During the period of WWII, fisheries continued in Japan. This is to secure food.

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But the oil that powers the ship's engine is the military's most important resource. Oil distribution is gone and large fishing vessels have been diverted to military transport vessels. Therefore, there was a limit to the ability to continue fishing. The fishermen used boats to row, but in addition to being able to fish only in the coastal areas, young fishermen were recruited by the Navy, resulting in a large drop in catch. Compared to 1939, the catch in 1945 fell to one-fifth. (63,753 tons → 12,951 tons)

At the end of the war, the fishing industry itself was no longer possible due to the effects of bombing and mines.

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It also had problems with domestic distribution. In 1942, from the perspective of food management, the government set a maximum price for each fish species. This effectively led to free work for fishermen. This period is called the "collapse period" in Japanese fisheries.

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References:

A Survey of Japan's Fisheries in War (1941-1945), Kansai University, etc.