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In this study experimental challenges with Moritella viscosa, the causative agent of winter ulcers in salmonids, were performed on juvenile Atlantic cod and Atlantic halibut. The challenges involved both intramuscular (i.m.) and intraperitoneal (i.p.) injections and bath with a strain originally isolated from Atlantic salmon. Cod was found to be significantly more sensitive than halibut to the infection. Both fish species were found to be more sensitive to i.m. than i.p. challenges. Both challenges induced a systemic disease in cod and halibut, but only cod was infected with an experimental bath challenge. Pathognomonic signs were found to be comparable with those described in M. viscosa-infected salmon and turbot. The main distinguishing pathological sign was that the cod showed host response to M. viscosa infection resulting in granuloma formation in infected tissues, which is a known response of cod to a infection with another Gram-negative bacterium, Aeromonas salmonicida. Re-isolation of M. viscosa from kidneys of cod and halibut with clear disease signs was problematic and optimization of isolation measures is needed. The results of this study indicate that M. viscosa infection may be a risk factor in cod farming, but that halibut is more resistant. [ABSTRACT FROM AUTHOR]

Turbot was shown to be sensitive to injection challenges byAeromonas salmonicidasubsp.achromogenes(Asa). A systemic disease was induced and the bacterium was isolated from various internal organs. Histopathological changes involved haemorrhages, necrosis and degeneration in skin and muscle, haemorrhages and necrosis in kidney, degeneration in the heart muscle, and fusion of the secondary gill lamellae. A polyvalent commercial salmon vaccine, containingA. salmonicidasubsp.salmonicidaas one of five antigens, did not confer protection in turbot against an experimental Asa infection 13 weeks post-vaccination. Vaccination induced a significant antibody response against Asa cells but not against extracellular products of the bacterium. The results of the study indicate that Asa may be a potential threat to turbot farming and that the development of new turbot vaccines is needed. [ABSTRACT FROM AUTHOR]

Moritella viscosais the causative agent of winter ulcers in farmed salmonids and Atlantic cod in countries around the North Atlantic. The bacterium has also been isolated from various marine fish species. Bacterial diseases have been a limiting factor in farming of turbot, butM. viscosahas not so far been isolated. In this study, turbot was shown to be sensitive toM. viscosainfection in experimental challenges. Pathological changes in infected turbot were comparable with those previously described for winter ulcers in salmon. A multivalent commercial salmon vaccine, containingM. viscosaas one of five antigens and a mineral oil adjuvant, did not protect turbot against challenge 13 weeks post-vaccination. Weight gain of vaccinated turbot compared with controls was not reduced 7 weeks post-vaccination. Vaccination did not induce a specific anti-M. viscosaresponse, while elevated anti-M. viscosaantibody levels were detected both in vaccinated and unvaccinated fish 5 weeks post-challenge. The vaccine did, however, induce an antibody response againstAeromonas salmonicida, another vaccine component. Minor intra-abdominal adhesions were detected in vaccinated fish and fish injected with a mineral oil adjuvant. The measurement of various innate humoral immune parameters did not reveal significant differences between vaccinated and control groups. [ABSTRACT FROM AUTHOR]