Study on Embryonic Development and Growth Characteristics of Epinephelus tukula

Our current understanding of the early developmental characteristics and growth traits of the potato grouper (Epinephelus tukula) is limited but necessary for the development of large-scale aquaculture farming of this species. To investigate this, this study used artificially propagated E. tukula and systematically observed embryonic and morphological development processes of both larvae and juvenile fish and analyzed the growth characteristics during the young developmental stage. Under water temperature and salinity conditions of 23.9 ± 0.4°C and 28-30 ppt, respectively, the fertilized eggs completed embryonic development in 25 h 34 min, sequentially passing through seven typical stages: fertilization, cleavage, blastula, gastrula, neurula, organogenesis, and hatching. The newly hatched larvae had an average total length of 1.60 ± 0.17 mm. The yolk sac and oil globule were visible at 1 dph (days post-hatching); at 3 dph they began exogenous feeding; the prototype of the “trident” appeared at 9 dph; by 30 dph, the fins were almost fully developed and the fish entered the juvenile stage; by 35 dph, the second dorsal fin spine and pelvic fin spine began to shrink; by 55 dph, spots and scales covered the entire body, and the fish entered the young developmental stage. After 105 dph, average body weight increased from 34.134 ± 5.85 g to 135.28 ± 20.11 g, and average total length increased from 13.41 ± 0.81 cm to 21.29 ± 1.15 cm. The best-fit model between average total length (TL) and age was the quadratic function TL = -0.001t² + 0.283t - 11.018 (R² = 0.982). The results of this study showed that the E. tukula has a relatively fast embryonic development rate, typical morphological changes in larval and juvenile stages, and rapid early growth in the young developmental stage, while the specific growth rate decreased with prolonged culture time. This study provides relevant biological information for the artificial propagation, fry rearing, and selective breeding of this species.