International Journal of Marine Science, 2025, Vol.15, No.5, 277-286 http://www.aquapublisher.com/index.php/ijms 278 2 Biological and Ecological Characteristics of Mackerel 2.1 Species distribution and ecological niche in Hainan sea area The mackerels in Hainan waters are mainly composed of S. commerson and S. guttatus. They are widely distributed in tropical to subtropical offshore waters and are ocean-migrating upper fish. Mackerel has the habit of swimming at high speed and eating fiercely. It occupies a high trophic level of marine food networks and plays an important role in maintaining the balance of offshore ecosystems. In the coastal coast of Hainan, mackerels migrate significantly in season. Every spring, when the coastal water temperature rises, the spawning group migrates to the coastal coast and completes spawning and breeding in coastal waters; then the adult fish migrate to the sea with abundant bait foraging, and may move to deeper seas for winter in winter. Analysis of trace elements of otoliths shows that blue-point mackerels migrate for long distances between spawning grounds, bait yards and wintering grounds, and their life history experiences are significantly different (Pan et al., 2020; Sougueh et al., 2023). Similar migration patterns are expected for mackerels in Hainan, allowing them to make full use of resources in different seas, but also means that environmental changes may have a greater impact on their reproduction and growth (Weng et al., 2020). 2.2 Life history characteristics and growth patterns Mackerel grows rapidly and has a relatively short life cycle. Studies have shown that narrow-band mackerel can grow to about 60 cm~80 cm at one in one age, and the total length can reach more than 100 cm within two years, and then the growth rate gradually slows down. Most mackerels mature sexually at 1.5~2 years old and are multi-spawning fish. They lay eggs in batches from spring to early summer every year. The absolute reproductive power of single female fish increases significantly with the individual size (Weng et al., 2020). A survey of blue-point mackerel breeding populations in the Yellow and Bohai Seas shows that dominant body recombination is concentrated in 0.5 kg~1.0 kg, accounting for 52% of the population. Rapid growth and early maturity are beneficial for population replenishment, but also make it more sensitive to fishing pressures (Mackie et al., 2005). 2.3 Economic and ecological value in marine ecosystems As an important economic fish, mackerel also plays the role of a "medium predator" in marine ecosystems, controlling small and medium-sized fish and cephalopod populations, thereby affecting the structure of the food web. Mackerel has extremely high economic value and is popular among consumers for its delicate meat and little thorns. Especially in Hainan, mackerel is expensive and is one of the "best fish" and has contributed significantly to the increase in income of local fishermen. In short, mackerel has both ecological and economic value, and its resource management and breeding of good varieties are crucial to the sustainable development of fisheries (Roa-Ureta et al., 2019). 3 Seawater Fish Selection and Breeding Strategies 3.1 Basic principles and methods of selective breeding Selective breeding is a traditional method of achieving genetic improvement of germplasm through targeted selection of individuals with excellent phenotypic traits. Among aquatic animals, breeding is used to achieve genetic improvement of quantitative traits such as growth, disease resistance, and meat through population selection and family selection (Kashyap et al., 2024). Compared with terrestrial animals, fish domestication and artificial breeding history have been shorter, but practice has proven that many farmed fish have made significant progress through selective breeding. In China, traditional aquatic genetic breeding is mainly concentrated in the field of freshwater fish, and the breeding potential of seawater fish is also huge. Fish have high reproductive power and large population size, and can build large-scale breeding groups in a short period of time, achieving high selection intensity and significant selection response (Janssen et al., 2017). However, seawater fish breeding also faces problems such as long generation cycles, high breeding facilities requirements, and inbred risks, and requires scientific breeding plans and long-term and stable investment. 3.2 Breeding practices in seawater fish In the breeding practice of seawater fish, group breeding and family breeding are common strategies. Group
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