Are Sharks Fish?

(Last Updated On: November 8, 2022)

Everyone kind of has an idea of what a fish is–especially because they taste pretty good deep-fried. But when we think about sharks, we probably just think of them as this separate category of “shark” based on some arbitrary vibes we decided upon a long time ago and then never questioned. But have you ever stopped to think about it? Are sharks fish?

Well, they’re not mammals

We can just rule that out immediately, since they’re not warm blooded, nor do they produce milk. However, you could be forgiven for at least a little confusion since some sharks might appear to give birth to their pups live instead of laying eggs.

Turns out, this is only kind of the case. Once a pair of sharks mate, the female shark carries now-fertilized eggs for anywhere between five months and two years depending on the shark species. No really, dogfish shark gestate for between 22 and 24 months; the longest gestation period for any vertebrate. 

Baby sharks

Anyway there are three different ways baby sharks are born. Oviparity, viviparity, and ovoviviparity. 

Starting with oviparity, it’s the most simple. These sharks just straight up lay eggs. Pups eat their way out of their eggs and the parents remain pretty uninvolved once the eggs are laid. The extent of parental care is just finding a secluded place to deposit eggs. Horn sharks are kinda cool though, once laid the egg cases harden into a spiral-looking horn that protects them. 

Viviparous sharks give birth live, by just carrying the embryo through the entire gestation period and with a yolk sac placenta. Some sharks even make a kind of uterine milk. This is the closest you might get to a mammal, but sharks lack mammary glands. Viviparous reproduction is considered the most biologically complicated of the three, and is more common to larger shark species like the hammerhead as a result.  

Ovoviviparous sharks are maybe the most interesting. As the name might suggest, they combine both the previous reproductive methods. These sharks produce eggs–but they hatch inside the shark. The pup continues to develop for a while longer until they’re born. Sharks don’t just lay a single egg though, and multiple will hatch inside the mother shark during the gestation period. This is where baby sharks get a little metal. By metal, we mean cannibalistic–because the baby sharks will eat each other in the womb. 

Elasmobranch

The definition of a “fish” is actually absurdly diverse, which should give you an indicator of whether or not sharks are fish. Most broadly, a fish is any non-tetrapod (doesn’t have four limbs) craniate. Craniates are chordates (some kind of spinal cord) with a defined head and maybe a skull. Fish also have gills and fins. 

But fish aren’t like birds or mammals, they include a lot of different taxa (if you remember taxonomy from biology class). They include everything from lampreys to lungfish–and lungfish are actually closer relatives to tetrapods than they are other traditional fish. Which is… A direct contradiction to what we just laid out. This is why the use of the term “fish” to describe a biological group may be considered obsolete. 

More on fish being weird: Is Fish Meat? What Is Meat Anyway?

Anyway, long short, sharks are a type of fish. Specifically, they belong to the subclass elasmobranchii. This subclass includes rays and sawfish, and they are luckily more clearly defined than “fish.” 

The upper jaw isn’t fused to the skull and is articulated with the lower jaw. As you’d expect, they also have gills. Elasmobranchii also have rigid fins and the name is derived from Ancient Greek roughly meaning “plate gill,” which is in reference to the flattened gills you commonly see on sharks or rays. 


See if you know your sharks here.

About the Author:

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Kyler is a content writer at Sporcle living in Seattle, and is currently studying at the University of Washington School of Law. He's been writing for Sporcle since 2019; sometimes the blog is an excellent platform to answer random personal questions he has about the world. Most of his free time is spent drinking black coffee like water.

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