Fish Pee Like Us to Regulate Their Bodily Fluids – They Also Poop and Fart

Key Takeaways on Fish Pee

• Fish pee just like humans do to excrete metabolic wastes. Some species produce a concentrated, somewhat yellow-hued urine that is quickly dispersed in their aquatic world.
• Besides water, fish pee is primarily made of nitrogen and urea, but the exact makeup differs among the 36,000 species of described fish, especially between saltwater and freshwater species.
• Most of the water, salt, and other chemical exchanges happen through the gills, with waste products being excreted through the cloaca and vent.

Like humans, fish pee to regulate their bodily fluids. Urination is a vital physiological process that helps humans to eliminate waste products and maintain fluid balance. Our kidneys filter water substances – urea, uric acid, creatine – from blood, which we then pee out.

Fish similarly excrete metabolic wastes, particularly excess water and ammonia, to osmoregulate, or balance their internal fluids with their external environment. How they do so depends on the type of water a fish is found in.

“Fish pee like you and me,” says Prosanta Chakrabarty, director of the Louisiana State University Museum of Natural Science.

Do Fish Pee?

An expert in ichthyology, the study of fish, Chakrabarty says that fish excrete ammonia, urea, and other components of pee from their kidneys and out of a cloaca or vent. Fish kidneys filter blood to produce urine, which is then excreted through this cloaca.

“Basically, it’s an all-purpose ‘pooper.’ And yes, they also poop and fart,” explains Chakrabarty. Gills, on the other hand, excrete a byproduct known as ammonia.

Besides water, fish urine is primarily made of nitrogen and urea, but the exact makeup differs among the 36,000 species of described fish, especially between saltwater and freshwater species.

Read More: Do Fish Feel Pain?

What Color Is Fish Pee?

While humans have a distinct pee color, fish pee is an excretion of waste, namely through their gills, rather than from a urinary bladder like humans.

Urea is a concentrated salt with nitrogen, a combination of carbon dioxide and ammonia. Sharks hold or excrete urea through the less concentrated urine, also to keep a better balance of salt in their blood. Some species produce a concentrated, somewhat yellow-hued urine that is quickly dispersed in their aquatic world.

How Fish Get Rid of Waste

Most of the water, salt, and other chemical exchanges happen through the gills, with waste products being excreted through the cloaca and vent. A cloaca is a primitive, single cavity at the end of both the urinary and digestive tracts found in animals like fish, birds, reptiles, and amphibians. Cloacas served as the root for the human evolutionary urinary system, says Chakrabarty.

“Except [fish] can do part or most of this job through a gas exchange in the gills. But they metabolize food and water and produce waste filtered through the blood, gills and kidneys that eventually come out of the vent or cloaca,” says Chakrabarty.

Because fish pee, that also means they drink the water in which they live. Unlike freshwater fish, those in the ocean extract salt from their surrounding seawater to osmoregulate or regulate their internal balance of water and solutes to maintain homeostasis.

“Fish drink so they can osmoregulate and balance salts in their body relative to the water they are swimming in. 'Drinking' is done more so in marine/saltwater species than those in freshwater, which can osmoregulate mostly through the gills and don't have to gulp water. They take in water through the mouth, and the exchange of gases happens mostly in the gills,” says Chakrabarty.

Understanding Fish and the Ocean

Understanding ichthylogy and marine science, including whether and how fish pee, is vital to our broader understanding of the ocean – and perhaps surprisingly, contributes to the chronology of human evolution.

“We evolved from fishes. We do what we do, including breathing through lungs, having nostrils that fill those lungs, having arms and legs, and big brains, all of which came from our aquatic ancestors. So did kidneys, lungs, and being able to pee!” says Chakrabarty.

In other words, ichthyology helps explain “how we got our funky anatomy as a fish out of water.”

Read More: Wild Fish Can Recognize Individual People, and Maybe Even Human Faces

Article Sources

Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:

• Science Direct. Osmoregulation
• Prosanta Chakrabarty. Director of the Louisiana State University Museum of Natural Science