The Transcriptomic Responses of Atlantic Salmon (Salmo salar) to High Temperature Stress Alone, and in Combination with Moderate Hypoxia

Abstract

Background: Increases in seawater temperatures and in the frequency and severity of hypoxic events are expected with climate change, and may become a challenge for cultured Atlantic salmon and negatively affect their growth, immunology and welfare. Thus, we examined how an incremental temperature increase alone (Warm & Normoxic-WN: 12→20°C; 1°C week-1), and in combination with moderate hypoxia (Warm & Hypoxic-WH: ~70% air saturation), impacted salmon’s hepatic transcriptome expression compared to control fish (CT: 12°C, normoxic) using 44K microarrays and qPCR. Results: Overall, we identified 2,894 differentially expressed probes (DEPs, FDR < 5%), that included 1,111 shared DEPs, while 789 and 994 DEPs were specific to WN and WH fish, respectively. Pathway analysis suggested that the cellular mechanisms affected by the two experimental conditions were quite similar, with up-regulated genes functionally associated with heat shock response, ER-stress, apoptosis and immune defence, while genes connected with general metabolic processes, proteolysis and oxidation-reduction were largely suppressed. The qPCR assessment of 41 microarray-identified genes validated that the heat shock response (hsp90aa1, serpinh1), apoptosis (casp8, jund, jak2) and immune responses (apod, c1ql2, epx) were up-regulated in WN and WH fish, while oxidative stress and hypoxia sensitive genes were down-regulated (cirbp, cyp1a1, egln2, gstt1, hif1α, prdx6, rraga, ucp2). However, the additional challenge of hypoxia resulted in more pronounced effects on heat shock and immune-related processes, including a stronger influence on the expression of 14 immune-related genes. Finally, robust correlations between the transcription of 19 genes and several phenotypic traits in WH fish suggest that changes in gene expression were related to an impaired physiological and growth performance. Conclusion: Increasing temperature to 20°C alone, and in combination with hypoxia, resulted in the up- and down-regulation of genes involved in similar important pathways in Atlantic salmon. However, the heat shock and immune responses of fish exposed to 20°C and hypoxia were more affected, and their transcriptional dysregulation was related to reduced performance. This study provides valuable information on how these two environmental challenges affect the expression of stress-, metabolic- and immune-related genes and pathways and identifies potential biomarker genes for improving our understanding of fish health and welfare.

ddRAD‐Seq reveals evolutionary insights into population differentiation and the cryptic phylogeography of Hyporhamphus intermedius in Mainland China

“…Such general relationships are not surprising given that in fishes, temperature is linked to key physiological, developmental, and behavioral processes, rendering fish highly sensitive to climatic and thermal conditions (Chen et al., 2018; Crozier & Hutchings, 2014). Stable and high temperature affects a broad spectrum of cellular components, accelerating enzymatic activity and metabolism in organism (Beemelmanns et al, 2021; Jesus et al, 2016; Jeffries et al, 2014). In GPA, we also found a difference in morphological traits (dorsal, anal fins rays, etc.…”

Acute and chronic cold exposure differentially affect cardiac control, but not cardiorespiratory function, in resting Atlantic salmon (Salmo salar)

“…However, chronic exposure to cold (∼0–1 °C) temperatures during the winter months, as well as acute daily drops in temperature (to < 2 °C) due to ‘turn over’ caused by rough conditions, are associated with large-scale mortalities at salmon sea-cages in these countries ( Círíc, 2020 ; CBC News, 2020 ; Huffman, 2019 ; The Canadian Press, 2015 ). Our understanding of how warm (summer) temperatures affect cultured Atlantic salmon has improved greatly over the past few years ( Anttila et al, 2014 ; Beemelmanns et al, 2020 , 2021 ; Gamperl et al, 2020 ; Gamperl and Syme, 2021 ; Hvas et al, 2017 ; Penney et al, 2014 ; Tromp et al, 2018 ). However, we have a very limited understanding of how the biology and physiology of this species is affected by short-term and long-term exposure to cold temperatures, and the results of this research can be contradictory (e.g., see Liu et al, 2020 vs. Sandnes et al, 1988 ).…”