This is the first study to quantify the periodic emergence of a Conchophthirus sp. from its bivalve host. Emergence rates of C. acuminatus from Dreissena polymolpha over the entire 24-day experiment appeared to be directly correlated with infection intensity. The rate of ciliate emergence from individual mussels varied considerably throughout the experiment at both 14°C and 21°C. It was not uncommon to have a sampling period in which no emergence was observed immediately followed by a period of high emergence, e.g., at 14°Cfrom 0 to 25 ciliates and at 21°C from 0 to 720 ciliates. The total mean number of ciliates that were observed to have emerged from each mussel during the 24-day experiment was significantly higher at 21°C (207 ciliates/mussel) than at 14°C (29 ciliates/mussel). Our experiments suggested that C. acuminatus have a short survival period outside their host. Although we observed a maximum survival period of 144 hr (6 days), most ciJiates died within 48 h.
Journal of Shellfish Research (2003) Volume 22, Issue 1: 495-500

We report the results of a two-year study in the Svisloch River (Minsk, Belarus) on the dynamics of infection in Dreissena polymorpha by nematodes and three ciliate species Conchophthirus acuminatus, Ophryoglena sp., and Ancistrumina limnica. Although these endosymbionts were present in most of the samples, their prevalence and infection intensity differed significantly. C. acuminatus and A. limnica infection intensities in both years of the study had a maximum in summer and were positively correlated with water temperature. In contrast, Ophryoglena sp. and nematode infection intensities were considerably lower in summer versus winter and were negatively correlated with temperature. In the first long-term study to monitor the size and reproductive rate of C. acuminatus, we found that mean length was negatively correlated with temperature and that temperature was positively correlated with asexual reproduction, with a peak of cell division in April as water temperatures increased.
Journal of Invertebrate Pathology (2003) Volume 83: 73–82

Host specificity, extremely high prevalence and infection intensity, and easy sampling make the mantle-cavity ciliate Conchophthirus acuminatus a very convenient model to address numerous fundamental questions relating to symbiosis and commensalism. The acquisition of food by the ciliate as a result of Dreissena filtration activity is probably the basis of the symbiosis, with additional benefits to C. acuminatus being shelter, provision of oxygen, and dispersal. The number of C. acuminatus in a Dreissena population depends on the mussel’s size-frequency distribution as there is a direct correlation between Dreissena size and infection intensity. Lack of a correlation between host density and commensal infection intensity may indicate that D. polymorpha and C. acuminatus have a different environmental optimum. Zebra mussels of a given length in each population may have their own carrying capacity of C. acuminatus infection intensity. Upon reaching this carrying capacity, a symbiont population may have density-dependent feedback mechanisms, which slow its reproduction rate within a host and/or increase its emigration from the mussel to maintain an optimal density within its host. Massive emergence of ciliates into open water may be synchronized with a mass occurrence of recently settled Dreissena juveniles to maximize the infection.
Journal of Shellfish Research (2007) Volume 26, Issue 4: 1153–1160