Animals

19 Ayu Fish Facts You'll Never Forget!

Discover fascinating ayu fish facts about its small body, feeding, young, and more!
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The ayu fish, scientifically known as Plecoglossus altivelis, is a fish species that is the sole member of the Plecoglossus genus and belongs to the Plecoglossidae family. It is also known as the ai or ayu sweetfish in Japan because of its flesh's sweet taste. It is a highly popular food in East Asia. This sweetfish (Plecoglossus altivelis) is a delicately flavored fish that is grilled and skewered over fire and is considered to be one of the most delicious river fish. It is indigenous to East Asia and occurs across the northwestern Pacific Ocean near the Hokkaido coast in Japan, and spreads southwards to China, the Korean Peninsula, Vietnam, and Hong Kong. It can be found inhabiting rivers that are very clean and fast-flowing. It is one of the most important fish species among Japanese freshwater fisheries. Increasing environmental awareness among Japanese people is helping this fish, as the habitats of this fish in Japan have been disappearing due to dam-building.

It is a fish species that is quite small in size and ranges between 6–12 in (15.2-30.4 cm) in length. The unique ayu sweetfish is olive or light yellow in color and is distinguishable from other fish due to its sail-like dorsal fin, teeth arrangement, and ridged tongue. It feeds upon water weeds, algae from rocks, crustaceans, sponges, worms, and aquatic insects. Their teeth marks can be spotted easily on the rocks they fed upon. Japanese fish of this species will attack any intruder and this behavior of the ayu sweetfish is exploited by some Japanese anglers who use this behavior to lure and catch the fish. This tends to work like a charm with the fish getting caught easily. This fish does not have a long lifespan, and adults might only live for two to three years. Adults swim down to the river in March to spawn. The larvae of the Plecoglossus altivelis enters the sea and preys upon plankton during the winter, and then in spring, it returns to the river. Keep reading to get to known more exciting facts about the unique ayu fish!

If you enjoyed reading our ayu fish facts, you must check out our bumphead parrotfish surprising facts and shortfin mako shark fun facts as well!

Ayu Fish

Fact File

What do they prey on?

Water weeds, algae from rocks, crustaceans, sponges, worms, and aquatic insects

What do they eat?

Omnivore

Average litter size?

Approximately 10,000 eggs

How much do they weigh?

0.01-0.82 lb (4.5-371.9 g)

How long are they?

6–12 in (15.2-30.4 cm)

How tall are they?

N/A

What do they look like?

Light yellow or olive-colored

Skin Type

Wet, slimy scales

What are their main threats?

Fishing, harvesting, dams and water management, and pollution

What is their conservation status?

Data Deficient

Where you'll find them

Marine and freshwater reserves like seas and rivers

Locations

The western Pacific Ocean, western Hokkaido in Japan, the Korean Peninsula, China, and Taiwan

Kingdom

Animalia

Class

Actinopterygii

Scientific Name

Plecoglossus altivelis

Family

Plecoglossidae

Genus

Plecoglossus

Ayu Fish Interesting Facts

What type of animal is an ayu fish?

The ayu fish, Plecoglossus altivelis, is a fish that belongs to the family Plecoglossidae and is the sole member of the Plecoglossus genus. Smelts are relatives of the ayu sweetfish as both of them belong to the same Osmeriformes order. The sweetfish (ayu or ai) is a marine animal that is eaten as food and has an exquisite taste when seasoned with sea salt. It is eaten commonly in the summer season, particularly in the Asian continent.

What class of animal does an ayu fish belong to?

Plecoglossus altivelis fish belong to the class Actinopterygii.

How many ayu fish are there in the world?

The population of this species has not been evaluated yet. However, we do know that their population trend is declining. The major threats that they face are fishing, harvesting, dams and water management, and pollution

Where does an ayu fish live?

This fish is indigenous to East Asia and can be seen across the northwestern Pacific Ocean near the Hokkaido coast in Japan. Its range spreads southwards to China, the Korean Peninsula, Vietnam, and Hong Kong. Some populations also reside in the lakes of Japan, like Lake Biwa. This species has also been introduced in Taiwan. It can be found inhabiting rivers that are fast-flowing. It is a migratory sea animal that migrates upstream in clear river waters in order to spawn.

What is an ayu fish's habitat?

