๐Ÿณ Do Fish Pee?

Yes, fish do pee. Urination in fish helps to remove the undesired soluble substances and excess water from the body. It not only helps them to regulate their internal environment (homeostasis) but it also provides nutrients to corals and other aquatic animals.

Image credit: C Watts

Can fish pee?

Have you ever wondered can fish urinate as human do?

Yes, fish can pee as well as poop. Similar to humans, fish too have kidneys that produce urine. You will be surprised to know that the pee (urine) of fish is very important for other aquatic living such as corals. The frequency of peeing in fish depends on the tonicity of the surrounding water. Fish living in oceans and brackish water pee less as compared to fish living in rivers and lakes.

Before we understand how the excretory system works in fish, letโ€™s try to know why fish urinate.

Do You Know?

An 85 meter long fin whale weighing up to 160,000 lbs can produce about 257 gallons of urine in a day.

Read: ๐ŸŸ Can Fish See In The Dark?

Why do fish pee?

The obvious reason for the fish body to produce pee is to remove unnecessary and undesired waste. However, in the case of freshwater fish, the primary reason for urinating to keep a balance of fishโ€™s internal environment (homeostasis) with the surrounding environment. Fish living in the freshwater and the saltwater face issue to maintain a constant concentration of water and solute such as salts. Urination helps fish to remove unnecessary substances such as waste products and excess water from the body. The kidney plays important role in maintaining proper balance and a relatively stable internal state despite changes in the external surrounding. Some fish such as salmon who frequently travel from freshwater to saltwater and vice versa, have evolved such that they can adjust their physiological process according to the external environment.

Fish anatomy, Image credit: Sharon High School

Read More: ๐ŸŸ Can a fish survive in milk?

How do fish pee?

Fish removes waste from their body through gills, skin, and urinary pores. The excretory system of the fish is responsible for the production of pee (urine) which contains excess water and undesired soluble substances. The excretory organ of the fish is consists of kidneys, ureters, and urinary bladder.

Kidneys: The kidney is the most important part of the excretory system which helps to maintain the proper concentration of salt and water in the fish body. The shape of the kidney varies with different species of fish. There are two kidneys in fish: the head kidney, and trunk kidney.

Head kidney is non-excretory organ consist of steroidogenic interrenal cells, chromaffin cells, and hematopoietic tissue. It plays important role in the initiation of the immune system in teleost fish. The gills of these teleost fish helps to get rid of ammonia.

Trunk kidney is also known as the posterior kidney. It contains filtering nephrons along with hematopoietic cells. The nephrons are the functional unit of the kidney which regulates water and soluble substances in the blood. It filters blood by reabsorbing the necessary substances and removing the waste in the form of urine.

The waste from the head kidney exit through gills while the trunk kidney waste exits through urinary pores.

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Urinary Bladder: Teleost fish have a bladder to store waste fluid from the kidney. It is important to note that a few fish lack urinary bladder.

Ureters: The trunk kidney is connected to the urinary bladder through tubes called ureters. The waste substances and excess water from the kidney get transported through the ureters to the urinary bladder.

The waste stored in the urinary bladder exits the body through urinary pores in the form of urine.

Read: Do Fish Have Tongues?

Why freshwater fish urinate more than the saltwater fish?

The freshwater fish pee or urinate more than the saltwater fish because of the salinity of their surrounding environment.

In freshwater, the concentration of salt in the surrounding water is less than the concentration of salt in the fish body. Due to this gradient in salt concentration, the surrounding water enters into the body of fish through osmosis. To avoid swelling of the body due to water, freshwater fish urinate frequently to remove excess water.

The surrounding condition of the saltwater fish is opposite to that of freshwater fish. The salt concentration of the surrounding water is more than the concentration inside the fish body. This difference in salt concentration causes fish to lose water to its surrounding water. Therefore, to prevent dehydration, saltwater fish drinks more water and urinate less.

Due to this difference in the environment, freshwater fish cannot survive in salt water and vice versa. However, note that few fish such as salmon can survive in both freshwater and saltwater. They have the ability to alter their internal physiological processes according to their surrounding conditions.

Read: ๐Ÿ  Can Fish Drown?

How frequently fish pee?

The frequency of the urination in fish varies with different fish depending on their surroundings. Fish found in lakes and river pee more often than the fish living in the sea and ocean to avoid swelling by osmosis. While the fish living in saltwater and brackish water urinate less to prevent dehydration.

In saltwater fish, 90% of the nitrogenous waste gets removed through their gills while the brackish water fish have less ability to remove the nitrogenous waste through their gills. Therefore, they depend more on their trunk kidney to remove waste. The bladder in freshwater fish doesnโ€™t act as a storage organ. Freshwater fish such as rainbow trout use their bladder to reabsorb sodium and water.

Read: How Do Fish Taste?

Is fish pee good for corals?

Yes, fish pee plays important role in the growth of the corals. The fish urine contains phosphorus and ammonium which essential nutrients for the survival of the corals. Species like sea anemones and algae also depend on the fish urine for nutrient supply. Therefore, biodiversity living in the oceans heavily relies on fish urine.  

According to a study, corals are so desperate for fish pee that the nutrient capacity is reduced by 50% due to overfishing and lack of protection. It may take 35-60 years for reef fish biomass to recover from the depleted levels.

Corals, Image credit: pickpik

Do goldfish pee?

Yes, goldfish do pee and poop. The urine exists through the urinary pore (external opening) present on the body.

Read: โญ How Do Starfish Eat?

Do betta fish pee?

Yes, betta fish pee similar to other fish. They also remove waste substances such as ammonia from their gills and excess water and soluble substances from the vent.

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Professor Atom

View posts by Professor Atom
Professor Atom is a science enthusiast and alumni of IIT Bombay. According to him, every question can be solved with curiosity and mind mapping. ( Curiosity = Asking Questions = Learning )

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