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

In this study, we employed a 44K microarray approach to analyse the hepatic transcriptomic response of post smolt Atlantic salmon subjected to control conditions (12°C, ~100% air saturation), an incremental increase in temperature (12°C to 20°C; 1°C per week) under normoxia (~100% air saturation) or moderate hypoxia (~70% air saturation). Significance Analysis of Microarrays (FDR < 5%) identified 1900 and 2105 differentially expressed probes (DEPs) in salmon exposed to either Warm&Normoxic (WN) or Warm&Hypoxic (WH) conditions as compared with those maintained under control conditions (CT). Further, we found that heat stress alone or in combination with hypoxia caused most similar transcriptional responses and 1,111 (38%) DEPs were shared between WN and WH treatment groups. Consequently, in this study a unique set of 2,894 DEPs was determined. Atlantic salmon were exposed to following treatments: (1) Control (CT) constant temperature of 12°C and 100 % air saturation; (2) Warm&Normoxic (WN) incremental temperature increase (1°C per week from 12 - 20°C) at 100% air saturation; and (3) Warm&Hypoxic (WH) decrease in oxygen content of 70% air saturation over one week, followed by two weeks of acclimation to this oxygen level, and then incremental temperature increase (1°C per week from 12 - 20°C) at 70% air saturation. Liver samples were taken from 8 fish per treatment group (Ct,WN, and WH) at 20°C after 3 days. A universal reference design was used for the microarray experiment. For the test samples, RNA was used from individual livers of 6 fish from the 3 treatment groups. For each treatment group we used 6 biological replicates (3 fish from 2 tank replicates). All test samples were labeled with Cy5. The common reference was a pool of 18 RNA samples from livers of fish from all individuals involved in microarray experiment. The common reference was labeled with Cy3. Each individual test sample was hybridized together with the common reference sample on an array, so the experiment consisted of 18 arrays.