Objective Carry outing fully industrialized indoor breeding of Plectropomus leopardus, and investigating the characteristics and patterns of embryo and early post embryonic development of P. leopardus in the north indoor factory workshops.

Methods  This study used microscopic imaging and morphological measurement observation methods to track the early developmental processes and characteristics of fertilized eggs of P. leopardus obtained through indoor factory cultivation and natural reproduction.

Results  we found the zygotes were transparent floating spherical eggs with an average diameter of (887.08±10.28) μm and a single oil bulb with an average diameter of (166.60±10.81) μm. Embryonic development experience 8 classical development stages, including fertilized egg stage, blastodisc stage, cleavage stage, blastula stage, gastrula stage, neurula stage, organo-forming stage, hatching stage and etc, subsequently divided into 27 stages. The fertilized eggs were hatched out at 27 h 13 min after fertilization followed by the larval stage. The total length of the hatched out larvae was (2.156±0.281) mm. According to the absorption of yolk sac, larval stage was further divided into pre-larval stage (0-3 (days post hatching, dph), not complete absorption of yolk sac) and post-larval stage (4-30 dph, complete absorption of yolk sac). The oil globule disappeared at 4 dph and the swimming bladder appeared at 8 dph. 28 days after hatching, the total length (15.32±1.98) mm, the length of the second dorsal fin spine (8.04±1.06) mm, and the length of the first pelvic fin (5.97±1.37) mm, extended to the maximum value. Afterwards, the length began to shorten. When the dorsal fin spine contracted to the minimum value (3.26±1.13) mm, all kind of fins began to complete, scales began to appear and body color began to deepen, marking the entry into the juvenile stage. At 71 dph, entering the adult fish, the total length (40.21±1.33) mm, the body shape was similar to that of the adult fish and the whole body was covered with scales and baby blue spots.

Conclusion  For the first time, this study achieved the natural reproduction spawn and artificial cultivation of P. leopardus in the northern industrial workshop, revealing its early growth and development characteristics and pattern,laying a theoretical and technical basis for the the full factory batch cultivation of leopard coral grouper seedlings.