The influence of water temperature and pH on the survival of Fasciola hepatica miracidia

Experimental studies on the survival of Fasciola hepatica miracidia show no evidence that miracidial mortality varies with the pH of the medium, at least in the range 6. 0-8. 0. On the other hand, miracidial mortality is shown to vary with both the temperature of the medium and the age of the larvae. The mean expected life-span of the miracidium decreases from about 35 h at 6 °C to about 6 h at 25 °C. The Gompertz survival function provides a good description of the miracidial survivorship curves over the range of temperatures used, and we describe a maximum likelihood method of estimating the mean values of the parameters of this function, together with their approximate 95% confidence limits.