DAO 63:205-214 (2005)  -  doi:10.3354/dao063205

ABSTRACT: There is uncertainty regarding the validity of Myxobolus heterosporus Baker, 1963. The present study revises the taxonomy, using specimens isolated from plasmodia situated in the infected cornea of Oreochromis aureus, O. niloticus or Tilapia zillii inhabiting the River Nile, Egypt. In addition, histological effects of the parasite on the infected tissue were examined. The spores of M. heterosporus had a variety of shapes expressing remarkable heteromorphism. Five main Myxobolus-like spore types and tailed-spores were found. All forms were photographed, measured, sketched and described. Light and electron microscopy supported that spores of a Myxobolus-like morphology co-existed with so-called tailed-spores in one plasmodium. Some transitional stages from Myxobolus-like spore types to tailed-spores were observed. Therefore, some tailed-spores may be simply heteromorphs of Myxobolus.

KEY WORDS: Myxosporea · Revision · Myxobolus heterosporus · Heteromorphism · Plasmodium · Cornea · Oreochromis aureus · O. niloticus · Tilapia zillii · River Nile