High prevalence of Ichthyophonus sp. infections in Northeast Atlantic mackerel (Scomber scombrus)

Ichthyophonus spp. are cosmopolitan parasites causing prolifera-tive, systemic disease in a number of marine and freshwater fish, including several commercially important species such as Atlantic and Pacific herring (Clupea harengus, C. pallasii), rainbow trout (Oncorhynchus mykiss), Chinook salmon (O. tshawytscha) and sockeye salmon (O. nerka) (Gregg et al., 2016; Kocan et al., 2006; Rahimian & Thulin, 1996; Tierney & Farrell, 2004; Zuray et al., 2012). There is some uncertainty regarding both species diversity and host speci-ficity within the Ichthyophonus genus, and at present only two spe-cies have been formally described, I. hoferi Plehn and Mulsow (1911) from rainbow trout and I. irregularis Rand et al.,2000 from yellowtail flounder (Limanda ferruginea). There are, however, strong genetic indications that the genus comprises more species than the two de-scribed so far (Hershberger et al., 2016; Rasmussen et al., 2010).