Syncytial Hepatitis of Tilapia – Histopathology

Gastrointestinal Tract, Liver
by Hugh Ferguson
Liver; O. niloticus L.; dissociation of hepatocytes containing brown-staining lipoprotein, degeneration and single cell necrosis, plus early hepatocellular syncytial cell formation and moderate diffuse inflammation H&E.

Syncytial Hepatitis of Tilapia (SHT) is a newly described viral disease reported from Ecuador, Israel, Colombia and several other countries where tilapia farming is present. The most consistently described target organs are the liver and gastrointestinal tract, although there are some reports of lesions within the central nervous system. The presence of a novel virus with close affinity to the family Orthomyxoviridae has been demonstrated within hepatocytes of affected fish. Histopathological lesions include necrotizing hepatitis with distinctive hepatocellular syncytial giant cell formation, dissociation of hepatocytes...

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Haemorrhagic Smolt Syndrome (HSS) – Gross Pathology

Multisystem
by Carlos Sandoval
Atlantic salmon, with visceral fat haemorrhage and pale liver.

HSS is a condition of unknown aetiology, which affects Salmo salar leading to dramatic pathological changes. The disease occurs in pre smolts, smolts and post smolts. Affected fish typically have good body condition, without obvious weight loss; they show lethargy, superficial swimming and dark colouration. Bilateral exophthalmia and increased respiratory rate can sometimes be observed The external gross findings include pale gills, with haemorrhages in the branchial arches and lamellae, plus petechiae and ecchymoses ventrally and at the base of the fins. Internally, generalized visceral...

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Muscular Melanosis – Gross Pathology

Musculoskeletal System
by Carlos Sandoval
Muscular melanosis.

The term melanosis is used to describe the presence of unusual amounts of melanin in abnormal areas. Melanin is considered to plays a defensive role, since it is capable of absorbing and neutralizing free radicals, cations and potentially toxic compounds derived from the breakdown and phagocytosis of cellular material. Inflammatory reactions and tissue degeneration in bony fish frequently involve melanomacrophages. These macrophages contain fragments derived from phagocytized debris and cells, often erythrocytes, and pigments such as melanin, lipofuscin and haemosiderin. In salmonids these cytoplasmic granules...

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Proliferative Gill Disease (PGD) – Gross Pathology

Gills and Pseudobranchs
by Carlos Sandoval
PGD in Atlantic salmon showing white spots (clubbing), distal third of filaments.

PGD is a multifactorial worldwide disease with both infectious and non-infectious causes.  PGD leads to significant problems in Atlantic salmon (Salmo salar) and many other species. Among the infectious causes are viruses (Atlantic salmon paramyxovirus-ASPV, Salmon gill poxvirus-SGPV), bacteria (Tenacibaculum maritimus, Piscichlamydia salmones, Candidatus Clavochlamydia salmonis), parasites (Neoparamoeba perurans, Loma salmonae, Ichthyobodo spp., Trichodina sp.). Non-infectious causes include phytoplankton and zooplankton. Gross pathological changes include “clubbing”, in which thickened white areas of hyperplastic epithelium can be easily seen, mainly at the ends or distal third...

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Pseudochattonella cf. verruculosa – Phytoflagellate

Gills and Pseudobranchs
by Carlos Sandoval
Pseudochattonella cf. verruculosa - Phytoflagellate

Pseudochattonella cf. verruculosa is a phytoflagellate, Dictyochophyceae class that has abundant golden chloroplasts. It has two flagella, one of which, is directed forward, thereby allowing cell movement. The cell size varies between 12 – 45 microns depending on the stage of its life cycle. Its surface, the cell is covered by specialized structures that resemble papillae or warts, hence the name “verrucous”. These structures are mucocysts through which mucus is discharged. It is distributed in water bodies that fluctuate between 10 – 18 oC, salinities...

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