Oxygen inhibits--even though in traces--the hatching of the eggs of the liver fluke Dicrocoelium dendriticum R.

A chamber was constructed to investigate the influence of gaseous surroundings on the hatching of Dicrocoelium eggs (Fig. 1). It was found that the exclusion of even traces of oxygen is the prerequisite for successful hatching. Oxygen was removed by baker's yeast suspensions as well as by dithionite solutions. Hatching rates reached a maximum when the carbon dioxide content of the chamber ranged between 0.1% and 4%. Under natural hatching conditions within the intestine of the pulmonate intermediate hosts, bacteria ensure oxygen consumption and carbon dioxide production. The consequence is the hatching of Dicrocoelium eggs. Carbon monoxide also stimulates hatching in the presence of oxygen and therefore seems to block the inhibition mechanism, which is based on oxygen acting. The hatching of eggs started about 5 min after exposure to hatching conditions and continued over a period of 60-90 min.