Tail up-and-down or side-to-side?

April 27, 2012 9:21 AM

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 (9 answers total)

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

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

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