Perhaps fishermen were catching mullet even earlier than that. They may not have known where the fish came from, but they knew that they arrived on time each year, and so they called them hsin yu, or "trusty fish."
也許更早的時候，漁民已在捕烏魚，他們雖然不知道烏魚從哪來，因為它年年準時到，就稱它為「信魚」。