Observation on the embryonic and post-embryonic developmental characteristics of blue round scad (Decapterus maruadsi)

Blue round scad (Decapterus maruadsi) is an economically significant fish species in China. Wild juveniles of D. maruadsi have been caught and are being cultured in net cages in China. However, the lack of artificial seedlings has limited the cultural scale of D. maruadsi in China. To date, there have been no reports on the propagation of D. maruadsi. To explore artificial breeding techniques for D. maruadsi, fertilized eggs were obtained by injecting HCG. The embryonic and post-embryonic development processes were observed and imaged using stereomicroscopy, and the characteristics of each stage from fertilized egg to juvenile fish were described. The results showed that D. maruadsi fertilized eggs were spherical, buoyant, and colorless, with an average diameter of (763.4±27.6) μm, containing a single oil globule. Under conditions of hatchery with temperature of 22.10–25.17 °C , salinity of 32.56–33.91, dissolved oxygen of 4.85–5.95 mg/L , and pH of 7.94–8.07, the fertilized eggs hatched in 19 hours and 10 minutes. The oil globule was completely absorbed at 48 hours, and the swimming bladder appeared at 72 hours. Embryonic development included 8 main stages, subdivided into 23 periods: fertilized egg, blastoderm, cleavage, blastula, gastrula, neurula, organogenesis, and hatching. Post-hatch development consisted of prelarval and larval stages. Newly hatched larvae had an average total length of (1 777.5±156.5) μm, with an average daily growth rate of 565 μm/d from 0 to 17 days post-hatching.