International Journal of Marine Science, 2025, Vol.15, No.5, 277-286 http://www.aquapublisher.com/index.php/ijms 279 breeding (also known as large group individual selection) is the choice of individuals with the best phenotype from each generation as parents. Its advantages are simple operation and short-term effectiveness, and are suitable for species with high reproductive power. Family selection and breeding can select excellent families by establishing multiple artificial family lines and comparing the average phenotypic performance between family lines, which can improve selection accuracy and effectively control inbreeding (Tong et al., 2023). For marine aquaculture varieties, a series of successful breeding cases have been carried out at home and abroad. For example, Chinese scientific research institutions have selected and bred five generations of wild yellow croaker groups to cultivate a new "Big Yellow croaker East China Sea No. 1" product that is resistant to low temperatures and fast growth. The growth rate and survival rate of yellow croaker in the breeding group were significantly higher than that in the control group, and the production performance advantages were obvious (Zhao et al., 2021; Ding et al., 2024). Experience shows that scientifically designed breeding programs can make full use of genetic variation and achieve effective improvement of seawater fish traits. 3.3 Learning from other species In emerging breeding objects such as mackerel, we can learn from the successful experience of other species, gradually establish basic groups, measure genetic parameters, and implement continuous breeding. Excessive incommendation should be avoided during the selection process to prevent loss of population genetic diversity and inbred decline (Kobayashi et al., 2025). At the same time, breeding goals should coordinate multiple traits to avoid adverse responses related to traits by focusing only on a single indicator. For example, while improving growth rate, taking into account disease resistance and environmental adaptability, we can cultivate new varieties of seawater fish with excellent production performance and adaptability. 4 Case Background and Study Area Overview 4.1 Current status of Hainan offshore fishery resources Hainan Province is located in the tropical region and has a coastline of 1 500 kilometers. The water temperature in the offshore waters is between 23 ℃ and 30 ℃ all year round, and fishery resources are very rich. In recent years, Hainan has actively built a modern fishery system, and emerging models such as deep-water cage farming have developed rapidly, and the output value of marine fishery in the province has continued to grow. In 2024, the province's fishery output value increased by 11.2% year-on-year, of which the output value of seawater aquaculture increased by 13.0%. However, the traditional fishing fishery in Hainan's offshore has stabilized or even declined, and the sustainable supply of high-quality economic fish resources is under pressure. To this end, Hainan Province has vigorously developed the aquatic seed industry and made artificial breeding and seed supply of precious varieties such as mackerels as key tasks. Thanks to excellent water quality and technical research, Hainan has successfully broken through the key technologies of artificial breeding of mackerels and filled the gap in the domestic seedlings (Pan et al., 2020). At present, due to its fast growth and high value, mackerel has become one of the important varieties of deep-sea cage breeding along the southern coast of China. This regionalized aquaculture promotion provides basic groups and practical conditions for this study. 4.2 Regional characteristics of mackerel breeding and breeding Hainan mackerel breeding and breeding have significant regional characteristics. Hainan's sea area belongs to a tropical marine environment. The high temperature and high salt hydrological conditions prolong the growth period of mackerel, which is suitable for its rapid growth most of the year. However, high water temperature also means that when breeding, you need to pay attention to the heat resistance and low oxygen resistance of fish, and cultivate strains that are adapted to the extreme high temperatures in summer. Secondly, Hainan has abundant bait biological resources, and small middle and upper-level fish and crustaceans provide sufficient natural bait base for mackerels, which is conducive to their growth and development (Rajesh et al., 2017). However, extreme climate events such as monsoons and typhoons can cause significant fluctuations in the offshore environment, with phased effects on the feeding and growth of mackerels (Fardilah et al., 2024). Therefore, when conducting mackerel breeding experiments in Hainan, it is necessary to consider the interference of seasonal environmental factors on growth trait evaluation. Since mackerel is a predatory fish that swims at high speed, it is difficult to domesticate
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