noun
pelvic fin; ventral fin
The pair of fins located on the underside of a fish, corresponding to the hindlimbs of land vertebrates.
魚の腹鰭は、体のバランスを保つのに役立つ。
The pelvic fins of a fish help maintain its balance.
この図鑑では、腹びれの位置で種類を見分ける。
In this field guide, species are identified by the position of the ventral fins.
Compound of 腹 (はら, belly) and 鰭 (ひれ, fin). The reading はらびれ is a straightforward combination.