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Atlantic cod displays a range of phenotypic and genotypic variations, which includes the differentiation into coastal stationary and offshore migratory types of cod that co-occur in several parts of its distribution range and are often sympatric on the spawning grounds. Differentiation of these ecotypes may involve both historical separation and adaptation to ecologically distinct environments, the genetic basis of which is now beginning to be unravelled. Genomic analyses based on recent sequencing advances are able to document genomic divergence in more detail and may facilitate the exploration of causes and consequences of genome-wide patterns. We examined genomic divergence between the stationary and migratory types of cod in the Northeast Atlantic, using next-generation sequencing of pooled DNA from each of two population samples. Sequence data was mapped to the published cod genome sequence, arranged in more than 6000 scaffolds (611 Mb). We identified 25 divergent scaffolds (26 Mb) with a higher than average gene density, against a backdrop of overall moderate genomic differentiation. Previous findings of localized genomic divergence in three linkage groups were confirmed, including a large (15 Mb) genomic region, which seems to be uniquely involved in the divergence of migratory and stationary cod. The results of the pooled sequencing approach support and extend recent findings based on single-nucleotide polymorphism markers and suggest a high degree of reproductive isolation between stationary and migratory cod in the North-east Atlantic.

The Atlantic cod (Gadus morhua) is a key species in the North Atlantic ecosystem and commercial fisheries, with increasing aquacultural production in several countries. A Norwegian effort to sequence the complete 0.9Gbp genome by the 454 pyrosequencing technology has been initiated and is in progress. Here we review recent progress in large-scale sequence analyses of the nuclear genome, the mitochondrial genome and genome-wide microRNA identification in the Atlantic cod. The nuclear genome will be de novo sequenced with 25 times oversampling. A total of 120 mitochondrial genomes, sampled from several locations in the North Atlantic, are being completely sequenced by Sanger technology in a high-throughput pipeline. These sequences will be included in a new database for maternal marker reference of Atlantic cod diversity. High-throughput 454 sequencing, as well as Evolutionary Image Array (EvoArray) informatics, is used to investigate the complete set of expressed microRNAs and corresponding mRNA targets in various developmental stages and tissues. Information about microRNA profiles will be essential in the understanding of transcriptome complexity and regulation. Finally, developments and perspectives of Atlantic cod aquaculture are discussed in the light of next-generation high-throughput sequence technologies.

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