An infection mechanism of Balantidium ctenopharyngodoni, based on its prevalence and in vitro cultivation

Balantidium ctenopharyngodoni Chen, 1955 is an intestinal ciliate identified from the hindgut of grass carp (Ctenopharyngodon idella). Although it was described quite a long time ago, its epidemiologic features and growth characteristics remain poorly understood. In the present study, the investigation of B. ctenopharyngodoni presence was conducted in different age groups of grass carp, and we also developed a self-made medium (BCM medium) to cultivate B. ctenopharyngodoni in vitro. In the grass carp fed on plant-based diets, balantidia were not identified before the age-1, whereas they were identified in fish above the age-1. In the fishes fed on the granular fish meal we did not identify any balantidia regardless of the age of the fish (age-1+ or age-2). BCM medium was effective for in vitro cultivation of B. ctenopharyngodoni, and polysaccharides were an essential nutrient for its growth. We also proposed potential infection mechanisms of B. ctenopharyngodoni in the grass carp above two summers of age.