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The Atlantic wolffish (AW) and the spotted wolffish (SW) are long-lived fish found in the North Atlantic and Arctic oceans and are respectively classified as special concern and threatened species, mainly due to fisheries bycatch. To better understand health issues associated with the care of these species in public aquaria, reports from all necropsies performed in 2 zoological institutions between 2009 and 2019 were reviewed (31 AW and 8 SW). These wolffish were fed with a similar fish-based diet and kept in multi-species exhibits with comparable environmental parameters. The most frequent necropsy findings were the presence of xanthomas (AW: 41.9%; SW: 75.0%), nephrocalcinosis (AW: 42.9%; SW: 75.0%) and urocystoliths (AW: 6.5%; SW: 62.5%). Xanthomas were mostly located at the base of pectoral fins and were characterized by extensive granulomatous inflammation centered on accumulations of partly mineralized degenerate fatty material, mainly composed of cholesterol crystals. Nephrocalcinosis was characterized by the deposition of calcium salts within the renal tubules and was commonly associated with tubular necrosis. The aquarium-housed wolffish were fed a coldwater fish-based diet. However, the natural diet of wolffish is composed mostly of invertebrates such as urchins and crustaceans. Differences in nutrient composition between these diets, such as lipid and mineral content, may have contributed to the development of xanthomatosis, nephrocalcinosis and urocystolithiasis in wolffish housed in these institutions.

The spotted wolffish Anarhichas minor is a promising new species for cold-water aquaculture. The broad host-range of piscine nodavirus (NV) and infectious pancreatic necrosis virus (IPNV) makes them potentially pathogenic to new fish species in aquaculture. IPNV and NV strains highly pathogenic in farmed Atlantic salmon Salmo salar and halibut Hippoglossus hippoglassus, respectively, in Norway were used for the challenge of spotted wolffish. In general, water-borne infection with IPNV and NV resulted in significant mortality among juveniles

Atypical strains of Aeromonas salmonicida are the causal agent of atypical furunculosis or ulcer disease in various fish species, including spotted wolffish Anarhichas minor, which is a promising species in the Norwegian fish-farming industry. Isolates of atypical A. salmonicida comprise a very heterogenous group showing large variety in biochemical, molecular and virulence characteristics. The genetic variability among atypical isolates from wolffish was characterised using amplified fragment length polymorphism analysis: AFLP-fingerprinting. Additional isolates from halibut Hippoglossus hippoglossus, turbot Scophthalmus maximus, cod Gadus morhua and several salmonid fishes were included for assessment of variability and relatedness among a total of 56 atypical isolates of A. salmonicida. They were compared to reference strains of A. salmonicida subspecies and to other Aeromonas species pathogenic in fishes. AFLP-fingerprints subjected to similarity analysis yielded a grouping of the isolates into several clusters, revealing genetic heterogeneity among the isolates. There seems to be a correlation between genetic similarity among isolates and the fish host. The Icelandic isolates, mainly from cod, formed a very homogeneous subcluster, which was closely related to the wolffish isolates. All atypical isolates from spotted and common wolffish grouped together in a large cluster and appear to be very homogeneous, even though they had been isolated over a period of 8 yr at different locations in Norway. On the other hand, most of the isolates from turbot and halibut grouped together into 2 different clusters, while the 9 atypical isolates from salmonids appeared in 4 different clusters. Thus, the atypical isolates of A. salmonicida from halibut, turbot and salmonid fishes seem to be more genetically diverse than those from wolffish and cod.

Spotted wolffish Anarhichas minor (approx. 0.7 g) were found to be susceptible to infection with a nodavirus isolated from Atlantic halibut (AHNV) by bath-challenge. During the acute stage of infection, 4 to 8 wk post-challenge, viral encephalopathy and retinopathy (VER) were diagnosed by histopathology, immunohistochemistry (IHC) and reverse transcriptase-polymerase chain reaction (RT-PCR). Accumulated mortality was 52% in the challenged group. The surviving fish were sampled 16 wk post-challenge, by which time they had grown to approximately 17 g. No clinical signs of VER were observed in these fish. RT-PCR examination revealed the presence of nodavirus in several organs of the survivors, but no immunopositive cells were detected by IHC. Nodavirus was reisolated from fish at the last sampling in SSN-1 cells, showing that nodavirus retains virulence in persistently infected wolffish for at least 16 wk post-bath-challenge.

Atypical Aeromonas salmonicida strains comprise a heterogeneous group in terms of molecular and phenotypic characteristics. They cause various conditions of ulcer diseases or atypical furunculosis and are being isolated in increasing number from various fish species and geographical areas. Several marine fish species susceptible to atypical A. salmonicida, including spotted wolffish Anarhichas minor O., are now being farmed and new vaccines may be needed. A commercial furun- culosis vaccine for salmon is reported to protect wolffish poorly against experimental challenge with atypical A. salmonicida. The protective antigen(s) in furunculosis vaccines is still unclear, but in oil- adjuvanted vaccine for Atlantic salmon Salmo salar L., the surface A-layer was shown to be important for protection. In spotted wolffish, the efficacy of atypical furunculosis vaccines seems to vary with the atypical A. salmonicida strains used as bacterin in the vaccine. In the present study we investi- gated whether differences in the A-layer protein among atypical strains might be responsible for the observed variation in vaccine efficacy. Atypical A. salmonicida strains from 16 fish species in 11 coun- tries were compared by genome polymorphism analysis using amplified fragment length polymor- phism (AFLP) fingerprinting and by comparative sequencing of the vapA genes encoding the A-pro- tein. The A-protein sequences appeared to be highly conserved except for a variable region between Residues 90 to 170. Surprisingly, the grouping of strains based on AFLP- or A-protein sequence sim- ilarities was consistent. In addition, serological differences in the A-protein among the strains were demonstrated by an A-protein-specific monoclonal antibody. Vaccines based on atypical A. salmoni- cida strains possessing genetically and serologically different A-layer proteins were shown to result in significantly different protection in spotted wolffish.