Salt water fish are used to living in salt water environments, so when they are placed into an aquarium of fresh water they can become stressed out. In this article, we will explore how a salt water fish would respond if it is put into an aquarium of fresh water and the effects it would have on its health.

What is Saltwater Fish?

A saltwater fish is a type of fish that lives in salt water. They are different from freshwater fish because they have special salt glands that allow them to live in seawater. Freshwater fish do not have these glands and must live in fresh water. Saltwater fish can be found in oceans, seas, and lakes.
Most saltwater fish are caught in the wild, but some are raised in captivity. Saltwater fish can be used for food, fertilizer, or oil.

What Effect Does Fresh Water Have on Saltwater Fish?

A saltwater fish should be adjusted to the new water if it is being moved. Most fish will do well with a few changes, like more frequent swims and an increase in food. Some fish, such as cichlids, may need to be put into a separate tank or aquarium if they are only going to live in fresh water.

What to Do If You Find a Saltwater Fish in Your Aquarium?

If you have a saltwater fish in your freshwater aquarium, it is important to make a plan to move it. Saltwater fish cannot tolerate the high levels of water saltiness found in freshwater aquaria, and can quickly become sick or die. There are a few options for moving a saltwater fish into fresh water:

  1. Transition the fish slowly over a period of several days by gradually lowering the salt level in the aquarium while keeping the temperature stable. This can be done by adding water from a freshwater source, boiling it, or using a desalination unit. Be sure to test the water first to make sure it is suitable for swimming.
  2. If you cannot transition the fish gradually, try transferring it all at once by using ice or cold water to shock the fish and make it swim away from the aquarium. Make sure to use cold water only – extreme cold will kill the fish.
  3. If you cannot transfer the fish or if it is too dangerous, you can euthanize it and replace it with a new saltwater fish.

The Experiment

If you put a saltwater fish in an aquarium of fresh water, it will most likely die. Aquariums are designed to accommodate different types of water and living creatures, but mixing the two can be harmful to both. Saltwater fish are used to a salty environment where they can swim freely and find food. In a freshwater aquarium, their food options are limited and they may not be able to find enough oxygen to survive.


Saltwater fish are used to living in saltwater and respond differently if put in an aquarium of fresh water. For instance, a common saltwater fish, a guppy, would be unable to survive in freshwater and would likely die. Other fish, such as goldfish, may take some time to get used to the new environment and may need to be kept in smaller tanks until they are comfortable.


The saltwater fish would likely be stressed by the sudden change in environment, and would likely require time to adjust. If kept in an aquarium with fresh water, the fish would likely get sick from the change in water quality.


If you were to put a saltwater fish in an aquarium of fresh water, how would it respond? If the fish is adapted to living in salty water, it would likely become sick and die. Aquarists often keep saltwater fish in tanks of fresh water so that they can see how the fish react when transferred from one type of water to another.