Sea Bass

Diseases and Conditions

• In sea bass production today, vibriosis caused by Vibrio anguillarum serotype O1 is a limiting factor for further growth of the industry (Haenen et al., 2014). Vibriosis outbreaks occur both in hatchery and on-growing stages of production and are usually related to stressful situations and rapid temperature fluctuations and the disease is characterized by the presence of hemorrhages in skin and the base of fin in larger fish and necrosis of the trunk of the tale in juveniles. The pathogen causes a haemorrhagic septicaemia. Mortality varies from 1% (large fish) - 30% (medium size fish) without treatment.

• Pasteurellosis causes a septicemia which may have an acute, sub-acute to chronic course; the acute form is generally observed in small or juvenile fish and can induce high mortality (up to 90-100%) with few other signs of disease than darkening of the skin and/or slight haemorrhagic areas in the head and gills and enlargement of the spleen. The chronic form occurs in larger fish and is characterized by the presence of white nodules in the internal organs, especially spleen and kidney.

Rapid diagnosis of disease outbreaks is essential for proper handling and control.  The diagnosis may be performed by pathological findings and bacteriological examinations. PCR is a good alternative for verification of the presence of pathogen because the method is very sensitive and quick to perform. Serological methods, as agglutination test, may also be used for pasteurellosis diagnosis.

The administration of both immersion and injection vaccination as preventive measures are the optimal options to control the disease in juveniles and larger fish at the sea.