The logic is simple. Fish, especially sushi, should be served as fresh as possible and not many fishermen catch fish on a Sunday - or Saturday, or Friday for that matter - which is why it's widely speculated that the fish you buy on a Monday can often be four or five days old.

The "no seafood on Monday" rule was famously popularized by chef Anthony Bourdain in his 2000 book Kitchen Confidential. The logic was that most fish markets were closed on weekends, meaning the fish served on Monday was likely caught on Thursday or Friday and had been sitting in a walk-in cooler for three or four days. However, in 2026, this is largely a culinary myth for high-end or coastal restaurants. Modern global logistics, overnight shipping, and 7-day-a-week fish auctions mean fresh catch can arrive on Sunday night or Monday morning. That said, in smaller towns or landlocked areas, the rule can still hold some weight as a caution against "weekend leftovers." Most sushi restaurants and seafood specialists now pride themselves on daily deliveries, making Monday just as safe as any other day for a high-quality fish dish.