noun
red carp; golden carp
Refers to an ornamental variety of common carp (Cyprinus carpio) with red or golden coloration, often kept in ponds.
庭の池に緋鯉が三匹泳いでいる。
Three red carp are swimming in the garden pond.
錦鯉 is a broader term for multicolored ornamental koi, while 緋鯉 specifically refers to red or golden varieties.
Compound of 緋 (hi, 'scarlet') and 鯉 (koi, 'carp'). The reading ひごい is a straightforward combination of the two characters' readings.