Ziyu refers to mullet. In Compendium of Materia Medica written by Li Shizhen, it is recorded that "Mullet is black in color, hence its name, and Cantonese people mistakenly call it Ziyu". Mullet, also known as mullet, mullet, aconite, Qingtouzai, Qimouzai, Xinwu, Zhengwu, Jiugan, etc., is similar in appearance to barracuda, and its meat is tender and delicious, so it is known as "the most precious fresh food in Fujian".

mullet is a high-quality economic fish in the shallow water of warm zone, which is widely distributed in the Atlantic Ocean, Indian Ocean and Pacific Ocean. It is generally 2-4 cm long, with a cylindrical front, round scales all over the body, big eyes, fine fluffy teeth, born on the edge of the upper and lower jaws, deeply forked tail fin, bluish-gray body, back and head, and white abdomen.

mullet is a marine fish, which likes to inhabit at the entrance of rivers mixed with fresh water in Yu Xian, and some of them can be traced back to the pure fresh water river. The fishing season is from October to December of the following year.

mullet is tender in meat, delicious in taste, rich in nutrition, and without fine bones. Fish eggs can be made into caviar, especially mullet before the winter solstice, which is often regarded as a seafood dish in restaurants and is highly respected. It is recorded in Xie Zhaozhe's Five Miscellanies in the Ming Dynasty: "In the past, Fujian litchi, oyster house, roe fish and laver were the four beauties."