A closer look at Cryptobia dahli: a parabodonid flagellate from the stomach of the Atlantic lumpfish

Cryptobia dahli is a biflagellated endocommensal parabodonid, commonly found in the stomach of the Atlantic lumpfish, Cyclopterus lumpus. The SSU rDNA sequence obtained for C. dahli is the first gastric Cryptobia to be sequenced from fish, and in phylogenetic analyses it is robustly grouped with Cryptobia helicis an endocommensal from the reproductive system of land snails, and the type species of the genus, along with free-living Parabodo spp. This grouping forms as a sister clade to the parasitic haemoflagellates, Cryptobia spp. and Trypanoplasma borreli. This grouping lends support for a more clear distinction to be assigned between the haematozoic parasitic forms (Trypanoplasma spp.) and the endocommensal forms from the digestive system of fishes and reproductive system of land snails (Cryptobia spp.). The prevalence in wild caught adult lumpfish from Iceland was 100% with high numbers of flagellates present in all fish. Histological sections of stomach tissues from fish with high numbers of flagellates in their stomach contents were not found to cause any pathological changes to the stomach epithelium, suggesting that this flagellate will not become problematic in the future development of lumpfish culture for the aquaculture industry.