An ayu is a species of fish that is the only member of the Plecoglossidae family. It is found in lakes and rivers as well as coastal regions throughout Japan, China and Taiwan. The ayu is sometimes known as the sweetfish due to its sweet tasting flesh. Its diet consists largely of algae and small animals including insects and worms. Due to its popularity as a food source the fish is farmed in large numbers for commercial reasons and is a highly sought after fish.
The ayu is an amphidromous fish, which means that it lives in both salt and fresh water regions and migrates between the two. In this case the fish moves between salt and fresh water during its lifetime but doesn’t do so to breed. This is why the fish can commonly be found in lakes as well as coastal regions. Typically, the fish will only live a single year and hence it is also known as the year fish. There are some ayu fish, however, which survive for longer than this.
The fish is native to the Palearctic zone, which is one of the eight zones of the Earth. This zone is the largest of these eight and includes certain regions of Europe and Asia including the Himalayas. Along with these regions the fish is also found in more southern areas such as the Korean Peninsula and Taiwan. During spawning season, which occurs during the spring, adult fish travel from coastal regions up into rivers. The larvae which are spawned during this time then travel straight back to the sea before the cycle begins again.
Ayu fish are omnivores, which means they eat both plants and other animals. Due to the small size of the fish it mostly feeds on small insects as well as water sponges. The plant food eaten by the fish mainly consists of algae. Algae includes a range of different species of underwater plants including seaweed and sea sponges.
In Eastern Asia the ayu fish is a popular dish due to its sweet tasting flesh. Although the fish are farmed in large quantities they are also caught by local fishermen and women who use techniques such as fly fishing and trapping. Some anglers in Japan also use cormorant fishing to catch ayu — a technique using a cormorant bird which catches the fish and then stores it in its beak before giving it to the fisherman.