Kudoa prunusi n. sp. (Myxozoa: Multivalvulida) from the brain of Pacific bluefin tuna Thunnus orientalis (Temminck & Schlegel, 1844) cultured in Japan

Kudoa prunusi n. sp. (Myxozoa; Multivalvulida) is described from the brain of Pacific bluefin tuna Thunnus orientalis cultured in Japan. Numerous white cysts, up to 0.5 mm in size, were found on and in the brain. Spores having typically five spore valves and five polar capsules resembled a five-petal cherry blossom in apical view and were conical shape with a round bottom in side view. Average spore size was 9.63 (8.5-10.3) μm in width and 7.50 (6.7-8.6) μm in length. The spore dimensions of K. prunusi overlapped with those of Kudoa yasunagai ex Sillago ciliata having five to six spore valves, but they were clearly distinct in spore shape, 18S rDNA and 28S rDNA sequences (0.3% and 1.7% differences, respectively). Phylogenetic analysis of 18S rDNA revealed that K. prunusi grouped with the brain-infecting multivalvulid species, K. yasunagai, K. chaetodoni, K. lethrini and K. neurophila, rather than five-valved Kudoa spp. Combined with morphological, molecular and biological differences, K. prunusi was proven to be a new species.

Research highlights► A new Kudoa myxozoan with five valves was found from brain of Pacific bluefin tuna. ► Combined morphological and molecular analyses characterized K. prunusi n. sp. ► Phylogenetic analysis showed that K. prunusi grouped with brain-infecting species. ► Analysis of 18S and 28S rDNA showed that K. prunusi was distinct from known species.