noun
razorfish; Aeoliscus strigatus
A small, elongated marine fish with a sharp-edged body, found in tropical waters. The Japanese name literally means 'heko sweetfish', but it is not related to ayu.
水族館でヘコアユが逆立ちして泳いでいた。
At the aquarium, the razorfish were swimming upside down.
The name ヘコアユ is a compound of 兵児 (heko, a type of traditional sash) and 鮎 (ayu, sweetfish), but the exact reason for the name is uncertain. The fish is not related to ayu.