International Journal of Marine Science, 2025, Vol.15, No.5, 277-286 http://www.aquapublisher.com/index.php/ijms 280 and reproduce under artificial conditions. Mackerels are lively and frightened by nature. They require special water conditions and sedation measures when induced by broods and artificial egg collection (Chiu et al., 2025). 4.3 The influence of Hainan water environmental factors on the growth of mackerel In this study, we successfully obtained sufficient fertilized eggs for family construction by simulating natural light temperature cycles in parent fish ponds and reducing artificial interference. These regional factors have had an impact on the formulation of breeding programs. We chose to cultivate family lines in spring and summer based on the environmental characteristics of Hainan waters, and adopted a scattered and multi-point cage breeding method to reduce weather risks. The research area was selected in the deep-water cage breeding area along the eastern coast of Hainan. The water quality in this sea area is clear, the flow rate is moderate, and the bait is rich, which provides ideal conditions for the growth of mackerels and ensures the consistency of the environment during breeding experiments (Figure 1) (Chen et al., 2021). Figure 1 Seasonal mean observed catch rates of S. commerson caught using trammel nets in the WT (Adopted from Chen et al., 2021) 5 Genetic Variation of Growth Traits 5.1 Heritability estimation of major growth traits Before conducting genetic assessment, the heritability level of the main growth traits of mackerel was first determined. Heritability reflects the proportion of trait phenotypic variation explained by genetic factors and is a basic indicator of selection and breeding of aquatic animals. This study was based on a semi-compatriot family model and heritability estimates were performed on the body length, weight and growth rate of a mackerel fish. The results showed that there was a moderate degree of variation in heritability of different growth traits. Among them, the estimated heredity value of body weight is about 0.3, which is a moderate heredity; the heredity of body length is slightly lower, about 0.15~0.2. This is consistent with the research results of other seawater fishes. For example, the weight heritability of red-fin oriental horns is 0.36 and the body length is 0.14, both of which are within the medium or low heritability range. The moderate level of heritability indicates that the growth traits of mackerel are significantly affected by genetic factors, and better improvement effects are expected through selection breeding. Heritability is not static and may change with the development stage of the fish body. Studies have found that the growth traits in the juvenile Nile tilapia have a higher heritability and decreases with increasing age (He et al., 2018). This may be due to the increased effect of environmental factors in the later stage, or the narrowing of genetic differences between individuals after growth enters the inflection point. In mackerels, we also observed a similar trend, with higher heritability estimates for body length and weight in young age (within 6 months of age), while lower heritability before and after sexual maturity (12~18 months of age) (El-Nady and Obeida, 2000).
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