The effects of environmental factors on the development, behaviour and survival of Paramphistomum microbothrium miracidia.

The effects of temperature, hydrogen ion concentration, salts, light, gravity and living organisms on the development, survival and behaviour of Paramphistomum microbothrium miracidia were studied. Isotonic water environment of pH 7-8 and temperature of 25 degrees C were found to be most favourable for miracidial development and hatching. Miracidia longevity was highest at 21 degrees C in an isotonic water environment of pH 6-8. Demineralized water reduced the longevity of miracidia. Miracidia exhibit a strong phototaxis and a weak geotaxis, the latter being manifested only in the absence of light, and they show a preference for a medium with a low Ca/Mg ratio. An unidentified fungus, probably of the group of Fungi Imperfecti, had a deleterious effect on egg development. Aquatic organisms such as molluscans, dipterans and amphibia affect the survival of the miracidia. The relationship between observed phenomena and dynamics of infection are discussed.