2.6 Total RNA extraction
Total RNA was extracted from the pool of four gill arches sampled in each individual. Before RNA extraction, the gills were rinsed in 1X PBS to wash out previous storage traces and a Nucleospin® RNA kit was used to extract total RNA following the manufacturer’s instructions (Machery-Nagel, Germany). Purity and concentration of the total RNA was checked using the NanoDrop™ One Spectrophotometer (Thermo Scientific, Waltham, MA, USA). The integrity of RNA was assessed using the Agilent 2100 Bioanalyzer (Thermo Scientific, Waltham, MA, USA). All samples passed the quality control threshold with RNA integrity numbers > 7.