Experimental identification of the actinosporean stage of Sphaerospora renicola Dykova & Lom 1982 (Myxosporea : Sphaerosporidae) in oligochaete alternate hosts

The extrapiscine development of Sphaerospora renicola, a myxosporean parasi te of the kidney of common carp, Cyprinus carpio L., was studied in the exp erimentally infected oligochaetes Tubifex tubifex (Muller) and Branchiura s owerbyi (Beddard). After the infection of these tubificids with homogenized common carp kidneys containing myxospores of S. renicola, the development of actinosporean stages was first observed under light microscopy 8 days af ter infection in pathogen-free T. tubifex. Infection of B, sowerbyi with ma ture actinosporean stages was first observed 91 days after infection. At th at stage of development, pansporocysts containing neoactinospores filled th e intestinal epithelium of the worm. Ninety-five days after infection, pans porocysts containing actinospores and free actinospores were found in the g ut lumen of B. sowerbyi. Actinospores of S. renicola emerged from B. sowerb yi after 98 days of intraoligochaete development. These were floating in th e water and showed the typical form of neoactinospores. The shape of the sp ores was triangular in apical view and elliptical in lateral view. The prev alence of infection reached 37%. Control specimens of B. sowerbyi proved to be free of neoactinospores. Except for a single specimen of B. sowerbyi, t he only early developmental stages (pansporocysts) were found in T. tubifex .