Merck Manual

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Fish Diseases of Regulatory Concern in the USA

Fish Diseases of Regulatory Concern in the USA

Disease

Causative Agent

Susceptible Species

Clinical Signs and Pathology

Temperature Range

Status in USA

Viral hemorrhagic septicemia (Egtved disease)

Novirhabdovirus

Family: Rhabdoviridae

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

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

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

Chronic form: few signs

Neurologic form: spinning/flashing

Gross: enlarged spleen, ascites, necrotic kidney

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

9°–12°C (48°–54°F) 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

Infectious hematopoietic necrosis

Novirhabdovirus

Family: Rhabdoviridae

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

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

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

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

Spring viremia of carp

Vesiculovirus

Family: Rhabdoviridae

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

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

Coinfection with Aeromonas or other bacteria common

12°–22°C (54°–72°F)

USA 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

Ranavirus

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: >12°C (54°F)

Rainbow trout: 11°–17°C (52°–63°F)

Experimental: 8°–21°C (46°–70°F)

Has never occurred in USA; endemic in Australia

Endemic in Australia

Red sea bream iridoviral disease

Megalocytivirus

Family: Iridoviridae

Red sea bream, many

other estuarine species, other marine species

Severe anemia, lethargic, pale gills, enlarged spleen

Has never occurred in USA; occurs in Japan and Taiwan

Infection with HPR-deleted or HPR0

Infectious salmon anemia

Isavirus

Family: Orthomyxoviridae

Atlantic salmon

Brown trout, sea trout, rainbow trout

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

In vitro:

Maximum replication 15°C (59°F)

No replication 25°C (77°F)

Present in northeast USA, 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)

Alphavirus

Family: Togaviridae

Atlantic salmon, rainbow trout, brown trout

Necrosis of exocrine pancreas, heart and skeletal muscle changes

12°–15°C (54°–59°F)

Has not occurred in USA; 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

22°–25.5°C (72°–78°F) optimala

Present in USA, 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)

<25°C (77°F)

(reduced salinity also contributes in brackish systems)

Present in USA, sporadic, limited distribution

Gyrodactylus (Gyrodactylus salaris only)

Monogenea

Gyrodactylus salaris only

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

Has never occurred in USA

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