also: ひお
noun
whitebait; immature sweetfish
Refers specifically to young sweetfish (ayu) when they are small and translucent, often caught in spring. The term can also be used more broadly for similar small fish used as whitebait.
春になると、川で氷魚がとれる。
In spring, whitebait can be caught in the river.
氷魚の天ぷらは季節の味だ。
Tempura of immature sweetfish is a seasonal delicacy.
The kanji 氷 (ice) and 魚 (fish) likely refer to the translucent, ice-like appearance of the young fish. The reading ひうお is a kun'yomi compound, with ひお as a contracted form.