Fig. 1. Photomicrographs of oocytes and eggs observed in biopsies taken from Atlantic halibut, including a water-hardened egg following its incubation in sea water. The inset (below) shows three stages of hydrating oocytes in a typical biopsy. Oocytes are partially dissected and spread out in FO medium for clarity. Oogonia (black arrows on the biopsy plate), were clear, round orbs lacking yolk platelets (mean diameter 0.21±0.08 mm). The pre-hydrated oocytes (1) appeared dark in the biopsy under transmitted light due to diffraction and scattering caused by the yolk platelets. Hydrating oocytes (2) showed increased transparency with increased size, as a result of yolk platelet coalescence. The ovulated eggs (3) were fully separated from their follicular layers, and were highly transparent. The water-hardened egg shows the newly formed perivitelline space (PVS) and blastodisc resulting from cytoplasmic streaming to the animal pole upon water activation. The eggs were not fertilised.