“…Although, transcriptome analysis has provided a new gateway for identifying levels of gene expression and new transcripts and has thus become a powerful tool for species that lack reference genome information, a comparison of mRNA expression levels, protein amounts, and enzymatic activities has revealed low correlations between metabolome and transcriptome, indicating that transcriptome analysis is insufficient to understand protein dynamics or biochemical regulation [15,16]. A more direct correlation is expected for proteins and biological processes [16], making quantitative mass spectrometric (MS) proteomics an attractive approach [17], and a relative quantification approach based on MS results is the ultimate way to go. Moreover, the isobaric tags for relative and absolute quantitation (iTRAQ) are demonstrated to be more reliable and accurate than two-dimensional differential gel electrophoresis and other proteomic methods in identifying and quantifying proteins [18], and have been increasingly applied to examine differentially expressed proteins in different aquatic animals, such as zebrafish (Danio rerio), marine medaka (Oryzias melastigma) and Chinese mitten crab Eriocheir sinensis, in response to different pathogens, i.e.…”