Table of Contents
Do Fish Pee?
Like most living vertebrates, fishes do in fact pee. Fishes have two kidneys located above their swim bladder that filter waste from their blood. This waste is then discarded as pee into the surrounding water.
Fish kidneys filter wastes in their blood quite slowly. This is because their kidneys have a lot of additional responsibilities
Apart from filtering and processing wastes from the blood into pee, fish kidneys are also tasked with manufacturing blood cells. This is because, unlike humans, fishes don’t have bone marrow. So, half of a fish’s kidney filters blood wastes and the other half of the fish’s kidney makes blood cells.
How Do Fish Pee?
Fish actually can pee in many ways!
They can get rid of their pee either through their gills or through a urinary pore on the back end of their body (near the tail). Fish pee is also pretty toxic. This is because most fish are ammoniotelic. This means that when certain fish pee, they release nitrogenous waste in the form of ammonia a highly toxic chemical.
However, there are a few fish that do not release ammonia when they pee. These fish, including sharks and rays, are cartilaginous fish, and their skeletons are made from cartilage . Rather, their pee contains urea – another type of nitrogenous waste.
When Do Fish Pee?
As animals that live underwater, fishes pee a little bit almost all the time. They can do this as they do not have urinary bladders that can store urine, so they release a little bit of pee whenever they want (and wherever they want!)
There are three types of fish in the world: freshwater, saltwater, and brackish fish. Depending on the type of fish, the amount of pee released differs.
For example, freshwater fish, like koi, pee a lot more than saltwater fish, like salmon. This is because freshwater fish are a lot denser than the water that surrounds them and hence the surrounding water constantly moves into their bodies via passive diffusion . So, in freshwater fish, their kidneys work overtime to remove all the extra water that they filter through.
In contrast, saltwater fish pee a lot less, as they live in water that is denser than their bodies. They have the opposite problem of trying to retain more water in their body. So, in turn, they pee rarely as compared to their freshwater cousins.
Finally, brackish fish that live in waters with little or low salinity , like catfish or tarpon, pee more than saltwater fish but less than freshwater fish do. This is because they’re highly adaptable and can keep adjusting to varying levels of external water salinity.
Why is fish pee important?
Although fish pee is toxic, it is still quite useful to the ecosystems that the fish live in. This is because fish pee is important to water-based ecosystems. For example, fish pee has an especially positive impact on coral reefs. A recent study concluded that if fish pee levels drop in a certain location (due to overfishing, maybe) that region also ends up suffering from a loss of coral reef biodiversity.
This is because coral reefs get essential nutrients from fish pee, like phosphorus and nitrogen. This process is known as nutrient recycling. Fish pee is literally recycled into essential nutrients that boost coral reef growth and health.
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Flesch Kincaid Grade Level: 7.7
Glossary
Vertebrates: A group of animals that have a backbone, either made of cartilage or bone
Swim Bladder: An organ in fish that helps them stay afloat.
Gills: A organ present on either side of a fish’s face that helps them breathe.
Urinary Pore: A hole present on the rear end of a fish’s body through which they pee.
Nitrogenous Waste: Waste products that are generated after blood is filtered by the kidneys.
Cartilage: A type of strong and flexible tissue that makes up the skeleton of animals like sharks and rays.
Urea: A type of chemical found in nitrogenous waste.
Ammonia: A type of chemical found in nitrogenous waste.
Salinity: The density of salt that is present in a water body.
Ecosystem: The sum total of all the living and non-living parts of a particular area
Passive diffusion: When water moves from a place with lower salt concentration to a place with higher salt concentration
References
Lund, Arendse I. Question of the Week: Do Fish Pee? October 2, 2018. https://blogs.ucl.ac.uk/researchers-in-museums/2018/10/02/question-of-the-week-do-fish-pee/#:~:text=Fish%20have%20kidneys%20which%20produce,provides%20food%20for%20the%20fish.
Dr. Sanders, Jessie. Do Fish Pee? December 7, 2021.
https://cafishvet.com/fish-health-disease/do-fish-pee/
Ma, Michelle. Big fish — and their pee — are key parts of coral reef ecosystems. August 16, 2016.
https://www.washington.edu/news/2016/08/16/big-fish-and-their-pee-are-key-parts-of-coral-reef-ecosystems/#:~:text=When%20fish%20urinate%2C%20they%20release,and%20growth%20of%20coral%20reefs.
Stemco. How do other animals pee? August 2, 2021.
https://stemco.org/how-do-other-animals-pee/
Fish that eat algae
https://www.smorescience.com/fish-that-eat-algae/
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