Parasite fauna of lanternfish (Myctophidae) in the Canary Islands, with an assessment of the role of myctophids in cetacean parasite transmission

Myctophids act as a key link between lower and higher trophic levels in oceanic systems, thus they are expected to play an important role in the life cycles of helminths of cetaceans, but evidence about this role is scarce. To fill this gap, we examined the parasitic fauna of 380 myctophids belonging to 11 species collected from waters off the Canary Islands, which is considered a hotspot for cetaceans. We also analysed the stomach contents of myctophids to identify prey that could act as intermediate hosts, and compiled dietary information on cetaceans to assess the role of myctophids in the transmission to definitive hosts inhabiting the Canary Islands. The copepod Cardiodectes bellottii, the digenean Lethadena profunda, the acanthocephalan Neorhadinorhynchus sp., as well as larvae of 5 helminths specific to cetaceans, i.e. Anisakis simplex s.s., Skrjabinisakis physeteris, S. brevispiculata, Pseudoterranova ceticola and Bolbosoma vasculosum, were detected. Stomach contents were dominated by crustaceans, especially copepods and euphausiids, which are known to act as intermediate hosts at least for Anisakis spp. and Bolbosoma spp. Based on cetacean dietary data, we hypothesize that myctophids could directly transmit A. simplex s.s. to piscivorous cetaceans, whereas S. physeteris, S. brevispiculata and P. ceticola, could be transmitted to teuthophagous cetaceans mainly through cephalopods (especially Histioteuthis spp.) that prey on myctophids. The role of myctophids in the transmission of B. vasculosum is unclear. Based on data from this and previous studies, only species of Anisakis, Skrjabinisakis, Pseudoterranova and Bolbosoma have been reported from myctophids worldwide. Whether this group of fish is involved in the life cycle of other helminths infecting cetaceans remains an open question.