pectoral fin
US /ˈpek.tər.əl fɪn/
UK /ˈpek.tər.əl fɪn/
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
:
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The shark used its pectoral fins to steer through the water.
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Fish use their pectoral fins for balance and braking.