Fauna
Fish

Ayu

Plecoglossus altivelis

Also known as Ayu Sweetfish, Sweetfish

Ayu are amphidromous fish native to East Asia, spending winter in coastal marine waters before migrating up clear rivers in spring. Adults establish distinct territories on sunlit riverbed stones, using comb-like teeth to scrape off algae and diatoms. Famous for producing a natural fragrance reminiscent of sweet watermelon or cucumber, they hold a prominent place in regional river ecology and culture.

AmphidromousMigratoryFreshwater
Ayu reference1 / 5
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Data DeficientConservation statusIUCN Red List categoriesLCNTVUENCREWEXData Deficient — not placed on the risk ladderRed List categories, explained →
Key facts
Diet & preyBenthic Algae, Diatoms, Mayfly Larvae
Predators
  • Grey Heron
  • Crested Kingfisher
  • Largemouth Bass
ThreatsDam construction, water pollution, and habitat degradation
HabitatsClear coastal streams, rivers, and estuaries
Life span1–3 years
Classification
  1. FamilyPlecoglossidae
  2. SpeciesPlecoglossus altivelis
Range & activity
Range data is not available yet.
Safe observation
Interaction riskLow
  1. Low
  2. Moderate
  3. High
  4. Very high
Why interaction risk is low
Safe to observe at a normal distance.
What to notice
Recognizable by an olive-green back, golden patch behind the gill cover, and bright yellow fins.
Support conservation
Observe quietly from riverbanks or bridges without wading through gravel spawning beds.
Responsible observation
  • Observation: Look for territorial grazing tracks on algae-covered river stones.
  • Seasonal Timing: Watch for migrating juveniles in lower river reaches during spring.
Related species
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