inability to evacuate gas via the pneumatic duct. Affected
fish have increased buoyancy and an altered centre of gravity
causing them to swim erratically with the tail up, on their
sides, or with their belly up. Fish with moderate over-inflated
swim bladder may live for a long period, while severely
affected fish can show a visibly enlarged abdomen and
spend a lot of energy to stay in position, and may die from
exhaustion. Affected fish are also more vulnerable to
predators. At necropsy, the swim bladder is grossly overinflated and may more or less displace other organs in the
abdominal cavity. General stress or stress associated to inadequate water depth, is believed to be important for the
development of this condition. Diagnosis is made from clinical observations and an enlarged swim bladder.
Fig. 11.14 Ascites and haemorrhage in the posterior intestine in
farmed Atlantic salmon smolt with haemorrhagic smolt syndrome
Fig. 11.13 Farmed Atlantic salmon smolts with haemorrhagic smolt syndrome. Haemorrhage in white muscle and internal organs
Fig. 11.15 Haemorrhage in the area between red and white muscle in
farmed Atlantic salmon smolt with haemorrhagic smolt syndrome
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11 Idiopathic Diseases