Identification and characterization of Myxobilatus channi n. sp. (Cnidaria: Myxosporea) infecting the alimentary tract of northern snakehead Channa argus cultivated in China

The northern snakehead Channa argus is a freshwater fish of high economic importance in Asian countries. Intensive snakehead cultivation requires the regular addition of feedwater to ensure water quality, providing an opportunity for parasite transmission. However, the parasite composition of northern snakehead is still poorly studied. In a series of investigations conducted in China, a myxosporean species was isolated from the farmed northern snakehead. It manifested with a dense formation of ellipsoidal, proliferous cysts presenting along the wall of the intestine and pyloric caeca. The microorganism inside the cyst displayed elongate, pyriform, and bivalved myxospores, with an elongated caudal appendage extending from posterior extremity of each smooth shell valve. Two pyriform polar capsules were situated at a level perpendicular to the sutural plane. Based on these observations, the present isolates was assigned to the genus Myxobilatus. However, it was morphologically distinguishable from other congeners. Moreover, the same result was obtained according to a less than 92% top genetic identity observed in pairwise comparison. Therefore, we confirmed the present species new to science and designated it as Myxobilatus channi n. sp. Histologically, plasmodia bulging toward the mucosa were confined to the circular muscle layer, leading to epithelial sloughing and necrosis of the intestinal villi. Phylogenetically, M. channi n. sp. was positioned branching from those species belonging to the family Myxobilatidae, implicating the inability of morphological taxonomy to reflect the true evolutionary relationship among myxosporeans. This study enhances the understanding of the composition of the parasite infecting the northern snakehead that will inform future scrutiny and management of the parasite infection.