anal fin
The fin on the underside of a fish near the tail.
The anal fin of this fish is elongated.
図鑑で尻鰭の形を確認する。
Check the shape of the anal fin in the illustrated guide.
Tail fin or caudal fin.
Pectoral fin, on the side of a fish.
Standard kanji spelling for 'anal fin'.
Alternate kanji spelling using 臀 (buttocks).
Compound of 尻 (shiri, 'buttocks, rear') + 鰭 (hire, 'fin'). The kanji 臀 is a less common variant for 'buttocks'.