Keeping fish healthy and happy is a skill that can be easily learned. One major component of fish health is facilitating their osmoregulation system. This system is quite significant for fish to stay alive as it determines the balance of both fluid and salt inside the fish itself. The more salty the tank water, the harder the fish’s system must work to maintain proper balance. Make sure to note the salt levels in a fish’s normal environment before purchasing and adding to your aquarium. The osmotic pressure (salt level) a fish can take depends upon their evolutionary status and natural habitat. For instance, a freshwater fish’s tolerance for salt is very low. Thus the osmotic pressure for a tank to include a fresh water fish must be maintained to a similar level as that of their natural habitat. This same rule of thumb is to be used for marine life as well.

There are fish that live in brackish water (a combination of fresh and salt water) and fish who travel between salt and fresh water. These types of fish have a high tolerance for changes in osmotic pressure. Salmon are an example of this type of fish.

The osmoregulation system of fresh water fish balances their bodies to maintain a slightly higher level of salt in the body in comparison to the surrounding water. The fish’s gills take in the water, removing the oxygen and then flushing the rest out as urine. Their bodies are always regulating water versus salt. Taking marine life into account, their bodies maintain a lower level of salt than that of their environment. Their osmoregulation system is consistently adding water to their bodies because the osmotic pressure is always pushing salt in.

These are important facts, because they can help in the event of having a sick fish. If a fish is ill, lowering the salt level of the aquarium will help the fish reduce the energy used for its osmoregulation system. If the energy for this system is reduced, it can then divert more energy to its immune system so that it can heal.

When creating an aquarium think of the best aquatic ecosystem, the ocean. It is 77% of the world’s surface, but more importantly has little variation in salt levels, even during season changes. The osmotic pressure changes more significantly in lakes and rivers. Most sea life is only equipped to handle up to a 2% change in salt level per day. Keeping this in mind when adding new fish to your tank, make sure to maintain a lower level of salt in the water will help the fish adjust to its new environment. It may take up to three weeks for full adjustment to take place. Once the fish is healthy and ready to withstand a more natural habitat, start increasing the osmotic pressure but no more than 2% per day until the normal level is reached. This should be about 1.025. If the fish is doing well, congratulations! If the fish seems to become stressed again, reduce the salt level once more but in increments of no more than 2% per day. You will notice that during this period of lower osmotic pressure, some corals will not open well. But, they will function properly again once balance is reintroduced.

An additional reason for maintaining a lower osmotic pressure before introducing a new fish is due to the conditions at retailers. Stores generally keep their salt level at 1.018 to keep the fish healthy by reducing disease. This salt level can also be maintained in a quarantine tank. This way a fish can adjust to a new environment before being added to the main aquarium. Since fish release pathogens during high levels of stress, using a quarantine tank is highly suggested. Pathogens can lead to disease in other fish.

When the new fish is just about ready to join the crew, begin adjusting the salt and pH levels as well as the temperature to that of the main aquarium. Remember not to exceed a 2% increase in the salt level per day. Once each tank has equivalent levels, you can easily scoop up the new fish and add him to his new family.

Fish that are sick or stressed can use a quarantine tank, but if one isn’t available, lowering the osmotic pressure in the main tank will do the trick to enhance their immune system. One additional option is the freshwater dip. This is accomplished by providing a freshwater alternative that has the same salt and pH levels as the aquarium. Place the fish in the fresh water for 10 minutes. This will take care of any pathogens and/or bacteria that may be affecting the fish. And while it will be rough for the fish to deal with, the dip should not kill it. If the fish passes on, it most likely did not have a strong enough immune system to survive for much longer anyway. The fresh water dip may be repeated each day if needed. Each of the suggestions in this article can and should be used to maintain fish health even after the aquarium is all set up. Happy Swimming!

Good luck and enjoy.
Paul Talbot