The typical ayu fish habitat varies as it matures. It is an amphidromous creature that migrates to freshwater rivers and lakes with clean water from coastal marine waters after it matures. As Japanese streams are not of great depths, this species is found in shallow waters only.  

Who does the ayu fish live with?

It can be spotted swimming in small schools at the river mouth.

How long does an ayu fish live?

It lives for two to three years. In a river, they are likely to only survive up to one year but in a lake, they can survive for two to three years!

How do they reproduce?

Adults swim to the river in March (spring) to spawn. The larvae of this species swim to the ocean where they remain throughout winter and feed on plankton. They return in spring to the river. A few survive for two to three years and are able to spawn each year, while others spawn only once. When breeding this fish in captivity, scientists have successfully produced a transgenic ayu that carries a gene from a rainbow trout which helps the ayu to be two times heavier and live 1.3 times longer.

What is their conservation status?

The conservation status of the ayu has not been evaluated by the IUCN yet. It is officially listed as Data Deficient. This fish is threatened by fishing, harvesting, dams and water management, and pollution. The ayu is classified as threatened in Taiwan. Interestingly, these Japanese fish are extremely territorial and will attack any invader. This trait of this species is exploited by Japanese anglers to catch these fish and it works really well as these fish are caught easily. Tame cormorants are used in Japan to catch ayu fish. Other methods for capturing ayu fish are fly fishing, using a fish trap, and fishing with a decoy.

Ayu Fish Fun Facts

What do ayu fish look like?

This fish is quite small in size and ranges between 6–12 in (15.2-30.4 cm) in length. The unique ayu sweetfish is olive or light yellow in color and is distinguishable due to its sail-like dorsal fin, and ridged tongue. Its teeth are arranged at the side of the jaw on saw-edged plates.

The ayu fish is a small-sized creature that is of olive or yellow color!
*Please note that this image is of a delta smelt, a close relative of the ayu fish. If you have a picture of an ayu fish, please let us know at hello@kidadl.com

How cute are they?

These sweet-tasting fish that are very common in Japan are quite cute and attractive, especially when young. Their coloration is quite interesting as well.

How do they communicate?

Like their relatives, they communicate using motion, electrical pulses, bioluminescence, and chemicals.

How big is an ayu fish?

It is quite small in size and ranges between 6–12 in (15.2-30.4 cm) in length. It can grow up to the same length as the rockmover wrasse!

How fast can an ayu fish swim?

The speed of juveniles can range between 0.5-1 m/s (1.8-3.6 kph).

How much does an ayu fish weigh?

It ranges between 0.01-0.82 lb (4.5-371.9 g) in weight. The lower end of their weight range is the same as the weight of a female rainbow shiner.

What are their male and female names of the species?

Males and females of this species do not have specific names.

What would you call a baby ayu fish?

A young ayu sweetfish is called a fry!

What do they eat?

The ayu fish feeds upon water weeds, algae from rocks, crustaceans, sponges, worms, and aquatic insects found in rivers. The ayu fish itself is one of the most highly prized food fish. This food fish is consumed in the summer season.

Are they dangerous?

Yes, the ayu is very territorial about its feeding sites and will attack any creature who enters its territory in the river or sea. One sweetfish defends 107.6-215.3 ft2 (10-20 m2). Some anglers in Japan exploit this territorial trait. They introduce a live ayu on a hook into another ayu's territory, leading to the territorial ayu attacking the introduced ayu. These fish are largely harmless to people.

Would they make a good pet?

There are no known instances of the sweetfish being kept as a pet. However, given their territorial nature, an ayu should not be kept in a tank with any other fish.

Did you know...

Many people say that the ayu emanates a watermelon-like fragrance!

Is the ayu fish endemic?

The term 'endemic' is used to refer to a creature that is found in one specific area regularly. The ayu is endemic to East Asia.

Where can I find ayu fish?

The ayu, Plecoglossus altivelis, can be seen across the northwestern Pacific Ocean near the Hokkaido coast in Japan, southwards to China, the Korean Peninsula, Vietnam, and Hong Kong.

Here at Kidadl, we have carefully created lots of interesting family-friendly animal facts for everyone to discover! Learn more about some other fishes from our salmon interesting facts or rock hind facts for kids pages!

You can even occupy yourself at home by coloring in one of our free printable queen angelfish coloring pages!

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