New species of Kudoa Meglitsch, 1947 (Cnidaria: Myxozoa) infecting the swim bladder musculature of Batrachoides surinamensis (Bloch & Shneider) (Batracoidiformes: Batrachoididae).

The genus Kudoa is an important group of parasites within the class Myxozoa, as some species infect a wide range of fish hosts and cause post-mortem myoliquefaction, resulting in significant economic losses. This study describes a new species of Kudoa in toadfish Batrachoides surinamensis. In 60 % of specimens of B. surinamensis collected in the eastern Amazon, elongated white plasmodia were observed in the swim bladder muscle. Subquadrate myxospores measuring 5.6 µm in length, 7.5 µm in width, and 5.5 µm in thickness were recorded, with four polar capsules measuring 2.5 µm in length and 1.5 µm in width. Morphologically and morphometrically, these myxospores differ from those of other Kudoa species found in Amazonian fish. Histopathological analysis revealed that compression caused by plasmodia in muscle fibers, although no inflammatory infiltrates were observed. The Small subunit ribosomal (SSU) DNA sequence showed 97% similarity with a p-distance of 1.3% from K. viseuensis. In phylogeny, the new species formed a subclade with the species described in the Brazilian Amazon that infects fish from both marine and freshwater environments. The novel infection site, along with the morphological and molecular characteristics, supports the designation of a new species infecting the swim bladder musculature of B. surinamensis.