Tissue preference of some myxobolids (Myxozoa: Myxosporea) from the musculature of European freshwater fishes

Abstract

For several species of fish myxosporeans known at present, the musculature has been designated as the location of intrapiscine development. In the majority of these cases, plasmodia and spores are actually found in the muscle cells, but there are also myxosporeans that select intermuscular connective tissue, fish bones, nerves and capillaries of the musculature as their site of development. During the plasmodial development of Myxobolus, Henneguya and Thelohanellus species in fish inhabiting Hungarian freshwaters, 3 main locations of development inside the muscles were identified. Pseudodispar-type plasmodia, such as M. cyprini, M. musculi and M. pseudodispar, form plasmodia intracellularly in the muscle cells, while the plasmodia of M. pfeifferi, M. sandrae and T. hovorkai develop in the intermuscular connective tissue. A similar development in the connective tissue of the ventricle and the bulbus arteriosus was observed for M. dogieli, a heart parasite found in some cyprinid fishes. The third type of development is represented by M. tauricus, which prefers the collagenous elements of the fin rays, but its plasmodia are commonly found in the muscle attached to the fish bones.