Fish Pathology Archive
Fish Pathology Archive
This section was developed alongside the necropsy manual and designed to give an overview of some lesions attributed to both infectious and non-infectious diseases of the species covered. We have included external and internal images for reference, which are intended as a guide for the pathologist. Full descriptions and histological detail are available for salmonids, but examples from flatfish and gadoids are not widely available. We hope readers will benefit from having these images included as part of the necropsy manual. Please note that the images are subject to Crown Copyright and should not be copied from this web site.
External Disease Signs
Small furuncle and haemorrhagic ulcer attributed to Aeromonas salmonicida infection in Atlantic salmon (courtesy of FHI)
Numerous Argulus on ventral surface of freshwater fish (courtesy of FHI)
Focal extensive deep ulcer with healed margins attributed to infection by Flavobacterium sp. in rainbow trout (courtesy of FHI)
Exophthalmia and cornea opacity and ulceration in wrasse (courtesy of FHI)
Multiple circumscribed ulcerations on head and operculum attributed to oomycete infection of Atlantic salmon (courtesy of FHI)
Thin, potentially runt post smolts (courtesy of FHI)
Hyperpigmentation of blind side of common dab
Anophthalmia noted from Atlantic salmon
Multiple roundish blackened skin lesions consistent with Cryptocotyle lingua infection of whiting
Focal yellowish raised lesion ventral of lateral line consistent with early stage of red mark syndrome on rainbow trout
Shortened operculum due to damaged branchiostegal membrane in rainbow trout
Focal raised reddened lesion on flank attributed to Red mark syndrome in rainbow trout
Sharply demarcated lesions attributed to seal damage on Atlantic salmon
Lordosis in Atlantic salmon
Shortened operculum in rainbow trout
Perforated cornea and loss of lens together with hemorrhage in bulbus in rainbow trout
Circular ulceration on operculum and oomycete infection in rainbow trout, additionally note cataract and focal ulcerative lesion on flank
Extended hemorrhages on ventral body site together with severe sea lice infestation, note also eroded fins
Extended skin ulceration on caudal body part, multifocally deep ulcerations due to Tenacibaculum sp. infection
Clogging of gill filaments and whitish discoloration consistent with multiple necroses and epithelial hyperplasia with increased mucous production in Atlantic salmon (courtesy of FHI)
Diffuse proliferative gill lesion attributed to X-cell lesion in common dab
Abnormal pigmentation on ocular side of common dab
Abnormal pigmentation on blind side of common dab
Focal ulcer with evidence of healing near ventral fin of common dab
Spinal deformity in cudal body part of haddock
Skin, focal raised whitish nodule with irregular surface, consistent with papilloma on operculum of common dab
Multiple whitish raised pleiomorphic lesions, sometimes ulcerated, consistent with multiple papillomas on common dab
Multiple raised granular lesions on blind site consistent with lymphocystis infection in common dab
Close up of hyperpigmentation on blind side of common dab
Close up of hyperpigmentation of common dab
Club-like, distal, proliferative gill lesions of unknown origin in flat fish
Yellow faecal casts from Atlantic salmon
Healed sharply demarcated linear lesion attributed to mechanical damage on Atlantic salmon (courtesy of FHI)
Exophthalmia and diffuse haemorrhage on ventral surface of Atlantic salmon (courtesy of FHI)
Dorsal head and opercula, irregulr circular ulcerations attributed to oomycete infection in Atlantic salmon (courtesy of FHI)
Abdominal distention and reddened area on lateral line of rainbow trout.
Extended, raised, irregular and haemorrhagic lesion on body site and multiple petechia on belly of rainbow trout (courtesy of FHI)
Multiple raised reddened skin lesions attributed to red mark syndrome from rainbow trout, note also multiple small hemorrahgic lesions and small ulcers, also exophthalmia (courtesy of FHI)
Focal extensive deep ulcer with defined margins attributed to Vibrio infection on flank of Atlantic salmon (courtesy of FHI)
Thin, potentially runt post smolts
Multiple raised skin lesions. Note superficial ulceration and scale loss, consistent with liquefactive necrosis of dermis and musculature due to Aeromonas salmonicida infection in rainbow trout.
