Tail up-and-down or side-to-side?
April 27, 2012 9:21 AM   Subscribe

What advantages/disadvantages are there to swimming as fish do versus swimming as cetaceans do?

Fish propel themselves forward primarily with a side-to-side motion of their tails. Whales, dolphins, and porpoises, having evolved from land-dwelling mammals, have hips that are suited to up-and-down motion instead, and, thus, primarily propel themselves that way.

Are there any advantages/disadvantage of one way versus the other? (Bonus: are there any fish that swing their tail more like a cetacean?)
posted by glhaynes to Pets & Animals (11 answers total) 2 users marked this as a favorite
Can't answer the first, but for the bonus, does a flounder count?
posted by Grither at 9:23 AM on April 27, 2012

What comes to mind for me is that whales (I'm thinking humpbacks and sperm) need to come to the surface to breathe and then to dive deep, and the up and down motion would give them an assist on that. (I'm thinking of how I get to the bottom of a pool quickly from a standing position: I tend to give a good vertically-inclined kick as I descend.)

Fish (non-mammals) don't need to dive as far as I know, at least not the way whales do.
posted by Currer Belfry at 9:44 AM on April 27, 2012 [1 favorite]

Interesting question.

Yeah, I'm pretty sure that it has something to do with the fact that cetaceans have their breathing apparatus (the blow hole) on their back.

I would think that swishing back and forth would make this difficult to get a proper breath of fresh air. Fish don't really care about this because they use gills.

However, why fish don't use up and down motion to propel themselves through the water? I'm not sure if it's an advantage or not.
posted by WestChester22 at 9:59 AM on April 27, 2012

....I always thought that the reasons fish go side-to-side and mammals go up-and-down had more to do with the shape of the tail itself.
posted by EmpressCallipygos at 10:05 AM on April 27, 2012

Yeah from a hydrodynamic perspective the horizontal fin improves vertical mobility which is important for mammals which need to reach the surface to breathe. Side to Side fins are more suited however for maneuvering (or dodging predators) in the water.

This could also explain why cetaceans have generally evolved larger (Fewer potential predators).
posted by bitdamaged at 10:32 AM on April 27, 2012

I suspect advantages/disadvantages have less to to with the mechanics of up/down vs side-to-side than factors such as the presence or lack thereof of an swim bladder. Most rayed species of fish control their buoyancy (vertical movement) with an internal organ that can absorb/release gas from their bloodstream with very little cost in energy. The downside is most fish with swim bladders are limited to a relatively narrow range of depth because their swim bladders cannot cope with big quick changes, something that is rather dramatically and fatally illustrated when a deep-sea dwelling fish is brought to the surface and the pressure differential causes its swim bladder to expand so much that it and other internal organs are forced out of the fish's mouth. Being restricted to a specific band of depth narrows the opportunities for food sources, especially if the food moves out of depth or is otherwise depleted.

Cetaceans do not have this organ and are able to travel easily between the surface and the depths in pursuit of food, giving them command of many more regions and thus greater flexibility in food foraging. For some species of cetaceans, deep diving is an important feeding strategy.

Aquatic animals without lungs or swim bladders have to rely upon dynamic lift to change depth, hence the one of the reasons sharks have to swim or sink. It's also the reason why their pectoral fins are angled parallel to the ground like airplane wings.

Another factor is the presence or lack thereof of nerve endings on tails vs flukes and how that affects speed. Interesting article here.
posted by jamaro at 11:02 AM on April 27, 2012 [1 favorite]

Fish swimming is remarkably low-energy. The don't switch their tails to provide forward momentum so much as 'slalom' between vortices in the water, which enables them to hang almost effortlessly against currents, or swim against them. I'd guess cetacean swimming isn't quite as efficient as this due to blowhole issues and being warm-blooded, thus not having to be as economical with their energy.
posted by Kandarp Von Bontee at 11:03 AM on April 27, 2012

Yeah pretty much all swimming efficiency is related to creating and using vortices as described above. Offhand I'd say there is more variability amongst fish species than there is between fish and cetaceans. Think tuna vs puffer fish vs skate.

Also keep in mind cetaceans are warm blooded, so they are much faster swimmers than fish. Some fish, tuna, do warm their muscles to increase swimming speed. What's more efficient for a predator or open water species is totally different than a grazer or deep water dweller.
posted by fshgrl at 1:02 PM on April 27, 2012

The long-extinct marine reptiles Icthyosaurs had their tails like fish, side-to-side. And they needed to breathe just like cetaceans.
posted by ShooBoo at 1:27 PM on April 27, 2012

To add to ShooBoo's note about icthyosaurs, with the exception of turtles, modern aquatic and semi-aquatic reptiles (sea snakes, aligators, crocodiles, caimans, marine iguanas) swim by swinging their tails from side to side.

On a semi-related note: icthyosaurs were the first creature to give me some small sense of the scope of time passage from the Mid Triassic era to now. Think of: enough years had to elapse for a land-based reptile with four legs to return to the sea and evolve to an completely aquatic form with the same general form factor of a fish *and* then go extinct 30 million years ago. That's not even counting the time it took for the land-based ancestor to evolve from the muck in the first place. Mind. Blown.
posted by jamaro at 1:51 PM on April 27, 2012

All very interesting answers, thank you!
posted by glhaynes at 3:01 PM on May 1, 2012

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