Fish poop: everything you ever wanted to know

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If you're a fish lover and think you know all there is to know about this adorable aquatic animal, here's the shocker: You probably don't. First, no one even knows how many different types of fish there are in the world. Currently, we know of over 33,000 species of fish; but scientists are constantly discovering more.

However, for ease of identification, fish are divided into three groups: jawless fishes (Agnatha), bony fishes (Osteichthyes) and cartilaginous fishes (Chondrichthyes). As the most diverse group of vertebrates in the world, fish may have distinctive features. However, they are all fish because they are cold-blooded, live in water, and have swim bladders, fins, and gills.

We know fish can swim and have specialized locomotor organs, but do they poop? What does their poop look like if you can? How often do they have bowel movements? We'll discuss these in more detail in this article.

Does fish poo and piss?

parrotfish poop
Fish have a cloaca (anus) that allows them to pass their waste.


Yes, fish can pass feces and urine , and you're about to learn how. First, like humans, fish have two kidneys (called the pronephros and mesonephros), which are primarily responsible for processing waste. However, they do not have bladders, and their urethras are much shorter than those of humans. So, in addition to filtering the blood, their kidneys also help remove waste products.

That is, fish have a cloaca (anus) that allows them to pass their waste. While some fish excrete urine and poo from the same place, other species may have different openings for defecation and urine. For example, the discus (symphysodon) defecates through the cloaca but urinates through the mouth, while the betta (Betta splendens) urinates through the anus.

In general, though, many saltwater fish urinate through their gills, while freshwater fish urinate through their pectoral pores after filtering through their kidneys. They urinate and exchange gas with their gills through osmosis.

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What does fish poop look like?

fish droppings
Healthy fish droppings are small and quickly dissolve in water.

©piya saisawatdikul/

Now that we've established that fish can poop, the next question is, "What does it look like?" Healthy fish poop is small and quickly dissolves in water. However, if the fish is constipated or has a parasitic infection, its droppings can become long and sticky. It's also important to note that fish poop does not stay one color, as its color depends on its diet.

For example, if a fish eats flakes, it will likely produce reddish poop because the flakes are full of bloodworms. Therefore, green fish poop indicates that they ate green foods such as peas. However, if the fish has not eaten for a while, its poop can take on a clear, whitish or brown appearance. Therefore, white poop may indicate malnutrition.

Another way to identify fish poop is by its texture and smell. Fish feces can smell, and aquarium owners may perceive an unpleasant odor emanating from the tank due to the buildup of excrement.

How often do fish poop and urinate?

If you're wondering how often a fish excretes feces and urine, the answer is "not often." Especially when one compares it to how often humans poop and pee. While humans can urinate and excrete feces multiple times a day, fish will typically urinate once a day and defecate a few days later if their kidneys are functioning optimally. That's because their meals take about a day to process and digest before being evicted. However, how often they eat can affect how often they have bowel movements — the more they eat, the more often they have bowel movements.

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For example, if a fish is constantly eating, it may need to poop every 2 days. However, if the fish eats less frequently, the defecation time will be much longer than 48 hours, and the intervals will be irregular. In fact, when a fish hasn't eaten for a long time, it can take up to four days for it to poop.

What do fish eat?

colorful fish
While some fish will target smaller organisms such as detritus and algae, other species will prey on meat in the form of birds.

© Henmi

Fish feed on a variety of food sources as they can be carnivorous, omnivorous or herbivorous. Their diet also depends on their environment, body size and biological makeup. So while some fish will target smaller organisms like detritus and algae, other species will prey on meat in the form of birds and small mammals. Examples of meals that make up a fish diet include other fish, small amphibians and reptiles, insects, worms, sponges, zooplankton, jellyfish, crustaceans, and molluscs.

Fish have keen senses, including sight, hearing and smell, that help them find food quickly. Knowing what various fish species eat is critical to feeding them properly and avoiding health challenges.

Why is fish poop important?

What is the use of fish poop? certainly. First, as with all other animals, fish droppings are a valid way to assess their health. Any deviation from normal discharge should be carefully investigated to ensure they are not ill.

Additionally, some aquatic plants rely on fish droppings for essential nutrients (especially phosphorus and nitrogen) that help them thrive. Fish poop provides food for bacteria and plays a vital role in the carbon cycle. In turn, bacteria help break down plants and animals.

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How to Remove Fish Poop from a Fish Tank

It is important to never allow fish poop to build up in the tank as it will mix with their food very quickly. When fish eat this contaminated food, they are likely to develop serious health and life-threatening problems.

The first step in removing fish droppings from a tank is to turn off all electrical appliances. Next, clean up the fish droppings, but always remember to remove the algae first. The next step is to remove about half of the water and clean the tank equipment and decorations. This step is important because fish can poop anywhere in the tank, and some droppings may end up in equipment and decorations.

Finally, fill the tank with treated displacement water and clean the outside of the tank.


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