Merck Manual

Please confirm that you are a health care professional

honeypot link
Fish Diseases of Regulatory Concern in the US

Fish Diseases of Regulatory Concern in the US


Causative Agent

Susceptible Species

Clinical Signs and Pathology

Temperature Range

Status in US

Viral hemorrhagic septicemia (Egtved disease)


Family: Rhabdoviridae

Primary: salmonids (Oncorhynchus spp), turbo, herring and spat (Clupea spp), Japanese flounder

Secondary: grayling, whitefish, pike, Atlantic and Pacific cod, haddock, and many freshwater, marine, and estuarine species

Acute form: nonspecific hemorrhaging (eyes, fins, or skin), darkening, exophthalmia, ascites

Chronic form: few signs

Neurologic form: spinning or flashing

Gross: enlarged spleen, ascites, necrotic kidney

Histologic: focal necrosis of kidney liver, spleen; hemorrhage in muscle

48°–54°F (9°–12°C) optimal

Present in wild populations, sporadic, limited distribution; endemic in Pacific Northwest and Alaska (wild salmonids, haddock, and cod); emerging disease in Great Lakes region in a wide variety of fishes.

Infectious hematopoietic necrosis


Family: Rhabdoviridae

Primary: cultured salmonids (Oncorhynchus spp); lake trout and char (Salvelinus spp) are resistant

Rapidly increasing mortality (fish < 1 year), lethargic but sporadic bursts of rapid swimming occur, protruding vent, fecal casts, exophthalmic, pale gills, darkening, abdominal distention or ascitic fluid (possibly bloody)

50°–54°F (10°–12°C) optimal; rare >15°C (59°F)

Present in western US, sporadic, limited distribution; endemic in Pacific Northwest and Alaska (wild salmonids); also present in parts of Europe and Asia

Spring viremia of carp


Family: Rhabdoviridae

Primary: carp (including koi, goldfish), sheatfish (European catfish), orfe, tench

Nonspecific: darkening, exophthalmic, pale gills, distended abdomen, ascites, hemorrhage (gills, skin, or eye), petechiae in organs (including swim bladder), protruding vent with thick mucoid fecal cast

Coinfection with Aeromonas or other bacteria common

54°–72°F (12°–22°C)

US is free (last occurred in captive fish in 2004, wild fish in 2007); occurs in eastern Europe, Russia, China, and Middle East

Epizootic hematopoietic necrosis


Family: Iridoviridae

Primary: redfin perch

Secondary: rainbow trout

(wild and farmed fish)

Acute and high mortality of redfin perch; darkening, ataxia, lethargy, hemorrhage around nares; morbidity and mortality of rainbow trout less severe; Histologic: necrosis, renal hematopoietic tissues

Redfin perch: 54°F (>12°C)

Rainbow trout: 52°–63°F (11°–17°C)

Experimental: 46°–70°F (8°–21°C)

Has never occurred in US; endemic in Australia

Endemic in Australia

Red sea bream iridoviral disease


Family: Iridoviridae

Red sea bream, many

other estuarine species, other marine species

Severe anemia, lethargic, pale gills, enlarged spleen

Has occurred in imported tropical marine fish in US; occurs in Japan and Taiwan

Infection with HPR-deleted or HPR0

Infectious salmon anemia


Family: Orthomyxoviridae

Atlantic salmon

Brown trout, sea trout, rainbow trout

Pale gills, severe anemia (PCV < 10%), swollen liver (black or brown color), ascites, petechiae of viscera, mesenteric fat, swim bladder

In vitro:

Maximum replication 59°F (15°C)

No replication 77°F (25°C)

Present in northeast US, sporadic, limited distribution; endemic in Maine, New Brunswick, Scotland, and Norway

Endemic in Maine, New Brunswick, Scotland, and Norway

Infection with salmonid alphavirus (pancreas disease or sleeping disease)


Family: Togaviridae

Atlantic salmon, rainbow trout, brown trout

Necrosis of exocrine pancreas, heart and skeletal muscle changes

54°–59°F (12°–15°C)

Has not occurred in US; detected in Ireland, UK, France, Germany, Italy, Spain, Switzerland, Poland, and Norway

Koi herpesvirus

Cyprinid herpesvirus-3

Family: Alloherpesviridae

Common carp and hybrids, including koi and ghost carp

Severe necrosis gill tissue

72°–78°F (22°–25.5°C) optimal*

Present in US, sporadic, widely distributed

Epizootic ulcerative syndrome (mycotic granulomatosis)

Aphanomyces invadans

Oomycetes (water mold)

Atlantic menhaden, striped mullet, many other freshwater and estuarine species; snakeheads, barbs (Puntias spp) sensitive; gouramis, goldfish and other ornamentals susceptible; tilapia resistant

Necrotizing deep ulcers (penetrate body wall), granulomatous tissue response; deep ulcers with red centers, white rims; invasive nonseptate hyphae (culture possible but difficult)

77°F (< 25°C)

(reduced salinity also contributes in brackish systems)

Present in US, sporadic, limited distribution; reported in North America, Africa, Asia, and Australia

Gyrodactylus (Gyrodactylus salaris only)


Gyrodactylus salaris only

Atlantic salmon, rainbow trout, brook trout, North American lake trout, brown trout, grayling arctic char

Has never occurred in US

*Mortalities stop at 86°F ( >30°C) , but survivors remain carriers.