El-Matbouli M ; Holstein TW ; Hoffmann RW ;

Parasitol Res vol. 84 (9)   pp. 694-9, Sep 1998

Institute of Zoology, Fish Biology and Fish Diseases, University of Munich, Germany. melmatbouli@ucdavis.edu

Myxobolus cerebralis (Myxozoa: Myxosporea) has a complex two-host life cycle, which begins when waterborne triactinomyxon spores released from the infected oligochaete Tubifex tubifex contact a susceptible trout. Upon contact the triactinomyxon spores attach to the fish and release their sporoplasm cells into the epidermis. At approximately 50 days postinfection, sporogenesis begins, resulting in a large number of M. cerebralis spores in the cartilage of infected fish 6 weeks later. The spores of M. cerebralis can be released from infected fish only after the fish die or are eaten by predators. In both cases, spores released into the aquatic environment can be ingested by oligochaete worms of the species T. tubifex and then develop into the actinosporean triactinomyxon stage in the intestine within about 3 months. The triactinomyxon is the only stage infectious for salmonid fish. We determined the DNA concentration in sporoplasm cells, capsulogenic cells, and valvogenic cells of M. cerebralis spore stages from the trout and of triactinomyxon spore stages from T. tubifex. DNA was visualized using the DNA-specific fluorescent stain DAPI. Our results demonstrate that meiosis occurs only once in the developmental cycle of M. cerebralis in contrast to the previously published hypothesis. This takes place within the pansporocyst found in T. tubifex. Thereafter, the sporoplasm cells of the triactinomyxon spores in T. tubifex and M. cerebralis in trout are diploid.

Animal ;  Cell Nucleus: chemistry: ultrastructure ;  DNA,Protozoan: analysis ;  Fish Diseases: parasitology ;  Life Cycle Stages ;  Oligochaeta: parasitology ;  Oncorhynchus mykiss: parasitology ;  Parasitic Diseases,Animal: parasitology ;  Protozoa: cytology: pathogenicity: physiology ;  Spores ;  2050 ;