International Journal of Marine Science, 2025, Vol.15, No.2, 75-91 http://www.aquapublisher.com/index.php/ijms 79 questionable. Because the bones of Spanish mackerel lack obvious species characteristics, it is difficult to analyze its evolutionary history by traditional paleontology. Relatively speaking, the development of ancient DNA technology has provided new ideas for the study of paleogenetics of fish. If environmental DNA fragments of Spanish mackerels can be extracted from deep-sea sediments or polar ice cores, or DNA sequences can be detected from fish bones at medieval human sites, it is expected to compare differences in modern populations (Zeng et al., 2022). Paleoclimatic marine sediment indicators (such as organic matter markers) show that after the last ice age, productivity in tropical upwelling areas may have promoted the prosperity of middle and upper-class fish such as Spanish mackerel. In addition, some ethnic archaeological records indirectly reflect the changes in the distribution of Spanish mackerels in historical periods. For example, the emergence of narrow-band Spanish mackerels has been recorded in the eastern Mediterranean since the end of the 19th century, which is believed to be the result of migration to the north via the Suez Canal. This type of prehistoric/historical data combined with modern genetic diversity patterns can verify the reliability of molecular clock inference. 4 Ecological Adaptation Mechanism of Spanish mackerel 4.1 Evolution of temperature and salinity tolerance As a large-scale migratory fish spread throughout the temperate to tropical areas, Spanish mackerel has formed a widespread adaptation to environmental factors in its long-term evolution. The first is tolerate and adapt to water temperature. Most species of the genus Spanish mackerel prefer warm waters, and the temperature range is generally between 18 ℃and 30 ℃, but the tolerance of different species to low temperatures has evolved. The northernmost Japanese Spanish mackerel can tolerate seawater temperatures as low as about 10 °C in winter, so it can overwinter in the Yellow Sea and Bohai Seas (Harada et al., 2021). On the contrary, some strictly tropical species such as Borneo mackerel (S. multiradiatus) retreated to the waters near the equator when the water temperature dropped slightly. This difference stems from the differences in population selection and metabolic regulation capabilities of cold adaptive genes. Studies have found that Japanese Spanish mackerel can maintain body function by increasing basal metabolic rate and heat production at low temperatures, while tropical species lack this mechanism. In terms of salinity, Spanish mackerels usually live in normal salinity seawater offshore (about 30‰~35‰), but can tolerate a certain range of salinity fluctuations. For example, in the estuary area, Spanish mackerels in the juvenile stage can enter mixed waters with slightly lower salinity for feeding. Its gills and kidneys have good osmotic regulation functions and can cope with the impact of salinity changes on fluid balance. These physiological adaptation features allow Spanish mackerels to utilize extensive nearshore niches (Eaton et al., 2024), distributed from the tropical coral sea to the temperate continental shelf. In recent years, environmental DNA and transcriptomic studies have further revealed the molecular basis of Spanish mackerel's adaptation to warm salt. Some cold-resistant populations show high expression of anti-cold-related genes (such as anti-freeze protein genes), while high-temperature-resistant populations have heat shock proteins used to deal with heat stress. These evolutionary adaptations make Spanish mackerel a "versatile" in dealing with changing marine environments, and its distribution adjustment ability is also relatively strong in the context of global climate change. 4.2 Efficient predation and migration ability Spanish mackerel is a typical middle and upper-class swimming predator, and has evolved a series of morphological and physiological characteristics that are conducive to predation and migration. First, its streamlined body, high proportions of white muscles and developed tail shanks are conducive to rapid swimming, with burst speeds exceeding 10 meters per second, which allows it to quickly chase prey and migrate long distances. The tail fin of the Spanish mackerel is crescent-shaped, and the fork tail helps reduce drag and generates strong thrust. Coupled with the tiny round scales on the surface and the skin recessed structure, it can reduce turbulence, making it an ideal design for high-speed swimming. Secondly, Spanish mackerel has sharp teeth and strong jaw muscles, and is good at preying on middle and upper fish schools, such as sardines, anchovies, mullets, etc. They often hunt in groups, forcing the prey fish to the water and rushing hard to bite, and feeding efficiently. In an uneven distribution of food resources in the marine environment, Spanish mackerels rely on rapid movement to search for bait and capture it, and their digestive tracts are short to quickly process
RkJQdWJsaXNoZXIy MjQ4ODYzNA==