In fact, tunas must swim to breathe.
事实上，金枪鱼必须游泳才能呼吸。
Tunas, mackerels, and billfishes have even more sophisticated adaptations than these to improve their hydrodynamics.
金枪鱼、鲭鱼和长嘴鱼有比这些更复杂的适应性，以提高自己的流体动力学。
Because they are always swimming, tunas simply have to open their mouths, and water is forced in and over their gills.
因为它们总是在游泳，所以金枪鱼只需要张开嘴巴，水就会被强行灌进它们的鳃里。
Although most of their scales have been lost, tunas and mackerels retain a patch of coarse scales near the head called the corselet.
虽然它们的大部分鳞片已经消失，但金枪鱼和鲭鱼头部附近仍保留着一块粗糙的鳞片，称为胸甲。
Although most of their scales have been lost, tunas and mackerels retain a patch of coarse scales near the head called the corselet.
虽然它们的大部分鳞片已经消失，但金枪鱼和鲭鱼头部附近仍保留着一块粗糙的鳞片，称为胸甲。
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