Why are large mackerel available in winter?

1. Energy Storage and Fat Content (The Main Reason)

A. Frenzied Feeding in Summer: Summer is the peak season for marine productivity (plankton). Mackerel feed heavily in cold northern waters (such as northern Japan and the Russian Far East), growing rapidly and actively storing fat subcutaneously and in their muscles.

B. Winter Migration and "Fattening": As water temperatures drop in autumn, mackerel schools begin their southward migration in search of suitable temperatures. By the time they reach the Japanese coast, they have accumulated extremely high fat content (sometimes exceeding 20%). At this time, the mackerel are plump and have full flesh, making them the highest grade.

C. The Significance of Fat: High fat content not only means larger size and a richer flavor, but it is also a survival strategy for them to survive the relatively scarce food winter and store energy for spawning in spring.

2. Spawning Cycle and Changes in Flesh Quality

A. Before and After Spawning: Mackerel spawn primarily in spring. Winter is their "preparation period" before spawning, and the development of their gonads requires a large amount of nutrition, further promoting the fish's plumpness.

B. Post-spawning weakness: After spawning in spring, mackerel experience significant energy expenditure, becoming thin and weak, with a sharp drop in fat content, resulting in loose flesh and a bland taste.

3. Water temperature and metabolism

A. Low winter temperatures: Cold water environments slow down the fish's metabolic rate. This helps mackerel retain accumulated fat, preventing it from being burned off too quickly. At the same time, the low seawater also makes the flesh firmer.

B. High summer temperatures: Although they eat more in summer, their metabolism is also faster, with more energy used for rapid growth and daily activities. The "net accumulation" efficiency of fat may not be as high as during the autumn to winter period.