Transcriptome characterization and SSR discovery in large-scale loach Paramisgurnus dabryanus (Cobitidae, Cypriniformes)

- Illumina sequencing generated 1.05 × 108 reads which resulted in 71,887 transcripts.
- Nr, Go, COG and KEGG function annotation was performed for the transcriptome.
- Transcriptome comparison analysis was performed with Danio rerio.
- We identified 15,106 SSRs, of which 400 SSRs were initially validated.
- Further polymorphism test of 41 SSRs showed that 36 (87.8%) loci were polymorphic.

The large-scale loach (Paramisgurnus dabryanus, Cypriniformes) is a bottom-dwelling freshwater species of fish found mainly in eastern Asia. The natural germplasm resources of this important aquaculture species has been recently threatened due to overfishing and artificial propagation. The objective of this study is to obtain the first functional genomic resource and candidate molecular markers for future conservation and breeding research. Illumina paired-end sequencing generated over one hundred million reads that resulted in 71,887 assembled transcripts, with an average length of 1465 bp. 42,093 (58.56%) protein-coding sequences were predicted; and 43,837 transcripts had significant matches to NCBI nonredundant protein (Nr) database. 29,389 and 14,419 transcripts were assigned into gene ontology (GO) categories and Eukaryotic Orthologous Groups (KOG), respectively. 22,102 (31.14%) transcripts were mapped to 302 KEGG pathways. In addition, 15,106 candidate SSR markers were identified, with 11,037 pairs of PCR primers designed. 400 primers pairs of SSR selected randomly were validated, of which 364 (91%) pairs of primers were able to produce PCR products. Further test with 41 loci and 20 large-scale loach specimens collected from the four largest lakes in China showed that 36 (87.8%) loci were polymorphic. The transcriptomic profile and SSR repertoire obtained in this study will facilitate population genetic studies and selective breeding of large-scale loach in the future.