Effect of environmental factors on survival and population growth of ciliated parasite, Mesanophrys sp. (Ciliophora: Scuticociliatia) infecting Portunus 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.

Keywords: Mesanophrys sp.; pH; population growth; salinity; scuticociliates; survival; temperature.

Fig. 1.

Survival rate % of Mesanophrys sp. at different temperatures. Different superscript letters represent significant differences among seven temperature groups (post hoc Bonferroni test; P < 0.01).

Fig. 2.

Population density of Mesanophrys sp. at different temperatures. Bar graph represents significant differences between different groups at each time point (post hoc Bonferroni test; P < 0.01).

Fig. 3.

Relationship between population growth rate and generation time at different temperatures. Different superscript letters represent significant differences among seven temperature groups (post hoc Bonferroni test; P < 0.01).

Fig. 4.

Effect of temperature on the body size of Mesanophrys sp. Different superscript letters represent significant differences among seven temperature groups (post hoc Bonferroni test; P < 0.01).

Fig. 5.

Survival rate % of Mesanophrys sp. at different salinities. Different superscript letters represent significant differences among groups (post hoc Bonferroni test; P < 0.01).

Fig. 6.

Population growth density of Mesanophrys sp. at different salinities. Bar graph represents significant differences between different groups at each time point (post hoc Bonferroni test; P < 0.01).

Fig. 7.

Relationship between population growth rate and generation time of Mesanophrys sp. at different salinities. Different superscript letters represent significant differences among groups (post hoc Bonferroni test; P < 0.01).

Fig. 8.

Effect of different salinities on the body size of Mesanophrys sp. Different superscript letters represent significant differences among groups (post hoc Bonferroni test; P < 0.01).

Fig. 9.

Survival rate % of Mesanophrys sp. at different pH. Different superscript letters represent significant differences among groups (post hoc Bonferroni test; P < 0.01).

Fig. 10.

Population density of Mesanophrys sp. at different pH. Bar graph represents significant differences between different groups at each time point (post hoc Bonferroni test; P < 0.01).

Fig. 11.

The population growth rate of Mesanophrys sp. at different pH. Different superscript letters represent significant differences among groups (post hoc Bonferroni test; P < 0.01).

Fig. 12.

Effect of pH on the body size of Mesanophrys sp. Different superscript letters represent significant differences among groups (post hoc Bonferroni test; P < 0.01).

Fig. 13.

Effect of frequency changes method and time on the population density of Mesanophrys sp. Bar graph represents significant differences between different groups at each time point (post hoc Bonferroni test; P < 0.01).

Fig. 14.

Effect of frequency changes method and time on the population growth rate of Mesanophrys sp. Bar graph represents significant differences between different groups at each time point (post hoc Bonferroni test; P < 0.01).