Rapid hatching of mechanically-disturbed eggs of the monogenean gill parasite Diclidophora luscae, with observations on sedimentation of egg bundles

Abstract

The polyopisthocotylean monogenean, Diclidophora luscae, from the gills of the pouting, Trisopterus luscus caught off Plymouth, England, lays its eggs in bundles. When the eggs in the bundles contain fully developed larvae, rapid hatching is stimulated by mechanical disturbance and oncomiracidia begin to emerge within 10s after the start of agitation. Larvae continue to hatch for 5 min after the end of agitation. Hatching occurs when eggs are mechanically disturbed either during light or darkness (LD 12:12). No evidence was found that shadowing has a stimulatory effect on hatching. The production of egg bundles, which sink more rapidly than isolated eggs, and the presence of egg appendages resembling grappling hooks, may be adaptations to reduce the chances of the eggs being swept away from areas inhabited by the bottom-dwelling host. The latter feeds on benthic organisms and its activities might provide mechanical stimuli sufficiently strong to stimulate hatching of D. luscae eggs.