fin line

例句：

1. 1. The fish swims with its tail fins held up high.
   这条鱼用鳍高高地挥动着尾巴游动。
2. 2.The scientist used a microscope to observe the tiny fin lines on the fish's skin.
   科学家使用显微镜观察了鱼皮上的细小鳍线。
3. 3.The boat was propelled by the strong current, and the fin lines were visible in the water.
   船被强劲的水流推动，可以看到水中的鳍线。