Abstract : Rainbow trout, Oncorhynchus mykiss, is an important aquaculture species worldwide and, in addition to being of commercial interest, it is also a research model organism of considerable scientific importance. Because of the lack of a whole genome sequence in that species, transcriptomic analyses of this species have often been hindered. Using next-generation sequencing (NGS) technologies, we sought to fill these informational gaps. Here, using Roche 454-Titanium technology, we provide new tissue-specific cDNA repertoires from several rainbow trout tissues. Non-normalized cDNA libraries were constructed from testis, ovary, brain and gill rainbow trout tissue samples, and these different libraries were sequenced in 10 separate half-runs of 454-Titanium. Overall, we produced a total of 3 million quality sequences with an average size of 328 bp, representing more than 1 Gb of expressed sequence information. These sequences have been combined with all publicly available rainbow trout sequences, resulting in a total of 242,187 clusters of putative transcript groups and 22,373 singletons. To identify the predominantly expressed genes in different tissues of interest, we developed a Digital Differential Display (DDD) approach. This approach allowed us to characterize the genes that are predominantly expressed within each tissue of interest. Of these genes, some were already known to be tissue-specific, thereby validating our approach. Many others, however, were novel candidates, demonstrating the usefulness of our strategy and of such tissue-specific resources. This new sequence information, acquired using NGS 454-Titanium technology, deeply enriched our current knowledge of the expressed genes in rainbow trout through the identification of an increased number of tissue-specific sequences. This identification allowed a precise cDNA tissue repertoire to be characterized in several important rainbow trout tissues. The rainbow trout contig browser can be accessed at the following publicly available web site (http://www.sigenae.org/).