If mermaids are half human and half fish, how do they use the bathroom? Would they pee through their skin and gills as some fish do? It’s actually not as easy to answer as one might think.
Mermaids would most likely relieve themselves in the ocean just like all other sea animals. They might poop through their anus or a hole in their tail called a cloaca. Peeing would likely happen through a urinary tract as in dolphins, not by peeing through gills.
Let’s have a closer look at how this could work for these mythical creatures.
How do mermaids go to the bathroom?
When mermaids need to go to the loo, where do they go? To a private place like we do or do they just use the ocean as their toilets like fish and other marine life do.
Well, even though mermaids are half-human, it seems unlikely that they build toilets and sewage systems underwater. They actually don’t need to because the ocean perfectly cleans itself!
When an animal defecates in the ocean, thousands of small microorganisms eat it up within a short amount of time.
That means mermaids would most likely just poop and pee into the ocean whenever they need to. Just like all the other sea animals.
How do mermaids poop?
Mermaid defecation is a rather complicated matter because mermaids are both human and fish. The fact that the lower half of a mermaid is the fish part could give us some hints about how they might poop though: like other fish.
Most fish poop through an anus. It is an opening that that is exclusively for excrements. We humans have an anus as well, just like many animals.
Others use a so-called cloaca, which is a hole on the bottom side of their tails that is used for defecation, urination and reproduction. So cloacas are used for several differnent purposes. They are common in birds and some fishes like sharks.
For example, in sharks the cloaca is located just below the pelvic fins at the bottom side of their tail.
In this picture you can see where the anus and cloaca is located on fish and where it would be on a mermaid:
In this video you can see a shark pooping through its cloaca:
There is however one problem: As I wrote in my post about whether mermaids could exist, it is biologically not possible, that a creature has both mammal and fish body parts.
In my post about how mermaids reproduce I argued that biologically speaking it would make more sense if mermaids would be full mammals.
If we assume this, then they would also defecate like dolphins and other marine mammals. Dolphins in fact, also poop through an anus on the bottom side of their tailes.
How do mermaids pee?
Just like with the other excretions, mermaids would also more likely pee like fish because their lower body is a fish-tail. Or alternatively like a sea mammal like dolphins.
Fish actually urinate in a few different ways. Most fish pee either through a so-called pore at the bottom side of their tails and some even get rid of the waste through their skin or gills, meaning they basically pee through their skin and or gills.
An example of fish that urinate through their skin are sharks. They actually use a special type of this way of urination. Their urine gets absorbed in their flesh and then leaves the body through the shark’s skin.
Generally speaking, fish that live in the ocean do not pee much at all. They only do it once a day or every two days.
That’s because fish in the ocean constantly loose water via osmosis because of the high amount of salt in the water (higher than in their body). So they need to drink a lot of water all day long and filter out the salt and waste (pee) through their gills.
For marine mammals this does however not apply.
Do mermaids have periods?
Human women have periods as we all know. But what about mermaids?
It is unlikely that mermaids would have periods because in the ocean the blood would attract predators like sharks and get the mermaids into dangerous situations. Since mermaids are half fish from their waist down and fish do not menstruate at all, mermaids would likely not menstruate either.
In fact, only very few species of mammals menstruate at all: Besides humans, it is mostly apes and monkeys, but also some species of bats and the small elephant shrew (a mouse).
Other marine mammals like dolphins for example reabsorb their uterine lining and do not loose any blood during during their reproductive cycles. So, it could be similar for mermaids.