This study attempts to observe and record early embryonic developments of the orange mud crab,Scylla olivacea. The period taken by the eggs to hatch was 8 days and the colour of the eggs gradually changed from yellow to brown, gray and dark gray. During the embryonic development, the developing embryos reached the blastula stage within 24 hours with a mean egg diameter of 329.91±6.62 µm. The embryo developed into the gastrula stage on the 2nd day with a mean egg diameter of 337.10±8.37 µm. Eyes were consequently observed on the 3rd day and there was a further increase in the yolk-free portion with a mean egg diameter of 338.16±6.57 µm. On the 4th day, the eye-spot became crescent and there was a clearer tissue formation with a mean egg diameter of 358.45±14.80 µm. Meanwhile, on the 7th day prior hatching, there were many chromatophores present, mostly dark in colour and the yolk granules had further reduced in size. The heart beats faster than previous days before and the embryo occupied most of the available egg volume with a mean egg diameter of 377.26±11.50 µm.

Keywords: Aquaculture, Crustacean, Embryonic development, Mud crab,Scylla olivacea.