Blue sac disease (BSD) – Gross Pathology

Blue sac disease in Atlantic salmon yolk-sac fry. Note a gill haemorrhage.

Blue-sac disease (BSD) or dropsy (hydrocoele embryonalis) is an abnormal condition that affects the egg and sac fry stages, typically of trout and salmon, but also of other freshwater fishes whose young emerge with a relatively large yolk sac.  It is characterized by abnormal accumulation of fluid with bluish tint between the yolk-sac and the outer membranes of the fry. It may also involve the pericardium and lymphatic spaces. BSD can be observed shortly after hatching and become more apparent within a few days. Blue-sac...

Nephrocalcinosis in Fish – Gross pathology

Figure 1. Gross appearance of nephrocalcinosis. The kidney is swollen and grey with an irregular surface and white mineral deposits in the ureters.

Nephrocalcinosis (or urolithiasis) in fish is a chronic inflammatory condition of unknown aetiology in which calcium and other minerals precipitate as hydroxyapatite within the distal renal tubules and collecting ducts. The disease usually records low mortality and although food conversion efficiency is probably impaired, the major concern about the condition centres round a reduction in carcase quality at slaughter. In severe cases, the muscle dorsal to the kidney may also be affected. There are some predisposing factors for this condition like high levels of carbon...

Cardiomyopathy syndrome in Atlantic salmon (CMS) – Histopathology

CMS in ventricle of Atlantic salmon showing severe myocarditis of spongy layer. Note that the compact layer (on the left) is largely unaffected.

Cardiomyopathy syndrome (CMS) is a severe cardiac disease affecting Atlantic salmon characterized by prolonged periods of usually low-level mortalities. The disease was first recognized in farmed Atlantic salmon in Norway in 1985 and subsequently in farmed salmon in the Faroe Islands, Scotland and Ireland. CMS is a transmissible disease that has been causally linked to the Piscine Myocarditis Virus (PMCV), closely allied to the Totiviridae. CMS usually causes mortality in adult or maturing fish after 12 to 18 months in seawater, resulting in substantial economic...

SPINAL FRACTURE DUE TO ELECTRIC SHOCK

Atlantic salmon, presmolt, FW, exposed to electric shock. Note the spinal fracture associated haemorrhage. The cause of the electric shock was an energized cable that fell into the tank.

Bone is a highly anisotropic, viscoelastic material that has the ability to continually adapt to changes in its physiological or mechanical environment. The capacity of bone to resist mechanical forces and fractures depends not only on the quantity of bone tissue but also on its quality. Bone is a composite material, made from a collagenous matrix and from minerals. The collagenous matrix provides toughness (fracture resistance) and the minerals increase the bone’s stiffness (bending resistance). By itself, the mineral phase is brittle and fractures easily....

Bacterial gill disease – Gross Pathology

This rainbow trout fingerling with BGD shows the typical flared opercula of respiratory distress. Note that the edge of the flared operculum is eroded. This erosion is typical of intensively-reared fish; its cause is unknown, but might be the result of higher-than-optimal bacterial enzymes in and around the branchial cavity. Whatever the cause, the consequence is a huge reduction in the ability of the animal to pump water due to elimination of the water-tight seal between the trailing edge of the operculum and the body of the fish (the cleithrum). Thus the negative pressure of the opercular pump is greatly reduced. And this in an animal that is trying to pump larger-than-normal volumes of water over its gills due to the hypoxaemia of BGD!

Bacterial gill disease (BGD) occurs in several species, but it is an especially serious problem of intensive salmonid culture, and in some parts of the world it is the most common disease, especially in fry and fingerlings. BGD is characterized by explosive morbidity and mortality rates, attributable to bacterial colonization of gill surfaces. Despite such pronounced clinical signs and high mortality, pathological changes are surprisingly few and hard to find in the acute disease. It is only when (if) the fish survive for a few...

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