鲜鱼 (xiānyú) means fresh fish, combining 鲜 (fresh) and 鱼 (fish). It refers to fish that has been recently caught and not preserved, frozen, or processed.
这家餐厅每天都用鲜鱼做菜。
Zhè jiā cāntīng měitiān dōu yòng xiānyú zuòcài.
This restaurant uses fresh fish to cook every day.
早市上的鲜鱼又便宜又新鲜。
Zǎoshì shàng de xiānyú yòu piányi yòu xīnxiān.
The fresh fish at the morning market is both cheap and fresh.
妈妈买了一条鲜鱼,打算晚上做汤。
Māma mǎi le yī tiáo xiānyú, dǎsuàn wǎnshang zuò tāng.
Mom bought a fresh fish and plans to make soup tonight.