Hatching process and the free embryonic stages in Notopterus notopterus. (a) Stage 24: just hatched-embryo after breaking the weak egg envelope, caudal part is relieved, anterior part still stuck in the remnant of the egg-envelope, note the emergence of dorsal and caudal fin anlage; yolk sac (yc) still covered with egg envelope, 168h:05min; (b) Stage 25: rupture the complete egg-envelope and free anterior part of the embryo, 168h:25min; note the tiny pectoral fin bud (black arrowhead); (c) Stage 26: jaw and branchial arches formed, day 8; (d) Stage 27: mouth opening, day 10; note the emergence of the swim bladder vesicle (sb); white arrowheads point to gradual development of dorsal fin. Scale bar = 5 mm.