Co-existence of Myxobolus spp. (Myxozoa) in gray mullet (Mugil cephalus) juveniles from the Mediterranean Sea.

Gray mullet (Mugilidae) occur in all seas and are farmed widely around the world, and thus, the risk of their parasites spreading through transport of aquaculture seed is a serious concern. Among others, gray mullets typically host a diversity of myxosporeans, a group in which spore morphometrics of genera has been consistently shown to be inadequate for determination of species. In this study, we investigated Myxobolus Bütschli 1882 (Myxosporea) species found in two fingerling stocks of Mugil cephalus caught in the wild off the coasts of the eastern (Israel) and western (Spain) Mediterranean. Although we observed similar morphological features, significant dissimilarities in spore size and differences in Myxobolus species SSU rDNA sequences were noted. Genetic analyses demonstrated that multiple Myxobolus species, some with SSU rDNA sequences new to GenBank, infected the stock from Spain. In addition, Myxobolus DNA was found associated with several types of host tissue (gill, tail, and internal organs), and sequence analyses indicated that multiple species of Myxobolus were also present, sometimes in different tissues from the same fish. The results suggest that the gray mullets supported a collection of several different Myxobolus species with similar morphology.