Description of novel myxozoan and microsporidian parasites from cultured red seabream Pagrus major exhibiting mild scoliosis, with additional detection of the myxosporean in yellowback seabream Evynnis tumifrons

Red seabream Pagrus major (Temminck & Schlegel, 1843) (Teleostei: Sparidae) farmed in Japan exhibited mild scoliosis, and myxosporean and microsporidian parasites were isolated from the brain and medulla oblongata of the diseased fish, respectively. Based on the morphological and molecular analyses, the myxosporean specimens were described as a new species, Myxobolus tai n. sp. (Bivalvulida: Myxobolidae). The spore is oblong to oval in valvular view, with two pyriform polar capsules of slightly unequal size. Polar capsules are asymmetrically positioned relative to the major axis of the spore. Myxospores morphologically similar to those of M. tai were also identified in the kidney of the yellowback seabream Evynnis tumifrons (Temminck & Schlegel, 1843) (Sparidae) caught in North Pacific off Minami-Ise Town, Mie Prefecture, Japan. Whereas white and round plasmodia were observed in the brain of P. major , only free spores were confirmed in the kidney of E. tumifrons . Nucleotide sequences of the partial small subunit ribosomal RNA gene were identical between those myxosporeans collected from P. major and E. tumifrons , indicating they are conspecific. Molecular phylogenetic analysis revealed M. tai n. sp. is sister to Myxobolus iwagiensis Kawano, Sakurai, & Yanagida, 2025, which was described from the nervous tissues of wild southern medaka Oryzias latipes (Temminck & Schlegel, 1846) (Beloniformes: Adrianichthyidae) collected from brackish water in Japan. Molecular phylogenetic analysis revealed that the microsporidian in the medulla oblongata of P. major as an undescribed species belonging to the family Spragueidae. • Mild scoliosis was observed in red seabream farmed in Japan. • Myxosporean or microsporidian infection was confirmed in the central nervous system. • The myxosporean was identified as a new species belonging to the genus Myxobolus. • The same species was also identified in the kidney of the yellowback seabream. • The microsporidian was identified as an undescribed species of the family Spragueidae.