The effects of light intensity on hatching of Echinostoma caproni Miracidia

Egg cultures of Echinostoma caproni were exposed to 25-W incandescent light at control intensities (9.7 mumol s-1 m-2) and reduced intensities (1.0, 0.5, 0.25, 0.125, 0.06, 0.03, and 0.01 mumol s-1 m-2). Low intensities of light did not affect the diurnal hatching rhythm of the miracidia, with maximum hatching occurring from 1200 to 1300 hr. However, at 0.5, 0.25, and 0.125 mumol s-1 m-2, hatching was delayed 2 days at each interval. From 0.06 to 0.01 mumol s-1 m-2, hatching still occurred, but at 17 days of development rather than at the 11.3-day average found under illumination with a 25-W incandescent light. No appreciable hatching was observed in cultures kept in the dark.