Morphological re-description and phylogenetic relationship of five myxosporean species of the family Myxobolidae infecting Nile tilapia.

Freshwater fish have a major economic and nutritional importance worldwide. Myxosporeans are highly dangerous parasites that infect different fish species, causing severe damage to a large number of economically important species, especially in aquaculture. We conducted a survey of myxosporean parasites infecting Nile tilapia Oreochromis niloticus (Perciformes: Cichlidae) collected from different localities along the River Nile passing through Giza province, Egypt. Out of 100 fish specimens collected, 45 were found to be naturally infected with these parasites in the region of the trunk kidney. Light microscopic examination revealed the presence of 5 distinct myxosporean species belonging to 2 different genera, viz. Myxobolus and Triangula, belonging to the family Myxobolidae; all 5 species have been previously described. Morphological characteristics, host specificity and geographical distribution, tissue tropism, and molecular analysis of the partial sequence of small subunit ribosomal DNA gene revealed that the recovered myxosporean species described herein were genetically distinct from other myxozoan species but had 95% sequence similarity to M. cerebralis. Also, phylogenetic analysis placed the present myxosporean species in the freshwater Myxobolus clade, which is a sister group of freshwater Myxobolus/Henneguya species.