2.4 RNA extraction and sequencing
To estimate the coverage rate of the assembled genome over gene regions and to predict gene models, RNA-seq was performed to generate transcript data for multiple tissues, including the brain, muscle, liver, spleen, olfactory organ, retina, and gonad tissues collected from the same individual. RNA was extracted separately using Trizol Reagent (Invitrogen, Camarillo, USA), and RNA quality was checked using a Nanodrop spectrophotometer (Labtech, Ringmer, UK). The RNA was used to construct the Illumina RNA-seq library as described in a previous study (Zhu et al. 2014). These transcript libraries were sequenced using an Illumina NovaSeq 6000 in PE150 mode (Illumina Inc., San Diego, CA, USA).