Observation on embryonic development of cage-breeding Siganus oramin

The parent fish of Siganus oramin were bred in deep-sea anti-wave cage. We selected the 1⁺ aged parent fish with mature sex glands for spawning artificially and dry insehation. The fertilized eggs obtained were incubated in laboratory for observation of the whole process of embryo development. The results show that the ovulation and insemination behavior of cage-breeding S.oramin still remained a strict rhythm of the calendar after being induced spawning in a cement pool. The mature zygote of S.oramin was heavy, sticky and round with multi-oil ball, and the egg membrane was smooth and ooplasm transparent. The diameter of zygote was (584.6±8.64) μm, and the maximum oil ball diameter was (146.54±7.46) μm. The first larvae hatch finished at 39^th hour 20 min under 23.2–24.5 ℃ at salinity 32.5 and pH 8.2. All fertilized eggs completed incubation at 42^nd h 10 min with accumulated temperature of 925.28–996.45 ℃·h. According to morphological characteristics, the process of embryonic development could be divided into seven physiological stages with 26 periods: blastoderm form stage, cleavage stage, blastula stage, gastrula stage, neural stage, organogenesis stage and hatching stage. The body length of newly hatched larvae was (1 912.54±105.25) μm; the larvae opened mouth at 2.5 dph (56 h after incubation) with total length of (3 030.36±80.97) μm.