Extrapiscine development of Myxobolus drjagini Akhmerov, 1954 (Myxosporea: Myxobolidae) in oligochaete alternative hosts.

The extrapiscine development of Myxobolus drjagini, a myxosporean parasite of the head, operculum and buccal cavity of the silver carp (Hypophthalmichthys molitrix), was studied in experimentally infected oligochaetes, Tubifex tubifex. After infection of uninfected tubificids with mature spores of M. drajagini, development of actinosporean stages was first observed by light microscopy 27 days after infection. Triactinomyxon stages of M. drjagini emerged from the worms after 91 days of intraoligochaete development. In histological sections, early pansporocysts were found in the gut epithelium of the experimental oligochaetes 42 days after infection. Mature pansporocysts, each containing 8 triactinomyxons, appeared 79 days after infection. After rupture of the epithelial cell and the pansporocyst, free actinosporean stages were found in the gut lumen of the oligochaete. Actinosporean stages released from oligochaetes appeared in the water 91 days after infection. They were floating in the water and showed a typical triactinomyxon form. Each triactinomyxon had three pyriform polar capsules, a sporoplasm with 14 secondary cells inside the spore body, a moderately long style and slightly bent, trifurcated, conically ending tails. The total length of the triactinomyxon measured approximately 198 microns. The prevalence of infection in 51 oligochaetes proved to be 9.8%. No infection was found in the control oligochaetes.