pelvic fin

US /ˈpel.vɪk fɪn/
UK /ˈpel.vɪk fɪn/
"pelvic fin" picture
1.

腹鳍

either of a pair of fins on the underside of a fish's body, typically behind the pectoral fins, that help control direction and stability

:
The fish used its pelvic fins to maintain balance in the current.
这条鱼用它的腹鳍在水流中保持平衡。
Sharks have two pelvic fins located near their cloaca.
鲨鱼有两个位于泄殖腔附近的腹鳍