Vertebral column deformity with curved cross-stitch vertebrae in Norwegian seawater-farmed Atlantic salmon, Salmo salar L.

Pathological changes in the vertebral column of farmed Atlantic salmon in Norway have been reported since the 1990s. Based on the characteristic radiographic findings, we here present a vertebral column deformity named "curved cross-stitch vertebrae" that mainly affects the middle aspect of the vertebral column. Sixty fish, from the west/northwest coast of mid-Norway, were sampled at slaughter and examined by radiography, computed tomography (CT), necropsy, macrophotography, and histology. The vertebral deformities were radiographically graded as mild, moderate, or marked. The main differences between these grades of changes were defined by increased curving of the peripheries of endplates, reduced intervertebral spaces, and vertical displacement of the vertebrae. The curved rims of endplates were located peripheral to a continuous and approximately circular borderline. The CT studies revealed small, multifocal, hypo-attenuating, round to crescent-shaped areas in the notochord, compatible with the presence of gas. Additionally, histology revealed that the axial parts of endplates had circular zones with perforations, through which either notochordal tissue prolapsed into the vertebrae or vascularized fibrochondroid proliferations extended from the vertebrae into the notochord. Inflammation was present in many vertebral bodies. To the best of our knowledge, this is the first report of gas in the notochord of fish.

Surveillance of the Sensitivity towards Antiparasitic Bath-Treatments in the Salmon Louse (Lepeophtheirus salmonis).

The evolution of drug resistant parasitic sea lice is of major concern to the salmon farming industry worldwide and challenges sustainable growth of this enterprise. To assess current status and development of L. salmonis sensitivity towards different pesticides used for parasite control in Norwegian salmon farming, a national surveillance programme was implemented in 2013. The programme aims to summarize data on the use of different pesticides applied to control L. salmonis and to test L. salmonis sensitivity to different pesticides in farms along the Norwegian coast. Here we analyse two years of test-data from biological assays designed to detect sensitivity-levels towards the pesticides azamethiphos and deltamethrin, both among the most common pesticides used in bath-treatments of farmed salmon in Norway in later years. The focus of the analysis is on how different variables predict the binomial outcome of the bioassay tests, being whether L. salmonis are immobilized/die or survive pesticide exposure. We found that local kernel densities of bath treatments, along with a spatial geographic index of test-farm locations, were significant predictors of the binomial outcome of the tests. Furthermore, the probability of L. salmonis being immobilized/dead after test-exposure was reduced by odds-ratios of 0.60 (95% CI: 0.42-0.86) for 2014 compared to 2013 and 0.39 (95% CI: 0.36-0.42) for low concentration compared to high concentration exposure. There were also significant but more marginal effects of parasite gender and developmental stage, and a relatively large random effect of test-farm. We conclude that the present data support an association between local intensities of bath treatments along the coast and the outcome of bioassay tests where salmon lice are exposed to azamethiphos or deltamethrin. Furthermore, there is a predictable structure of L. salmonis phenotypes along the coast in the data, characterized by high susceptibility to pesticides in the far north and far south, but low susceptibility in mid Norway. The study emphasizes the need to address local susceptibility to pesticides and the need for restrictive use of pesticides to preserve treatment efficacy.

Large scale modelling of salmon lice (Lepeophtheirus salmonis) infection pressure based on lice monitoring data from Norwegian salmonid farms.

Infection by parasitic sea lice is a substantial problem in industrial scale salmon farming. To control the problem, Norwegian salmonid farms are not permitted to exceed a threshold level of infection on their fish, and farms are required to monitor and report lice levels on a weekly basis to ensure compliance with the regulation. In the present study, we combine the monitoring data with a deterministic model for salmon lice population dynamics to estimate farm production of infectious lice stages. Furthermore, we use an empirical estimate of the relative risk of salmon lice transmission between farms, that depend on inter-farm distances, to estimate the external infection pressure at a farm site, i.e. the infection pressure from infective salmon lice of neighbouring farm origin. Finally, we test whether our estimates of infection pressure from neighbouring farms as well as internal within farm infection pressure, predicts subsequent development of infection in cohorts of farmed salmonids in their initial phase of marine production. We find that estimated external infection pressure is a main predictor of salmon lice population dynamics in newly stocked cohorts of salmonids. Our results emphasize the importance of keeping the production of infectious lice stages at low levels within local networks of salmon farms. Our model can easily be implemented for real time estimation of infection pressure at the national scale, utilizing the masses of data generated through the compulsory lice monitoring in salmon farms. The implementation of such a system should give the salmon industry greater predictability with respect to salmon lice infection levels, and aid the decision making process when the development of new farm sites are planned.

Vaccination and immune responses against atypical Aeromonas salmonicida in spotted wolffish (Anarhichas minor Olafsen) juveniles.

To study the effect of early vaccination, wolffish juveniles of size 50 and 90 mm, respectively, were vaccinated with an oil-adjuvanted atypical A. salmonicida bacterin. Vaccination resulted in significant protection after challenge with the homologous bacterial strain and specific antibody responses were demonstrated against whole bacteria as well as purified A-layer protein and LPS by ELISA and Western blotting but individual variation in immune responses was apparent. The A-protein was the most immunogenic bacterial component. In addition, higher numbers of immunoglobulin producing cells were detected by in situ hybridisation in kidney and spleen of vaccinated fish compared to non-vaccinated fish. Plasma cells were also present in gut and gills in equal numbers irrespective of treatment. No plasma cells were found in the skin. Finally, the frequencies of expressed V(H)families and C(L)isotypes of wolffish immunoglobulins were shown by PCR. The relative expression of the three variable regions of the Ig heavy chain and the three isotypes of the Ig light chain in the spotted wolffish spleen seemed to be unaffected by immunisation with a complex antigen like the A. salmonicida bacterin.

Immunoglobulin V(H)families and light chain isotypes in the spotted wolffish (Anarhichas minor Olafsen).

The spotted wolffish (Anarhichas minor Olafsen) is a species of the Perciformes, the most diverse and numerous order of all fish. A cDNA library from head kidney tissue was screened for immunoglobulin (Ig) heavy and light chain transcripts, and showed highest identity to Ig sequences from other perciform species. So far only one Ig class is described in spotted wolffish, but three V(H)families were identified among the heavy chain transcripts. Highest diversity was located at the CDR3 region and demonstrates the importance of this gene element to the antibody repertoire. Two V(L)families were identified among the light chain clones and three distinct isotypes were present. Use of polymerase chain reaction and in situ hybridisation techniques revealed individual variations in the relative expression of the three isotypes of light chains.

Immunoglobulin producing cells in the spotted wolffish (Anarhichas minor Olafsen): localization in adults and during juvenile development.

The presence of immunocompetent cells was studied in the larval and adult stages of the spotted wolffish, Anarhichas minor. In situ hybridization with a probe complementary to the secretory Igmu-chain was used to localize immunoglobulin producing cells or plasma cells in organs from adult fish and the appearance of these cells in lymphoid tissues during juvenile development. Plasma cells were located in pronephros, spleen, gut, gills and skin of adult wolffish. In juveniles, the first plasma cells were detected in the kidney 1 week post-hatching and the appearance in other lymphoid organs was in the order spleen, gut and thymus. No plasma cells were detected in skin and gills during the sampling period of juveniles (<10 cm). Our study confirmed that plasma cells are present in both the systemic and mucosal compartments of adult fish but during ontogeny there is an earlier appearance of plasma cells in the gut compared to gill and skin compartments.