The first dorsal fin is black at the front.

第一个（刺背鳍是在前面的黑。

The shark's dorsal fin was cut off by the fisherman.

鲨鱼的背鳍被渔夫割了下来。

Its sail-like first dorsal fin provides stability while swimming.

帆状的第一背鳍在游动时提供了稳定性。

Its dorsal fin was in front of me. I was screaming for help.

它的背鳍就在我的前面，我尖声呼救。

His dorsal fin was down and his huge pectorals were spread wide.

它的脊鳍朝下耷拉着，巨大的胸鳍大张着。