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

Chemoreception through olfaction regulates essential fish behaviors, including reproduction. Fish olfactory receptor repertoire comprises four multigene families (olfactory receptors class C (OlfC), odorant receptor (OR), olfactory receptors class A (ORA), and trace amine-associated receptors (TAAR)), whose diversity strongly shapes species-specific olfactory capabilities. Here, we characterized the olfactory repertoire of the flatfish Solea senegalensis using a comparative orthology-based approach across eight fish species. We identified 455 olfactory receptor genes in S. senegalensis, including prominent expansions of the OlfC and TAAR families, representing the largest olfactory receptor repertoire among the species analyzed. Transcriptomic data supported the functional activity of 426 genes of the total repertoire, detected as expressed in the olfactory organ. Phylogenetic and synteny analyses revealed conserved genomic organization primarily among flatfish and lineage-specific expansions associated with clustered paralogs across multiple chromosomes in S. senegalensis. These findings highlight the expanded olfactory receptor repertoire in S. senegalensis, emerging as a promising model for studying chemoreception and addressing the reproductive-related challenges in aquaculture.