No abstract

Oil-adjuvanted vaccines reduce long-term growth in farmed Atlantic salmon Salmo salar, possibly via an increase in metabolic rate due to the energetic demands of the immune system. We tested this hypothesis by comparing sham-vaccinated to vaccinated smolts (total n = 2096, ca. 80 g) under different scenarios of water temperature (12 vs. 17°C, n = 1048 per temperature) and oxygen (O2) saturation (60, 70, 80, and 100%, n = 524 per O2 saturation level) in order to manipulate metabolic rate and O2 availability. We expected a more severe vaccination effect under conditions of high water temperature and low O2 saturation. Groups were kept in duplicate tanks under controlled temperature and hypoxia conditions for 7 wk post-vaccination before being transferred to uncontrolled common-garden natural conditions for 5 mo in a sea-cage. Body mass and length were recorded at the initiation and end of the controlled and uncontrolled environmental conditions. Vaccination and low O2 saturation at 17°C significantly reduced body mass (13 and 3% through vaccination and 9 and 20% through 60% O2 saturation at the end of the tank and sea-cage periods, respectively). However, there was no interaction between vaccination, temperature, and O2 saturation at the end of the tank or sea-cage period, lending no support to our hypothesis. A secondary observation was that emaciated ‘loser’ fish were mainly associated with the 17°C and low (mainly 60%) O2 saturation treatment. In conclusion, although vaccination led to a reduction in body mass, this effect was not influenced by environmental conditions expected to alter metabolic rate.

Haemorrhagic smolt syndrome (HSS) is a disorder of unknown aetiology causing losses in the fresh water phase of Atlantic salmon farming. Normally, the mortality is limited and symptoms disappear upon seawater exposure. In this case study, classical HSS pathology with internal organ haemorrhages and nephrocalcinosis was diagnosed, and the losses were substantial. Microarray analyses of head kidney revealed association between HSS and enhanced expression of stress genes and proteins reducing bioavailability of iron, heme, and retinol. In parallel, suppression of multiple metabolic pathways was observed. Up-regulation of genes encoding acute phase proteins, complement, and lectins indicated mild inflammation but without characteristic features of viral or bacterial infections. Microarray analyses highlighted several members of tumor necrosis factor receptor superfamily that may control development of B-cell immunity. Examination of IgM at the mRNA and protein levels showed the impact of HSS on vaccine responses. In fish without HSS symptoms (non-HSS), titres of vaccine specific antibodies to A-layer of Aeromonas salmonicida subsp. salmonicida and Moritella viscosa and antibodies binding to DNP-keyhole limpet hemocyanin (DNP-KLH), which are presumably polyreactive, were respectively four- and 14-fold higher than in HSS-diseased fish. Parallel sequencing of variable regions of immunoglobulin Mrevealed a larger size of most abundant clonotypes shared by multiple individuals in the non-HSS group. The results of the current case study indicated that, in addition to direct damage, HSS suppresses humoral immune responses including the production of specific and polyreactive antibodies.