Evaluation of Immune Status in Two Cohorts of Atlantic Salmon Raised in Different Aquaculture Systems (Case Study)

Abstract

Assessment of immune competence of farmed Atlantic salmon is especially important during smoltification and the first several months in the sea. Recently developed tools were applied to salmon raised in a traditional flow-through facility (FT, cohort 1) and in a recirculation aquaculture system (RAS, cohort 2). Fish were sampled at four time-points: parr, smolt, and at three weeks and three months after seawater transfer (SWT); expression of 85 selected immune and stress genes, IgM transcripts (Ig-seq), and circulating antibodies were analyzed. A steady increase in gene expression was seen over time in gill and spleen in both cohorts, and especially in antiviral and inflammatory genes in the gill. Differences between the cohorts were greatest in the dorsal fin but later leveled off. Comparison with a gill reference dataset found a deviation in only three of 85 fish, suggesting a good immune status in both cohorts. Levels of both specific and nonspecific antibodies were higher in cohort 2 in smolts and in growers three weeks after SWT; however, levels evened out after three months in the sea. Ig-seq indicated association between antibody production, expansion of the largest clonotypes, and massive migration of B cells from spleen to gill in smolts. The results suggested greater agitation and higher reactivity of the immune system in RAS-produced salmon, but the difference between the cohorts leveled off over time.

Microalgae as functional feed for Atlantic salmon: effects on growth, health, immunity, muscle fatty acid and pigment deposition

“…45 genes with tissue specific regulation were selected from an established gene set composed of key immune and stress regulated genes in Atlantic salmon (Krasnov et al, 2020;Lund et al, 2022;Supplementary Table 4). We extended this set by three immunogene-specific primers derived for hamp, saa5 and sod1 (Supplementary Table 4).…”

Salinity change evokes stress and immune responses in Atlantic salmon with microalgae showing limited potential for dietary mitigation

“…However, these alterations in transcript levels were rather modest, possibly due to the transfer within the protected RAS environment with a lower pathogen pressure than the open marine environment. Due to different experimental setups, it is difficult to compare our results with other studies investigating freshwater to seawater transfer ( Johansson et al, 2016 ; Karlsen et al, 2018 ; Lund et al, 2022 ), but the general pattern of gene expression is similar.…”

“…Gene expression profiling allows the detection of both systemic and local immune responses in key immune organs. Recent studies on Atlantic salmon have revealed a variety of genes that can be used to assess the salmon’s immune status ( Krasnov et al, 2020 ; Lund et al, 2022 ). Accordingly, expression analysis of stress- and immune-related genes can complement traditional indicators such as growth performance, organ health and plasma indicators.…”