pectoral fin

US /ˈpek.tər.əl fɪn/
UK /ˈpek.tər.əl fɪn/
"pectoral fin" picture
1.

either of a pair of fins situated on each side of a fish's body, typically just behind the gills, that correspond to the forelimbs of other vertebrates

:
The shark used its pectoral fins to steer through the water.
Fish use their pectoral fins for balance and braking.