Egg development, hatching and early life-history of Dissonus manteri (Copepoda), parasitic on the gills of coral trout, Plectropomus leopardus.

The early life-history of Dissonus manteri differs markedly from that of Caligidae and from that of its congener Dissonus nudiventris. The uniseriate egg strings are of typical caligid form, but the stage hatching from the egg is a preecdysis nauplius which moults immediately to the copepodid. The empty naupliar cuticle remains tethered to the egg string by a pair of posterior threads which attach to the internal surface of the egg membrane. The duration of egg development is 112 h and the mean duration of hatching is 5.2 h at 25 degrees C. Aeration and water movement are important for successful hatching. Under these conditions, hatching success is 94.8%, but decreases to 48.4% in static water with no aeration. Mean survival time of the copepodid in the absence of a host is 41.4 h at 25 degrees C. The reduction of early free-living stages in the life-cycle and the high survival rate from egg to copepodid could be important in future coral trout aquaculture, since the potential for re-infection by this parasite is very high.