Effect of environmental factors on survival and population growth of ciliated parasite,Mesanophryssp. (Ciliophora: Scuticociliatia) infectingPortunus trituberculatus

Abstract

Mesanophrys sp. is a newly identified parasitic ciliate infecting farmed swimming crab. To demonstrate the correlation between parasite development and environmental conditions, this study aimed to investigate the effect of temperature, salinity, pH and frequency of passage of parasite on survival, growth and body size of Mesanophrys sp. in vitro. The results revealed that survival, population density and growth rate of the parasite were highest at 12°C and decreased with increasing temperature from 16 to 26°C. In addition, the survival, population density and growth rate of Mesanophrys sp. were high at 20‰. When salinity was adjusted to levels lower (0–10‰) and higher (40–60‰) than 20‰, the parasite's survival and growth rate gradually declined. The optimal pH for parasite survival was 8.0, whereas its survival was inhibited at <4.5 or >9.5. Our result also showed that parasite body proportions (length:width) were significantly smaller at the highest temperature compared to the lower temperature, whereas different salinities had no significant effect. Furthermore, we introduced dynamic parasite culture systems in vitro where Mesanophrys sp. was cultured in medium-containing culture plates through continually reducing and halving the old medium into fresh. Application of this optimized dilution timing technique with fresh medium and sub-cultured enabled a continuous culture of parasites. Under this optimized condition, the highest population density and exponential growth rate of the parasite were achieved than that of a control group. This study will help to understand the ciliated parasite infection dynamics and provides new possibilities for in vitro parasite-associated studies.

Dynamic Distribution of Mesanophrys sp. and Tissue Enzyme Activities in Experimentally Infected Mud Crab Scylla paramamosain

“…Most Mesanophrys ciliates feed on bacteria and organic debris [7] and grow quickly through a two-division proliferation mode. However, they can also invade the hemolymphs of crustaceans and consume the lysate there in order to proliferate; intense infection causes damage to the internal organs and finally leads to death, which may cause serious economic losses to local farmers and enterprises [8][9][10][11]. In early 2017, a new parasite, Mesanophrys sp., emerged in an artificial nursery farm of Portunus trituberculatus in Ningbo, Zhejiang Province, resulting in more than 80% mortality among the P. trituberculatus [12].…”