Abstract
Hemorrhagic thelohanellosis of carp Cyprinus carpio is caused by Thelohanellus hovorkai (Myxozoa) whose life-cycle involves an alternate oligochaete host Branchiura sowerbyi. In this article, we aim to evaluate a potential vector control to minimize the impact of the hemorrhagic thelohanellosis in 2 methods: 1) ecological control of oligochaete fauna by soil amendment and 2) biological control of oligochaete abundance by benthos-eating fishes. In the first method, the oligochaete fauna was closely associated with the substrate characteristics of farm, where B. sowerbyi was highy abundant in an enriched pond. Laboratory studies on substrate preference of oligochaetes proved that B. sowerbyi preferred organic mud than sand, whereas non-susceptible oligochaetes (Limnodrillus socialis) had no substrate tropism. Further, morbitities and mortalities of B. sowerbyi rearing in sand were noted. It was also postulated that non-susceptible oligochaetes might act as a biofilter of T. hovorkai. Consequently, by replacing bottom substrate from mud to sand, a shift in oligochaete communities from B. sowerbyi to non-susceptible oligochaetes was suggested to be feasible. In the second method, loach (Misgurnus anguillicaudatus), which was T. hovorkai-resistant fish species, was indicated to be an effective predator of benthic invertebrates, possibly resulting in elimination of oligochaetes in culture ponds. We propose that a vector control by environmental and biological manipulation of benthic fauna is a promising strategy against myxosporean diseases.