Focal prolferative lesion on head region consistent with Dermocystidium sp. infection in carp.
Multiple whitish nodular lesions diffusely distributed over whole body consistent with Ichthyophthirius multifiliis infection in rainbow trout.
Multiple whitish irregular shaped slightly raised areas randomly distributed over whole body, consistent with epithelial hyperplasia due to Cyprinid Herpesvirus 1 infection.
Rounded, yellowish tumorous overgrowth in gill’s filaments consistent with a hamartoma, in an otherwise healthy A.salmon (courtesy of M. Yousaf- Norwegian Vet. Institute).
Internal Disease Signs
Pectinate haemorrhage on liver and perivisceral fat attributed to enteric redmouth in rainbow trout
Enlarged kidney and spleen (splenomegaly) with multiple granulomas consistant with bacterial kidney disease, note yellowish faecal casts in intestine
Multiple haemorrhages in liver and ulcerations on skin attributed to Vibrio sp. infection in Atlantic salmon
Petechiae on liver with generalised anaemia in rainbow trout caused by a bacterial septicaemia
Multiple whitish polymorphic nodules consistent with granulomas and single Anisakis on liver of flatfish
Multiple Anisakis on liver of common dab
Multiple Anisakis on liver of Atlantic cod
Vertebral fusion of about 9 vertebae in haddock
Liver, petechial haemorrhages and skin ulcerations attributed to Vibrio infection in Atlantic salmon
Liver with multiple whitish, sligthly raised and circular lesions with reddish center consistent with granulomatous hepatitis attributed to Piscirickettsia salmonis in Atlantic salmon
Chart used to categorise liver colour, eg for diagnostics of ISA (courtesy of FHI)
Diffusely distributed petechial haemorrhage in musculature and perivisceral fat attributed to viral haemorrhagic septicaemia in rainbow trout
Mottled liver appearance and multiple Anisakis on liver of wild Atlantic cod (courtesy of FHI)
Multiple fluid filled cycts of irregular size in liver, consistent with Polycystic liver from Atlantic salmon (courtesy of FHI)
Petechiae on liver with generalised anaemia in rainbow trout
Pectinate haemorrhage on liver and perivisceral fat attributed to enteric redmouth in rainbow trout
Enlarged kidney and spleen (splenomegaly) with multiple granulomas consistant with bacterial kidney disease, note yellowish faecal casts in intestine
Widespread petechial haemorrhage in muscle and perivisceral fat tissue attributed to viral haemorrhagic septicaemia virus in Atlantic salmon
Multiple granuloma (whitish proliferative lesions) in kidney attributed to Exophiala infection in Atlantic salmon
Multiple whitish noluar lesions (granuloma) in kidney, spleen and intestine and splenomegaly in Atlantic cod attributed to infection by Francisella philomiragia subsp. noatunensis
Variable sized whitish nodules (granuloma) in liver attributed to Mycobacterium infection in Atlantic salmon
Kidney, swollen, proliferative lesion mainly affecting the caudal part of the kidney with multiple whitish nodules consistent with granulomatous nephritis attributed to Exophiala infection
Granuolomatous lesions in kidney, liver and spleen attributable to bacterial kidney disease in Atlantic salmon
Multiple greyish pleiomorphic nodules in liver and peritoneum, possible consistent with neoplastic or granulomatous lesion from rainbow trout
Multiple whitish, sligthly raised areas with reddish center on liver consistent with granulomatous hepatitis attributed to Piscirickettsia salmonis in Atlantic salmon
Pale organs, lack of body fat attributed to infection by infectious pancreatic necrosis virus in Atlantic salmon
Kidney, multiple whitish nodules, sometimes interconnected forming strand like lesions attributed to nephrocalcinosis in rainbow trout
Eubothrium infestation in Atlantic salmon
Diffuse haemorrhage in spleen and kidney and splenomegaly attributed to infection by infectious salmon anaemia virus
Dark liver due to congestion and diffuse haemorrhage attributed to infection by infectious salmon anaemia virus
Cystidicola farionis (multiple nematodes) infestation in swim bladder of rainbow trout
Splenomegaly and blurred spleen margins due to Flavobacterium psychrophilum infection in rainbow trout fry (RTFS= rainbow trout fry syndrome).
