Molecular characterization of CD9 and CD63, two tetraspanin family members expressed in trout B lymphocytes

•Two novel tetraspanin members have been identified in rainbow trout, homologues to mammalian CD9 and CD63.•Both CD9 and CD63 are constitutively expressed in different tissues.•These tetraspanins are differentially regulated in response to viral infection and vaccination.•In the early developmental stages, CD9 transcription is significantly increased after first feeding.•Trout IgM+ B lymphocytes transcribe both CD9 and CD63.