Abstract:Epinephelus fasciatus, a small grouper, is valued for its delectable flesh and substantial market value. This study utilized wild red grouper parents to examine artificial breeding, embryonic and post-embryonic development, and juvenile fish cultivation under industrialized conditions in northern China. At present, no documented studies exist on the artificial breeding, embryonic and post-embryonic development, and feed conversion processes of E. fasciatus under local factory conditions in China. This study focused on fertilized eggs and juvenile fish of E. fasciatus artificially bred in factories and recorded their embryonic development and instances of rapid growth. The study also explored the relationship between juvenile fish development and feed conversion, providing a scientific reference for the industrial breeding and aquaculture of E. fasciatus and its high-value utilization. The parent experiments, including fish cultivation, fertilization, and hatching, were conducted at Laizhou Mingbo Aquatic Products Co., Ltd. For egg collection, female red groupers with stage Ⅳ gonad development were selected for artificial induction. The oxytocin used was a mixture of HCG and LHRH-A3, which was administered at dosages of 350 IU/kg and 20 μg/kg of fish weight, respectively. Two days before sperm collection, a halved mixture was injected into mature male fish to promote sperm production. To obtain fertilized eggs, mature eggs were first collected in a dry plastic basin by compressing the abdomen, while sperm with high microscopic vitality were simultaneously collected for artificial insemination. Dry insemination was performed at a sperm-to-egg volume ratio of 1:500. After stirring, the eggs were allowed to stand for 5 min. The eggs were then washed with an equal volume of seawater and allowed to stand for 5 min. The floating eggs were collected and incubated in an incubation bucket with seawater maintained at a water temperature of (23.4±0.8) ℃, dissolved oxygen levels greater than 6 mg/L, and a salinity range of 28–30. Upon completion of the embryonic hole closure period, the eggs were collected with gauze and immediately transferred to a breeding pool with an egg-laying volume of 2–3 mL/m3 . Starting with fertilized eggs, 10 floating eggs were regularly removed from the hatching bucket, and an optical microscope (Nikon E200) was used to observe the embryonic development process. Photos were captured, and the time and developmental characteristics of each developmental stage were recorded. The time point of each developmental stage was defined when two-thirds of the embryos reached this stage. The fertilized eggs completed embryonic development within 31 h and 12 min under water temperature and salinity conditions of (23.4±0.8) ℃ and 28–30, respectively. Starting with the initial hatching of fry, fish fry exhibiting good growth from the breeding pool were regularly selected. A microscope (Nikon E200), dissecting microscope (Olympus), and Image View software were used to capture photos, measure total length, and record the developmental stages and characteristics of the fry and juveniles. During this period, samples were collected daily from 0 to 10 days post-hatching (dph), every 2 days from 10 dph to 20 dph, and every 5 days from 20 dph to 40 dph. Fish fry (3–5) was randomly selected at each time point to measure their total length and record their growth status. One-way ANOVA was performed on growth data using SPSS 27.0, with significant differences between groups compared using the least significant difference (LSD) and Duncan tests. Origin Pro 2022 software was employed for figure creation. The post-embryonic developmental sequences were divided into the early larval (0–3 dph), late larval (4–29 dph), juvenile (30–54 dph), and young (>55 dph) stages. At 3 dph, the larvae were fed S-grade rotifers. At 9–20 dph, L-grade rotifers were provided. At 20–30 dph, brine shrimp larvae were provided. Starting at 31 dph, the fish larvae transitioned from animal-based feed to compound feed. Compared to the early developmental stage, the growth rate, phenotype, scales, and body color of the larvae rapidly increased after transitioning to compound feed. This indicated a high acceptance of compound feed during the transitioning stage. The feeding frequency was twice daily, occurring at 08:00 and 16:00. The dimensions of the cultivation tank were 6 m × 8 m× 2.5 m, with a water flow exchange rate of 8 m3 /h. Dissolved oxygen levels exceeded 6 mg/L, salinity ranged from 28 to 30, and water temperature varied between 25 ℃ and 28 ℃. At present, although red groupers can be artificially reproduced, cultivation technology remains imperfect, and large-scale breeding has not yet been realized. This study systematically investigated embryonic developmental processes and early morphological changes in red grouper larvae produced using artificial insemination under industrial conditions. The early developmental patterns of metamorphosis, growth, and early body color changes were systematically documented, providing a reference for the artificial cultivation and scientific feeding of early fry and juveniles to mitigate mortality risk.
