* Japanese name: Ayu
* Scientific name: Plecoglossus altivelis altivelis
* Description: Ayu are as Japanese as cherry blossom. Small fish in the salmon family, they grow to about 20 cm long, sometimes reaching 30 cm. Ayu are celebrated as being, when skewered and grilled over a fire, one of the tastiest of all river fish. Just the word “ayu” will evoke wistful thoughts of summer in many Japanese.
* Where to find them: In fast-flowing rivers from western Hokkaido south through Kyushu. Ayu, the most important species in Japanese freshwater fisheries, can be credited with stimulating a growing environmental awareness in Japan, as — to the chagrin of many — suitable habitats for them have been disappearing as a result of rampant dam-building across the country.
* Food: Most fish in the salmon family are strictly carnivorous, but ayu feed mainly on water weeds. The fish scrape the algae from rocks, and teeth marks can be seen on rocks where ayu have eaten. Juvenile fish also take aquatic insects.
* Special features: Ayu are highly territorial when it comes to their feeding grounds. Each fish defends a fairly large area of 10 to 20 sq. meters, and will attack any fish entering the territory. It is this predictable defensive behavior that anglers all over Japan exploit in order to catch ayu. A live ayu is introduced on a hook into another fish’s territory. When the territorial fish attacks the intruder, it too is caught. In March, adults swim down river to spawn. Larvae enter the ocean and feed on plankton there over the winter, returning to rivers in the spring. Some fish survive to spawn for two or three years in succession; others manage to do it only once. Scientists have succeeded in making transgenic ayu, that is, ayu that carry a gene from another species. Ayu DNA was supplemented with a gene from a rainbow trout. The gene produces a growth hormone, and as a result the transgenic ayu grows to be twice as heavy and 1.3 times as long as normal ayu. The survival rate of the transgenic animals is, however, not as high as for normal fish. The scientific paper reporting this did not give details about how delicious the transgenic fish were.

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