If you are wondering do fish have kidneys you are not alone. This is one of the questions that get asked a lot by both fish keepers as well as anglers. Yes, all types of fish have kidneys. The shape and size of kidneys differ from one fish to another. The function also differs depending on whether we are talking about freshwater fish or saltwater fish.
Kidneys In Fish
The purpose of kidneys in all animals is osmoregulation. Kidneys in fish serve the same purpose. So, if someone has ever asked you do fish have kidneys? The answer is yes because fish also need osmoregulation.
The fish have a semipermeable skin which allows the movement of water and dissolved solutes to pass through.
Because the fish live in water, they need to regulate the movement of salts and water between their body and the surrounding water.
Kidneys serve the purpose of regulating water and salt and ensuring that the organisms have a balance between the two so that they can survive.
In fish, the kidneys help to regulate the interaction between internal body fluids and external water fluids. They are for the function of the kidneys in freshwater fish and saltwater fish differ slightly.
Fish Kidney Structure
Fish kidneys differ slightly from those found in mammals. Kidneys in fish are stretched, smaller and do not have a bean-shape like structure.
The kidney is also located towards the middle of the fish body. It is located almost halfway both lengthwise and height wise.
Kidneys in Freshwater Fish
In freshwater fish, the water is significantly dilute compared to the fluids inside the body of the fish. This type of fish needs kidneys to prevent excess loss of solutes.
There exists a significant concentration gradient between the water and the fish fluids. Naturally, the water would diffuse into the fish through osmosis and cause large amounts of water buildup.
The kidneys in freshwater fish help the fish get rid of excess water bypassing it out as urine. They also reabsorb useful salts that would be otherwise passed out in the urine.
This is the process that the fish used to maintain this critical balance. Freshwater fish produce and excrete large volumes of dilute urine that is mostly comprised of water.
Kidneys in Saltwater Fish
In saltwater fish, the kidneys function opposite of how they function in freshwater fish. In saltwater fish, the water around the fish is highly concentrated with salt and other solutes. The what the fluids inside the fish are dilute.
The concentration gradient between the two fluids means that the fish loses lose body fluid into the water through the process of osmosis.
If the process is to remain unregulated all the water from the body of the fish could be sucked out into the salty water that surrounds the fish. The fish counteracts this process by constantly taking in water to replace what it has lost.
However, constantly taking in water also means that the fish takes in large amounts of salts which can cause buildup in the body.
The kidneys are therefore useful for removing the excess salt and other harmful substances from within the fish.
The kidneys actively excrete salts while helping the fish retain water. In saltwater fish, the urine is highly concentrated.
Kidney Regeneration In Fish
Kidneys in fish have been shown to regenerate and restore full operation. In the majority of mammals, kidneys can repair themselves after an injury. However, in most of them, they don’t regain full operation.
Kidney regeneration in fish is an interesting concept that researchers hope to use in advancing medicine.
Other Internal Organs
The fish have other internal organs including the intestines, stomach, heart, spleen, and bladder. if you have ever gutted a fish you have definitely seen these organs.
In small fish, it is impossible to identify the different organs. However, in large fish, the organs are larger and an experienced person can identify them.
The elongated and narrow kidneys in fish play a significant role in keeping fish alive. The kidney works together with the other organs to ensure that critical processes in the fish happen as required.
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