Gill tissue from each individual was homogenized and total RNA was extracted using an E.Z.N.A. Total RNA Kit I (Omega BIO-TEK Inc., Norcross, GA, USA) following the manufacturers instructions. Initial RNA yield and quality were assessed using a NanoDrop 2000 spectrophotometer (Thermo Scientific, Plaquemine, Louisiana, USA). Total RNA for 48 samples was sent to the University of Texas at Austins Genomics Sequencing and Analysis Facility where RNA integrity was confirmed using a 2100 Agilent Bioanalyzer and Tag-Sequencing libraries, which sequences the 3 end of the mRNA (Lohman et al., 2016; Meyer et al., 2011). The TruSeq libraries were sequenced on 2 lanes of an Illumina HiSeq 2500 platform producing 100bp single end reads