Developmental changes in mitochondrial architecture in Myxobolus cuneus (Cnidaria: Myxozoa)

Myxobolus cuneus is a cnidarian parasite that infects multiple organs of Piaractus mesopotamicus in Brazilian fish farms. This study investigates mitochondrial architecture and its variation across developmental stages of the parasite by integrating transmission electron microscopy and in vivo confocal imaging. Thirty-eight fish specimens were examined, of which 32 (84%) were infected. Ultrastructural analysis revealed distinct mitochondrial morphologies associated with parasite development, with large mitochondria exhibiting well-developed cristae in the ectoplasmic region, and smaller mitochondria lacking cristae in mature myxospores. Confocal microscopy showed nuclear labeling but no detectable signal consistent with mitochondrial activity in mature myxospores, whereas immature stages exhibited labeling indicative of mitochondrial activity. Molecular analysis of the SSU rDNA (1867 bp) showed 100% sequence similarity to Myxobolus cf. cuneus, supporting their conspecificity. Together, these findings demonstrate stage-specific variation in mitochondrial architecture in M. cuneus and suggest a shift toward reduced mitochondrial function in mature myxospores. This study provides new ultrastructural data on mitochondrial architecture in M. cuneus, highlighting its variation across developmental stages.