Ayu is a unique and rare freshwater fish in the Nanxi River. It is 15 to 20 centimeters long and weighs about two to three liang to half a catty.

Nanxi River is rich in sweetfish and has long been famous. As early as the Wanli period of the Ming Dynasty, sweetfish were produced in Nanxi River. According to the "Wenzhou Prefecture Chronicles" written by Wanli of the Ming Dynasty, the sweetfish is "three to four inches long, has a good taste without any fishy smell, and is only available in clear water in October, which is slightly different from Lechan." "Yandang Mountain Chronicles" also records: "It can be found wherever the water flows. If the water flows westward to Yongnan River, it can also be found in Fenglin, Dangxi, Xiatan, and Ancient Temple Lake." Xiangyu. Commonly known as "brook carp", it is also called melon fish. It belongs to the order Salmoniformes and is named after the sweet fish. Ayu has a long body with flat sides, a small head and pointed snout, thin scales on the body, gray-black back and silvery white abdomen. The fish meat is tender and fatty, and tastes fresh and fragrant. It is a high-quality edible fish and a valuable economic fish. It is vegetarian. It is known as the "King of Freshwater Fish".

In addition to Nanxi River, sweetfish are also produced in southern Fujian, Taiwan and Xingshan County, Hubei. Legend has it that when Emperor Qianlong was touring the south of the Yangtze River, he tasted the flavor of sweet fish and praised it so much that he named it a tribute and paid tribute to the court every year. Ayu is also produced in Bitan, a tourist resort in Xindian River on the outskirts of Taipei, Taiwan. It is said that this kind of sweet fish in Taiwan was introduced from southern Fujian when Zheng Chenggong, the "national surname master", led his troops to drive out the Dutch invaders and develop Taiwan. Later generations remembered Zheng Chenggong and called the fish "the national surname fish". A poem by a poet in the Qing Dynasty said: "The spring water adds a new stream to the Xindian River. The stream is green under the glass. I catch ayu just three inches high. I fight for wine with two oranges and clouds listen to orioles."

Fishermen on both sides of the Nanxi River catch ayu. , usually riding bamboo rafts and driving cormorants to catch fish. A bamboo raft, seven or eight cormorants can catch more than 10 kilograms. "Cormorant eyes in the vast expanse of sand, water soaks into the blue sky without a trace. What they love most is that the reeds are wet after the rain, and a firework is used to cook the fishing boats." Lin Bu's poem in the Song Dynasty vividly depicts the interest of fishermen on the water. Sometimes guests from the farmhouse would come in the evening, and the host would carry a fish basket on his back and go down to the stream with a net bag. In a short time, he would pick up one or two pounds of fresh fish, which was as convenient as picking beans in the vegetable garden.

When making ayu dishes, it is better to stew and roast them. The peasant women on the banks of the Nanxi River have a good way of baking sweetfish. First, cut the back of the fish open, place it on a wire plaque or bamboo strips, and slowly smoke and bake it with fine smoke over a slow fire until it turns golden brown. Take it out. This is the sea fish. The famous dried sweet fish at home and abroad is such as when cooking noodles or making soup, break it into pieces and add some, and then sprinkle some onion medicine and minced ginger, the fragrance will be overflowing, and the color, aroma and taste will be good.

The poet Ren Shizhen of the Qing Dynasty wrote the poem "Qijue": "Nanxi River is full of fishermen, and the Liumoqingxi area is sparse. Fortunately, after the sun sets and the wind and rain, half of the river's mangroves sell sweet fish." Nanxi River in late autumn The arrival of sweetfish on the market has busy tourists visiting Nanxi River and owners of nearby restaurants, who all rush to buy fresh sweetfish. For example, under the paper windows of the tile-roofed house under the flowers and the moon, with rich village mash and steamed plate of sweet fish with unique flavor, "he drank with his neighbor and drank with his neighbor, and breathed his last breath through the fence", which was a unique pleasure.