel in nonfood fishes, formalin

Family: Ancyrocephalidae

Family: Dactylogyridae (egg layers)

Gills

Goldfish, koi, angelfish, discus, channel catfish

Piping, coughing, weight loss, skin lesions

Wet mount

Praziquantel in nonfood fishes, formalin

Capsalids; Benedenia, Neobenedenia (egg layer)

Epithelium of skin and gills

Marine tropicals, other marine species, marine angelfish

Epithelial lesions, flashing, weight loss, mortality

Visual exam, wet mount

Praziquantel in nonfood fishes, formalin

Polyopisthocotylea

Gill

Striped bass, hybrid striped bass, Florida pompano

Pale gills, piping, mortality

Visual exam, wet mount

Praziquantel in nonfood fishes, formalin

Trematodes (IH usually mollusc)

Heterophyidae

Gill

Redtail shark, black shark, rainbow shark, angelfish (FW), other pond-reared fish, aquarium fish

Flared gills, hypoxia, piping, do not tolerate shipping and handling

Wet mount

Clinostomum

Skeletal muscle

Largemouth bass, centrarchids, hybrid striped bass

Yellow grub

Direct visualization, wet mount

Bolbophorus confusus

Skeletal muscle, viscera

Channel catfish

None

Direct visualization, wet mount

Posthodiplostomum

Viscera, heart, posterior kidney

Largemouth bass, bluegill, centrachids, salmonids, other fish

None

Direct visualization, wet mount

None

Diplostomum

Eye (lens)

Fish are IH (unspecified species)

Cataracts, blindness

Direct visualization, histology

None

Cestodes

Diphyllobothrium latum

Viscera, musculature

Salmonids, other FW species

Adhesions, sterility (if gonads affected)

Direct visualization, wet mount

Praziquantel in nonfood fishes

Corallobothrium

Intestine (adult)

Channel catfish

None

Direct visualization, wet mount

Praziquantel in nonfood fishes

Proteocephalus ambloplitis

Ovary (larval stage)

Largemouth bass

Sterility

Direct visualization, wet mount

Praziquantel in nonfood fishes

Bothriocephalus acheilognathi

Intestine (adult)

Carp, aquarium fish

Weight loss, enteritis, mortality

Direct visualization

Praziquantel in nonfood fishes

Acantho-cephalids

Acanthocephalus

Intestine

Wild-caught freshwater fishes, wild-caught marine fish

Enteritis, mortality

Direct visualization

Nematodes (fish as DH)

Capillaria

Intestine

Angelfish, discus, other aquarium fish

Weight loss, pot belly

Direct visualization, wet mount

Fenbendazole, levamisole

Camillanus

Posterior intestine

Largemouth bass, other centrarchids

Visualize worms protruding from anus

Direct visualization

Fenbendazole, levamisole

Philometra

Posterior intestine

Aquarium fish

Visualize worms protruding from anus

Direct visualization

Fenbendazole, levamisole

Nematodes (fish as IH)

Eustrongylides

Encysted in coelom

Angelfish, other aquarium species

Weight loss, pot belly

Direct visualization

Contracaecum

Encysted in viscera

Largemouth bass, centrarchids

Often none

Direct visualization

Leeches

Leech

Skin

FW game fish, aquarium fish

Anemia, weight loss

Direct visualization

None

Note: FW = freshwater; IH = intermediate host; DH = direct host; KMnO4 = potassium permanganate