How Fish Float

Fish are an exceedingly popular pet because they provide their owners with countless hours of relaxation by doing what they do best – swimming. Most people however are likely not to know the answer to an obvious question; how are fish actually able to swim? Unlike humans that tend to float in the water, fish swim at different levels because they have a swim bladder. We will discuss what the swim bladder is, what is does, and what happens to your fish when it does not work correctly.

What makes something float in water? The answer is air or anything lighter than water. A fish uses this knowledge by having an air filled space in its body that makes it lighter than water so it can float. A fish however does not always want to remain at the top of the water where it would be easy prey for wild animals or pet cats. Thus, fish need to be able to control the swim bladder to make changes in their swimming level. How do they do this? It is not a simple answer, as it varies between different types of fish.

There are many ways to categorize the swim bladders in fish. Firstly, there are certain types of fish that are able to swallow air to inflate their swim bladders. They do this through a connection or duct that runs from the esophagus to the swim bladder. The second type of fish is distinctly different from the first type in that they do not have a connection from the esophagus to the swim bladder. Instead, they have an extensive system of tiny blood vessels in the walls of the swim bladder that regulate the amount of gas within the swim bladder. Beyond this duct, another way to classify swim bladders is the number of chambers (sections). Additionally, some fish like the tuna do not even have a swim bladder. How do they stay afloat, you ask? They do not! These fish swim near the bottom. Therefore, the swim bladder has many variants but in the end they all serve the same basic function, to regulate the swimming level of the fish. If it wants to go deeper, it releases gas. If the fish wants to float higher it takes more gas into the swim bladder. This mechanism is very efficient, quite like the regulation device that scuba divers need to use to control their depth in the water.

Moving on, what do you think happens if fish are unable to control their depth in the water? The answer would be, they float! This is a very common problem in pet goldfish. The reason being, goldfish are the type of fish that have the connection from the swim bladder to the esophagus. However, they seem to have a predisposition towards food clogging in this connection. Why? It is believed that this may partly be because of the common spherical body shape in pet goldfish that ‘squishes’ the contents of the gut, making it easier for food to clog in the esophagus-swim bladder connection. Human feeding techniques also makes it easier for food to clog in the duct. We feed these fish dry foods that expand when they get wet, blocking the duct when swallowed by the fish. With a blocked duct, the swim bladder cannot deflate or inflate and the fish will be ‘suspended’ in place. They then find it very difficult to swim to the bottom (swim bladder problems can also make a fish sink and be unable to swim to the top). Even though this is the common reason fish float, there are countless other reasons such as viruses, bacteria, diet, and cancer, just to name a few. The variety of possible causes often makes it very difficult to cure a floating fish, so prevention is the key.

There are three key things you can try to do that will decrease your fish’s chances of having floating problems because it has a swim bladder problem:

  1. Have great water quality
  2. Pre-soak food
  3. Switch foods to gel-based foods

These tips for prevention will also help your fish to become healthier overall.

By Laura Platt- writer