Myxobolus pavlovskii from the gills of silver carp (Hypophthalmichthys molitrix) were used in attempts to transmit the infection under laboratory conditions. Spores of M. pavlovskii were placed in aquaria that contained sterilized sand and had been filled with tap water at 15-16 degrees C. Furthermore, oligochaetes (90% Tubifex tubifex) were added and examined by wet mounts and histology. Hexactinomyxon spores developed after about 3 months only in T. tubifex that had been exposed to M. pavlovskii. Myxosporea-free silver carp developed cysts in their gills that contained M. pavlovskii at 120 days after contact with Hexactinomyxon spores, proving that M. pavlovskii also needs an oligochaete intermediate host for its development.