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.
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'.