Because seafood when caught still retains a high amount of its original moisture, micro-organisms are quick to form on the fish. They in turn eat the amino acids, making them metabolize and producing a "fishy" smell.
凡事有利就有弊，海產往往夾著腥味，因為儲存環境濕度高，微生物生長快，豐富的蛋白質就成了它們的養料，胺基酸不斷分解代謝，腥味就出來了。