10 Bizarre Facts About Fish Genitalia And Their Reproductive Rituals

How do fish reproduce, and where do fish babies come from? Unsurprisingly, fish aren't the only creatures with unusual mating rituals and genitalia. But how different are fish from humans, and how exactly do they populate the ocean full of so many colorful and diverse types of fish? Believe it or not, some fish penises are sort of like those of humans - they're long appendages that stick out from their lower torso. Others have internal organs that serve as penises but don't resemble those of other animals at all. Each species of fish has a unique set of genitals - including one that has a penis-like organ on its head. 

So, if you're interested in learning about how fish procreate, keep reading.


  • Some Fish Have Male and Female Sex Organs And Can Change Genders

    Although all clownfish are born male, when the alpha-female of a school of clownfish passes, a male will need to take her place. All clownfish are born as sequential hermaphrodites, meaning they possess both sets of sex organs but only display one gender at a time. Meaning, fish are born male but can later switch to female.

    This is usually done by the dominant male, who then switches his role from main male breeder to main female breeder. However, clownfish aren't the only aquatic-dwellers that switch up their sex organs. The Indo-Pacific cleaner wrasse is known to make the switch from female to male if the alpha male is removed from their mating harem. 

  • Larger Gonopodium, Larger Brain

    Larger Gonopodium, Larger Brain
    Photo: Toniher / Wikimedia Commons / Public Domain

    Scientists have discovered fish with bigger penises breed fish with bigger brains. Male mosquitofish with larger "gonopodiums" (a fin that is modified to be the equivalent of a fish penis) are better at coercing females to mate with them as opposed to male fish that are less endowed.

    Scientists' studies indicate that penis length might factor into this and their research also revealed that female offspring of the large-penis fish had brain sizes that were an average of 4.6 percent to 6.5 percent larger than the offspring of male fish with smaller penises. Although the difference was significantly larger for the female offspring, there was no change in brain size for the male offspring.

  • Some Fish Mate Through External Fertilization

    Many fish reproduce simply by excreting their reproductive materials - sperm and eggs - into the water so that they will unite, be fertilized, and turn into offspring. It's called broadcast spawning, or external fertilization, and by doing this, they're "broadcasting" their genetic code into the water.

    Female and male fish release their eggs and sperm into the same area of water at the same time, and let nature take care of the rest. However, the eggs need to be continuously suspended in the water by a current. If a current isn't present during fertilization, the eggs will sink to the bottom and die.

  • There's A Fish With Genitals On Its Head

    There's A Fish With Genitals On Its Head
    Video: YouTube

    Discovered in the waters of Vietnam's Mekong Delta, the phallostethus cuulong is a fish with a priapium, or fish version of a penis, located on its chin.

    The priapium features a sawlike hook used to attach to the female during mating. The genital opening of females is also located in the throat.