Listen to a part of lecture in a marine biology class

请听一段海洋生物课堂讲座

So we’ll continue today with the topic of fish movement and we'll focus on the role of fins.

所以我们今天继续鱼类运动的话题我们将重点关注鱼鳍的作用。

You can think of things pretty much like the arms and legs of humans. It‘s what allows movement basically.

你可以想象一下,就像人类的胳膊和腿。它可以进行基本的运动。

But as we will see they also do a lot more.

但我们也会看到鱼鳍的能力不止如此。

Before we go on with the function of specific fins, I just say a few general remarks. So you get an overall picture.

在我们继续讨论特定鳍的功能之前，我先说一些关于鱼鳍的一般性评论，这样你就会有一个整体的感知。

Fins are mainly used for moving the fish forward for propulsion as it's called, but they’re also needed for stability, steering and braking.

鱼鳍主要用于推动鱼向前推进，但它们能用来保持稳定性，转变方向和停止运动。

That's right. Fish have to have a way to put on the brakes too.

没错，鱼有时也需要刹车，停止运动。

Now, some fish are so fast, they‘re not good at stopping even with their fins. Requiem sharks, for example.

有些鱼跑得很快，即使用鳍也不能停下来。比如安魂曲鲨鱼。

You know, how sharks are built for speed. But these requiem sharks have difficulty stopping.

你知道，鲨鱼天生就运动速度很快。但是这些安魂曲鲨鱼很难让自己停下来。

They're unable to brake themselves efficiently, so they must take sharp turns in order to slow down or stop.

他们无法有效地刹车，所以他们必须通过急转弯来减速或停止运动。

Because of this, hmm, this brake problem. Requiem sharks avoid swimming into coral reefs.

因为减速和停止的问题。安魂曲鲨鱼会避免自己游进珊瑚礁。

Coral reefs are usually crowded, don't allow a lot of space for large fish to take sharp turns.

因为珊瑚礁通常都很拥挤，没有空间留给大鱼来急转弯。

So these sharks roam around the outside of the coral reefs.

这些鲨鱼通常在珊瑚礁外面游荡。

Um, a fish lives in a 3 dimensional world, you know, with forces pushing and pulling it in all directions.

鱼生活在一个三维的世界里，你知道，在各个方向都有力在推它，拉它。

The forces in referring to are gravity, which pulls the fish downward. Buoyancy, which holds it up in the water, and something called drag.

那么这里所提到的力，主要指重力，把鱼往下拉的力；浮力，让鱼浮在水中的力以及阻力，把它往后拖的力。

Now, drag means to slow down, to impede movement.

拖的意思是减速，阻碍运动。

It's a term that applies to the effect of the force acting on any object moving through a fluid or through air.

这个术语适用于任何在流体或空气运动的物体所产生的力的效果。

So for instance, the force of air on an airplane, drag acts to pull the airplane in the opposite direction to the direction of motion.

例如，空气对飞机的作用力，空气产生的阻力正好和飞机的运动方向相反。

Well, all of these forces, gravity, buoyancy, and drag could be potentially dangerous for fish if they weren't for the fact that they have. Yep, you guessed it, fins.

所有这些力：重力、浮力和阻力，对鱼来说也会带来潜在的危险, 如果它们没有按照应有的功能来发挥。是的，你猜对了，是鳍。

So, fins allow fish to keep from rolling or flipping over. They stabilize the fish's head.

所以，鱼鳍可以防止鱼滚动或翻转。它们稳定鱼的头部。

Fins are crucial for determining the speed at which fish travel, to change direction.

鱼鳍是决定鱼前进速度和转变方向的关键。

In a word, fins allow the fish to maneuver efficiently through the water.

总之，鱼鳍能让鱼在水中高效地游动。

Okay. Remember, most fish have two general types of fins.

记住，大多数鱼有两种类型的鳍。

The first type is median fins. Median fins are located along the midline of the fish such as the dorsals on the back. And the caudal fins, the tail fin.

第一种类型是中间鳍，位于鱼的中线，比如背部的背鳍，和尾鳍。

The other type of fin is the paired fins at each side of the fish.

另一种类型的鳍是在鱼的两侧的一对鳍。

For today, the caudal fin is the one will focus on.

今天我们要关注的是尾鳍。

The caudal fin, that is the tail fin. Is the main propulsive agent for most fish, it keeps them moving forward.

尾鳍，也就是尾部，是大多数鱼类的主要推进部位，它使鱼不断前进。

Some fish have a broad tail that gives the fish a quick burst of speed from a standing position. And this is useful for going after a meal or swimming away from a predator.

有些鱼有宽宽的尾巴，这样使它们静止的时候就能快速地往前冲。这对于猎食或逃离捕食者是很有用的。

You'll find that fast, long distance swimmers have a very long and narrow caudal fin, which is very efficient.

你会发现，游得快、且长距离的鱼类都有一个又长又窄的尾鳍，这种尾鳍非常有效的。

Now, do all fish have caudal fins? No, not at all.

那么，所有的鱼都有尾鳍吗? 不，并不是所有的鱼。

Some sea horses and eels get along without them just fine.

有些海马和鳗鱼没有它们尾鳍，但也能自由游动。

Well, a seahorse swims in an upright vertical position. It looks like its standing upright.

海马是以垂直的姿势游动，看起来是直立的。

So it uses a fin on its back, the dorsal fin, as if it were a caudal fin.

所以它用背上的鳍，背鳍，就像用尾鳍一样。

And eels, well, don't really need to swim very rapidly.

鳗鱼，它并不需要游得很快。

And like l said, most are missing the caudal fin, but most fish do have caudal fins.

就像我说的，很多鱼都没有尾鳍，但大多数鱼都有尾鳍。

I give you two examples of caudal fins, and well see how they work. Okay?

我给你们两个尾鳍的例子，看看它们的作用，好吧?

Let's see. I focus on the tuna and the black fish.

让我们来看看。比如金枪鱼和黑鱼。

The tuna's body is built for speed, but the caudal in, the caudal fin is key here because its moon-shaped tail creates hardly any drag in the water.

金枪鱼的身体构造就会使得它游动速度很快，但尾鳍在这里是关键，因为它弯月形状的尾巴在水中几乎不产生任何阻力。

And it can reach really high speeds of even 60 to 80 kilometers per hour and that's pretty amazing.

金枪鱼的速度甚至可以达到每小时60到80公里，这是非常惊人的。

Then there's the really interesting case of the blackfish, which has a rounded caudal fin. As you can see.

还有一个非常有趣的例子是黑鱼，它有一个圆形的尾鳍，正如你们所看到的那样。

And in sudden bursts, it almost acts like a propeller on a plane that can even produce the sound that as an explosion.

在它突然起步时，它的尾鳍就像飞机上的螺旋桨，甚至可以产生爆发动力的声音。

I bet you never thought of fish fin could do that.

我敢打赌你从没想过鱼鳍能做到这一点。

And you can see how this is useful to a fish when it goes to catch something or tries to avoid a predator. It needs to accelerate in an instant.

你可以看到鱼鳍对一条鱼来说是多么的有用，当鱼去抓东西或者试图躲避捕食者的时候，或者在需要瞬间加速的时候。