Crustaceans like lobsters have a higher proportion of glycogen, a polysaccharide that converts into the simple sugar glucose. Glycogen is aptly named: It is derived from the Greek words glukus (sweet) and gen (a suffix meaning "capable of bringing forth"). Other substances, including the amino acid glycine, influence sweetness intensity too.
Among the three most widely eaten crustaceans, lobster is the sweetest, followed by crab and shrimp in that order. Fish flesh, though less sweet than crustacean meat, is sweeter than land animals muscles. Whatever the flesh, sweetness starts to diminish noticeably after a day or two of storage time.
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