How do fish float?

Fish can provide countless hours of entertainment and relaxation for their owners just by doing something that comes very naturally to them: swimming.

They live in a three-dimensional environment that requires them to move not just forward, backward and side to side, but up and down as well. But how are they actually able to do this?

For an object to float in water, it requires air or anything lighter than water. Fish are able to float because they have an air-filled space in their body-called a swim bladder-that makes them lighter than water. However, a fish doesn’t always want to be at the top of the water, so for this reason, fish need to be able to control their swim bladder. If the fish wants to go deeper, it releases gas. If it wants to float higher, it takes more gas into the swim bladder.

There are two main types of swim bladders, while some fish, like tuna, have no swim bladder at all. That means these fish can’t float; they always swim near the bottom. The two main types are:

  • Fish that have a connection from their esophagus to the swim bladder-they swallow air to inflate their swim bladders
  • Fish with an extensive system of tiny blood vessels in the walls of the swim bladder-the vessels regulate the amount of gas within the swim bladder

Some fish, like pet goldfish, may have trouble regulating their swim bladders. They are part of the first type, whose esophagus is connected to their swim bladder. Due to human feeding techniques, it is common for their esophagus to become clogged. We feed them dry foods that expand as they get wet, which can block the duct when swallowed by the fish. When they can’t inflate or deflate their swim bladder, it will cause them to become stuck and unable to swim to the top or bottom. While there are other reasons that a fish might float, like viruses, bacteria or diet, a clogged esophagus is the most common and is easily preventable.

There are three key things you do that will help prevent your fish from having trouble floating due to a swim bladder problem:

  • Keep the tank’s water at a high quality
  • Pre-soak food
  • Change to a gel-based food

These tips will also help your fish stay healthier overall.

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