The world of Brackish Water aquariums is one I have recently begun to explore. I was motivated by the selection of interesting fish I saw at my local fish store and a desire to learn more about the magnificent aquatic ecosystems where streams and rivers meet the sea. It seemed a bit daunting at first with so much conflicting information on the Internet, and I began to get discouraged.

“Yes you can keep plants” vs “No you cant have plants”. “1 tablespoon of salt does 10 gallons” vs “10 tbs per gallon”! But then I came across an article that outlined three distinct zones within a typical natural Brackish Water ecosystem. The Polyhaline Zone being closest to the open ocean, Mesohaline Zone where the two waters mixed in more even concentrations, and the Oligohaline Zone where Saltwater penetrated upstream into a Freshwater ecosystem through tidal actions. The definition of these three zones allowed me to get an understanding of why there were varying salinities suggested for Brackish fish and why some people can keep plants in Brackish water.

The Polyhaline Zone:

Closely resembles a marine environment and is frequented by many marine species. Vascular plants will not grow here. It has a suggested salinity near that of the open ocean, around 10 tbs of marine salt per gallon of water.

The Mesohaline Zone:
Represents a much more even mix of Saltwater and Freshwater. This can be reached with around 5 tbs of marine salt per gallon of water. It is very typical of Brackish systems I find at my local aquarium store. It is not very friendly to vascular plants but you might be able to get a few to survive if you are lucky.

The Oligohaline Zone:
Has a very low salinity and will accept a wider range of vascular plants. I grow Java Fern, Java Moss, Hornwort, Vallisneria and a Cryptocoryne in my low teck Oligohaline tank. Salinity here can be archived with 1-2 tbs per gallon of water.


Plants suitable for the Oligohaline zone


The second concept I find helpful in understanding Brackish Water Aquariums is Eurohaline. This applies to the livestock suitable for Brackish water. Fish that have evolved to become Eruohaline have an ability to survive in changing salinity levels. Many fish and Invertebrates have this biological skill and it allows them to live in Estuaries, Mangrove Swamps and Salt Marshes around the world. The salinity of such places can change due to ocean tides, rain patterns and changes in seasonal water levels. Many aquatic creatures have adapted to compensate for those changes.

Diversity can renew your interest

Understanding where the fish you want to keep come from, and what type of ecosystem that represents are crucial in successfully keeping a brackish tank. You will also want to learn about how some of these fish make use of the different zones as they mature and what changes they will require as they get older. Think of the common Salmon that we are all so familiar with. Salmon are Eurohaline and breed in Freshwater streams, migrating out the ocean to mature. Some of the Brackish Water fish available to as hobbyists also have similar requirements.

A perfect inhabitant

Another great choice

If you provide the right conditions, a brackish tank will provide you with an interesting and diverse home aquarium. I hope these few bits of terminology can help you to more fully understanding the world of Brackish Aquariums and enhance your chances of success with the beautiful creatures that live in them.

Brackish Water Aquariums. Understanding is the key.
By: Ken Tweddle
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