Striking olfactory receptor gene repertoire expansion in Senegalese sole ( Solea senegalensis )

Summary Chemoreception through olfaction is essential for regulating fish behaviour. Fish olfactory receptor repertoire comprises four multigene families (OlfC, OR, ORA and TAAR), whose diversity strongly shapes species-specific olfactory capabilities. In this study, the olfactory repertoire of the flatfish Solea senegalensis was characterized through orthology analysis with seven species, identifying 455 olfactory receptor genes in S. senegalensis , including large OlfC and TAAR gene expansions. Active functionality was shown in 426 genes of the total repertoire through the olfactory transcriptome and the RNA-seq libraries generated in this study, showing expression correlation within each family. Phylogenetic trees integrating orthologous and paralogous relationships, along with chromosomal locations were constructed. Notable synteny conservation was observed primarily among flatfish, partially lost with phylogenetically distant taxa. Olfactory receptor genes were heterogeneously distributed across twelve S. senegalensis chromosomes, constituting eleven major clusters of paralogous genes. Overall, S. senegalensis exhibits an expanded and specialized olfactory function, emerging as a promising model for studying chemoreception and addressing the reproductive issues in aquaculture.