[00:00.00]So we’ll continue today with the topic of fish movement and we'll focus on the role of fins. [00:11.51]You can think of things pretty much like the arms and legs of humans. It‘s what allows movement basically. [00:18.00]But as we will see they also do a lot more. [00:21.28]Before we go on with the function of specific fins, I just say a few general remarks. So you get an overall picture. [00:27.99]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. [00:39.22]That's right. Fish have to have a way to put on the brakes too.
[00:42.55]Now, some fish are so fast, they‘re not good at stopping even with their fins. Requiem sharks, for example. [00:50.91]You know, how sharks are built for speed. But these requiem sharks have difficulty stopping. [00:56.91]They're unable to brake themselves efficiently, so they must take sharp turns in order to slow down or stop. [01:04.40]Because of this, hmm, this brake problem. Requiem sharks avoid swimming into coral reefs. [01:11.81]Coral reefs are usually crowded, don't allow a lot of space for large fish to take sharp turns. [01:18.84]So these sharks roam around the outside of the coral reefs.
[01:23.01]Um, a fish lives in a 3 dimensional world, you know, with forces pushing and pulling it in all directions. [01:31.30]The forces I'm referring to are gravity, which pulls the fish downward. Buoyancy, which holds it up in the water, and something called drag.
[01:42.09]Now, drag means to slow down, to impede movement. [01:48.09]It's a term that applies to the effect of the force acting on any object moving through a fluid or through air. [01:55.66]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.
[02:04.39]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. [02:16.79]So, fins allow fish to keep from rolling or flipping over. They stabilize the fish's head.
[02:24.20]Fins are crucial for determining the speed at which fish travel, to change direction. [02:30.70]In a word, fins allow the fish to maneuver efficiently through the water. [02:35.60]Okay. Remember, most fish have two general types of fins.
[02:40.88]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. [02:52.69]The other type of fin is the paired fins at each side of the fish.
[02:57.38]For today, the caudal fin is the one will focus on. [03:01.06]The caudal fin, that is the tail fin. Is the main propulsive agent for most fish, it keeps them moving forward. [03:09.20]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.
[03:20.71]You'll find that fast, long distance swimmers have a very long and narrow caudal fin, which is very efficient. [03:28.18]Now, do all fish have caudal fins? No, not at all. [03:33.53]Some sea horses and eels get along without them just fine. [03:38.00]Well, a seahorse swims in an upright vertical position. It looks like its standing up, right. [03:44.19]So it uses a fin on its back, the dorsal fin, as if it were a caudal fin.
[03:49.23]And eels, well, don't really need to swim very rapidly. [03:54.09]And like I said, most are missing the caudal fin, but most fish do have caudal fins. [04:00.20]I give you two examples of caudal fins, and well see how they work. Okay? [04:04.56]Let's see. I focus on the tuna and the black fish. [04:09.59]The tuna's body is built for speed, but the caudal fin, the caudal fin is key here because its moon-shaped tail creates hardly any drag in the water. [04:21.05]And it can reach really high speeds of even 60 to 80 kilometers per hour and that's pretty amazing.
[04:27.50]Then there's the really interesting case of the blackfish, which has a rounded caudal fin. As you can see. [04:34.78]And in sudden bursts, it almost acts like a propeller on a plane that can even produce the sound that as an explosion. [04:42.27]I bet you never thought of fish fin could do that. [04:44.98]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.
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