Warm water treatment increased mortality risk in salmon.

Thermal treatment is a controversial method to control sea lice in the Atlantic salmon farming industry. This study aimed to complement the growing evidence base to document the impact of thermal treatments on salmon welfare, behaviour, physiology and health. Here, fish were treated two times (four weeks apart) for 30 s in either 27, 30, or 33 °C warm water, and parameters were compared to a procedural control (exposed to their holding temperature of 14 °C) or a negative control (where no treatments were applied). The fish had a clear behavioural response to the warm water, despite low difference between treatment and holding temperature (Δt = 13, 16 or 19 °C). Eye damages were more prevalent in the warm water treated groups than in the controls. Little difference was recorded between treatment groups in their growth and condition factor, blood plasma values, organ health, and long-term coping ability. There was, however, a significant increase in mortality as a function of temperature after the first treatment (14 °C: 6.5%, 27 °C: 5.3%, 30 °C: 12.4% and 33 °C: 18.9% mortality). The first treatment was performed only two weeks after the fish had been tagged and moved into the experimental holding tanks, while the fish had been allowed to recover for four weeks without any handling before the second treatment. The group of fish that were not subjected to any treatments (the negative control) had no mortality throughout the entire experimental period.

Francisella noatunensis in Atlantic cod (Gadus morhua L.); waterborne transmission and immune responses.

This is the first report that confirms waterborne transmission of francisellosis in Atlantic cod. To investigate the transmission of disease, particle reduced water was transferred from a tank with intraperitoneally infected cod to a tank with healthy cod. Waterborne transmission of Francisella noatunensis was confirmed in the effluent group using immunohistochemistry and real-time quantitative PCR (RT-qPCR). The bacteria were located inside the accumulated macrophage-like cells. Specific and high antibody responses against live and inactivated bacteria were observed. Oil adjuvant had no effect on the antibody responses against inactivated F. noatunensis compared to saline formulation. The antigen epitope was a 20-25 kDa component of F. noatunensis suggested to be lipopolysaccharide detected by Western blot, Sypro Ruby and Silver staining. Systemic immune reactions were investigated by measuring the expression of IFN-γ, IL-1ß and IL-10 genes with RT-qPCR. After i.p. injection of live bacteria, a significant up-regulation of IFN-γ and IL-1ß expression was observed from 15 to 60 days post infection in spleen and head kidney. In intestine, IFN-γ was significantly up-regulated after 30 days whereas rectum showed no significant differences in expression. Elevated expression of IL-10 was observed in all the organs tested but was only significantly up-regulated at 60 days post infection in intestine from i.p. infected fish. For the cohabitant group, IL-1ß and IFN-γ was up-regulated in spleen whereas intestine and rectum showed a down-regulation after 60 days. IL-10 was up-regulated in intestine of cohabitant fish from day 30 to day 60. These results indicate that F. noatunensis infection provokes both specific antibody responses and long term inflammatory responses in cod. The present study provides new knowledge about infection routes and shows that both humoral and cellular defence mechanisms are triggered by F. noatunensis in cod.

Immunological differences in intestine and rectum of Atlantic cod (Gadus morhua L.).

The defence system of the distal gut (hindgut and rectum) of Atlantic cod, (Gadus morhua L.) was studied using (immuno)histochemical, electron microscopical and real-time quantitative PCR techniques. The uptake and transport of macromolecules in the intestinal epithelium was also investigated. In this study we observed that cod has many and large goblet cells in its intestinal epithelium and that IgM(+) cells are present in the lamina propria and their number is considerably higher in the rectum than in the intestine. Myeloperoxidase staining revealed low numbers of granulocytes in and under the epithelium of the distal intestine, whereas high numbers were found clustered in the submucosa of the rectum. Electron microscopy not only confirmed these observations, but also revealed the presence of lymphoid cells and macrophages within the intestinal epithelium. Acid phosphatase staining demonstrated more positive macrophage-like cells in the rectum than in the distal intestine. Antigen uptake studies showed a diffused absorption of horse radish peroxidase (HRP) and LTB-GFP, whereas ferritin uptake could not be detected. Basal gene expression of cytokines (IL-1beta, IL-8 and IL-10) and immune relevant molecules (hepcidin and BPI/LPB) were compared in both the intestine and rectum and revealed approximately 2-9 times higher expression in the rectum, of which IL-1beta expression showed the most prominent difference. The present results clearly indicate that intestinal immunity is very prominent in the rectum of cod.

