The key to mastering your marine environment is understanding the effects of your osmoregulation system within your saltwater aquarium. One of the little mentioned issues in saltwater aquarium keeping is facilitating the saltwater fish’s osmoregulation system.

Osmoregulation systems maintain a balance of salts and fluids inside your saltwater fish. The greater amount of salt within the water makes the osmoregulation system work harder to correct the salt levels and minerals inside the fish creating higher osmotic pressure. A fish can tolerate different saltwater levels depending on the environment the fish has evolved from.

Freshwater fish can only handle very low osmotic pressure compared to saltwater fish which are used to withstanding a higher level. Freshwater fish will only handle low osmotic pressure in comparison to saltwater fish as saltwater fish have evolved to withstand higher levels.

There are some fish that tolerate considerable changes in osmotic pressure and salt levels.  This allows them to travel from freshwater rivers all the way to saltwater oceans!  Fish that live in saltwater and freshwater are named brackish water fish.  Though there are many saltwater fish that venture into fresh water throughout their lives at specific periods.

A fresh water fish generally maintains its internal salt level higher than that of the surrounding water. In most cases fresh water fish maintain their internal salt levels higher than the surrounding waters. Their gills absorb salt and oxygen from their environment.  A Large amount of water is constantly being diffused into fresh water fish.  It’s then excreted as urine making sure it’s system is continually being flushed out.

In contrast, a saltwater fish keeps an internal salt level lower than its surrounding waters.  The osmotic pressure will then pull water from the fish and push the salt in. As a consequence to maintain correct salt levels, the saltwater fish need to excrete salt from its gills.  A saltwater fish in water that has a slightly higher level of salt will direct its molecular energy to osmoregulation.  Hence if the fish begins to suffer from stress, decreasing the salt levels heeds in the recovery of the fish.

Beginning to lower saltwater levels reduces osmotic pressure in the fish which allows the fish to allocate more molecular energy towards the fishes immune system.  This helps the stressed fish from becoming ill and can also be used as a treatment for fish that are already sick.

The ocean remains the most stable ecosystem. It occupies 77 percent of the earth’s surface it also experience very little fluctuations in salt levels compared to small rivers and freshwater lakes.  Most Saltwater Fish only handle around 2 degrees salt change a day. E.g. 1.023 to 1.025.  Having an Understanding of the osmoregulation system will help protect your home aquarium.  All fish you introtroduce to your aquarium will be stressed initially and it usually takes around 3 weeks for a fish to settle into it’s new environment and have it’s stress levels begin to return to it’s its natural healthy levels. It’s advisable in this time frame to lower the salt levels of your aquarium water to around 1.018.  This will decrease the osmotic pressure which the fish incur.  You will then gradually increase your level to it’s previous level.  But always remember to never lower nor raise your salt levels more than 0.002 per day!
With that in mind you need to prepare your tank a few days prior to introducing your new fish so the salt levels are correct when brining your new fish home.  When the fish seem to be doing ok over a few weeks you can start slowly returning your salt levels to 1.025.  At any time you notice the fish appear to be stressed, it may be worth reducing it to 1.018 once again.

Some people may notice their corals may not like the lower salt levels and may not appear to open up during this time.  This is nothing to worry about and will not cause any long term harm or problems.
 

For a professional guide on Saltwater Aquariums check out http://www.exclusivefishfilms.com
 

Paul Talbot