Why do sharks have two penises?

By Patrick Cooney, Certified Fisheries Professional

The male shark circles, grabs onto the female’s pectoral fin with his mouth and bites down.  He keeps a tight grip with his sharp teeth while she remains motionless.  He slides in alongside her and curls his body in an arch.  The act is complete when he uses one of two claspers to copulate and impregnate the female.

Shark Mating2

Sharks mating.

What is a clasper?

Similar to a penis, claspers are an external appendage found on male sharks, skates, and rays that are designed to deliver sperm inside of a female.  However, they are dissimilar to a penis in that they are not an independent appendage, but rather a deeply grooved cartilaginous extension of the sharks pelvic fins.

Female shark and Male Shark with Claspers2

A male shark on the left (with claspers) and a female shark on the right.

Internal fertilization

Unlike a majority of fish that release eggs and sperm into the water for external fertilization, sharks fertilize their eggs internally.  A major disadvantage of internal fertilization is the limitation on the number of young one can have at one time because growing young internally takes up space.  Conversely, a major advantage of internal fertilization is the extended period of parental care that increases long term survival.

Shark Birth and Egg

Sharks give birth to live young or fertilized eggs.

Sperm delivery

In order for female sharks to give birth to live young or fertilized eggs, males must be able to deliver sperm internally to the female.  The clasper, just like the penis, is another of evolution’s unique methods for this delivery.

Shark Clasper

Shark claspers and pelvic fins.

But why are there two claspers?

Male sharks have two claspers because sharks have two pelvic fins.  The claspers are simply a modified portion of the pelvic fin, and since there are two pelvic fins, there are two claspers.

Do they use both at the same time?

Interestingly, research suggests that sharks only use one clasper at a time.  Shark mating has rarely been observed, but when observed, often involves the clasper on the opposite side of the body from where it has sidled up to the female.  Perhaps this allows a better range of motion.

Are there other fish with penis-like appendages?

Another group of fish that are not closely related to sharks have also developed a penis like appendage strictly for the purpose of sperm delivery.  Subsequently, the females in this group also give birth to live young.  The group (Poeciliidae) as a whole are called live-bearers because of this distinguishing trait.  Unlike sharks, the penis-like appendage on these fish is not a part of the pelvic fins.  Rather, this appendage, called a gonopodium, is part of the anal fin.  Since these fish only have one anal fin, male live-bearers only have one gonopodium instead of two claspers like sharks.

Gonopodium

Male Poeciliidae fish have a single gonopodium on their anal fin.

Please follow The Fisheries Blog on Facebook and on Twitter (@FisheriesBlog).  Also, enter your email on the top left section of this page to receive an email of our weekly article on Monday mornings.

11 responses to “Why do sharks have two penises?

  1. Yes muhammad, fish do have different organs that produce the same chemicals that we use. However, they use them in seemingly different ways. Great question, glad to help.

    • dear kyle, please tell me the name of fish which we can easily eat and has got less mercury in it thanks in advance

      • Sorry, rejorden. Was in Melbourne Australia studying the blue ringed octopus. Thanks for the question but honestly the amount of mercury in a single male shark would be about the same as in a light bulb. However, distributed throughout without mixed with iron and other chemicals related to blood that lower and raise depending on level of salt and the level of nutrition the shark gets.

  2. Thanks for these valuable informations.One doubt I wish to ask..
    Are the claspers connected to the testes and the sperms deposited through claspers..?

  3. Are there photos or videos of great whites mating? Is there some sort of truth about Orcas turning a great white on its back to kill them?

    • I’m sure there is. If you can’t find them I can assure to you that I will point point you in the right direction

  4. ~~ I would be orgasmic to hear your explanation on how these things “evolved” over millions of years, while sharks were unable to reproduce, and if your answer involves some prior form of copulation, why did they “evolve” to this unlikely way of doing things.
    We humans have a difficult method, but I dont see us “evolving’ to another way, altho we seem to be making an attempt, every time we have at it.
    You folks’ attempts to seriously present a case for evoo are hilariously rediculous….
    kenn

Please leave a thought provoking reply. We reserve the right to remove comments deemed inappropriate.

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s