Comparison of antibody responses in Atlantic cod (Gadus morhua L.) to Vibrio anguillarum, Aeromonas salmonicida and Francisella sp.

Bacterial diseases such as vibriosis, atypical furunculosis and francisellosis, are registered as an increasing problem in cod farming in Norway. In order to develop efficient vaccines against diseases it is of interest to investigate if the cod immune system differentiates between various serotypes of Vibrio anguillarum and variants of Aeromonas salmonicida associated with the diseases by raising specific antibody responses. Cod of the same origin were shown to raise significant responses to V. anguillarum, A. salmonicida and the intracellular bacteria Francisella sp. Individual responses to V. anguillarum or A. salmonicida varied from none to high responses, while all individuals immunised with Francisella revealed a significant response. The cod immune system appeared in some degree to distinguish between V. anguillarum serotypes and A. salmonicida variants. Although all bacteria had induced significant antibody responses detectable in whole cell ELISA, only some had induced antibodies with specificity to linear O-polysaccharide epitopes on blot.

Viral and bacterial diseases of Atlantic cod Gadus morhua, their prophylaxis and treatment: a review.

This review summarises the state of knowledge of both viral and bacterial diseases of Atlantic cod Gadus morhua, and their diagnosis, prophylaxis and treatment. The most important losses have been at the larval and juvenile stages, and vibriosis has long been the most important bacterial disease in cod, with Listonella (Vibrio) anguillarum dominant among pathogenic isolates. Vaccination of cod against pathogens such as L. anguillarum and Aeromonas salmonicida clearly demonstrates that the cod immune system possesses an effective memory and appropriate mechanisms sufficient for protection, at least against some diseases. Well-known viruses such as the nodavirus that causes viral encephalopathy and retinopathy (VER), infectious pancreatic necrosis virus (IPNV) and viral haemorrhagic septicaemia virus (VHSV) have been isolated from Atlantic cod and can be a potential problem under intensive rearing conditions. No commercial vaccines against nodavirus are currently available, whereas vaccines against IPNV infections based upon inactivated virus as well as IPNV recombinant antigens are available. A number of investigations of the pharmacokinetic properties of antibacterial agents in cod and their efficacy in treating bacterial infections have been reviewed.

Respiratory burst activity of Atlantic cod (Gadus morhua L.) blood phagocytes differs markedly from that of rainbow trout.

In the present study we investigated the respiratory burst (RB) activity of Atlantic cod (Gadus morhua L.) blood phagocytes and we evaluated how the RB activity of cod blood cells differ from that of trout. The RB activities were measured directly from highly diluted whole blood as luminol-amplified chemiluminescence (CL) under various conditions. Studies regarding the blood dilutions for cod whole blood chemiluminescence measurements (WBCL) revealed that at a final blood dilution of 1.5 microl ml(-1) or less the CL response was strictly proportional to the number of phagocytes. This range of blood dilution did not markedly differ from that of trout. However, the opsonisation capacity of cod plasma was markedly poorer. The RB activity of phagocytes was most active at 15 degrees C when heterologous cod serum was used as a source of opsonin, whereas at final blood dilution of 8.0 microl ml(-1) (when homologous cod plasma was at a higher concentration) the highest RB activity was observed at 10 degrees C. Aeromonas salmonicida strain MT004 (As MT004) induced higher RB activity than the two known pathogens for cod, atypical A. salmonicida and Vibrio anguillarum. Cod blood phagocytes were more responsive to plastic surfaces and the adhesion response of phagocytes was partly inhibited but did not totally vanish even at a final gelatin concentration of 0.4%. Moreover, cod serum enhanced the adherence of phagocytes and cod blood phagocytes also showed slow spontaneous degranulation. Finally, within the tested anticoagulants (heparin, Na-citrate, EDTA) heparin treated blood phagocytes generated the highest RB activity.