Morphological and molecular characterisation of Henneguya pallida n. sp. from the gills of the pale catfish, Rhamdia guatemalensis (Günther, 1864), in southern Mexico

During a survey on myxozoan parasites in fish from southern Mexico, myxospores from the genera <i>Henneguya</i> and <i>Myxobolus</i> were detected in the gills and mesentery of the pale catfish (<i>Rhamdia guatemalensis</i>). Identification of a <i>Henneguya</i> sp. in the gills was supported by histology, myxospore morphology, and molecular analyses of the 18S rDNA and 28S gene sequences. Histopathological examination revealed that the myxospore-forming plasmodia of <i>Henneguya</i> sp. were associated with the gill filaments. Phylogenetic analyses placed this species within a clade of <i>Henneguya</i> species infecting Siluriformes. In contrast, scattered myxospore aggregates found in the mesentery were examined solely through morphological criteria. Four different myxospore morphotypes belonging to the family Myxobolidae were identified in a single specimen of <i>R</i>. <i>guatemalensis</i>; however, molecular identification was unsuccessful; therefore, only brief taxonomic descriptions are provided. Based on morphological and molecular evidence, the <i>Henneguya</i> sp. from the gills is described as a new species, <i>Henneguya pallida</i> n. sp. Further samplings are needed to fully characterise the myxospores found in the mesentery.