Brackish Fish Species

Brackish fish, also known as brackishwater fish or brackish water fish, originate from areas in which freshwater meets saltwater. Fish that live in these areas are able to tolerate a wide range of salinities. In nature, there are three kinds of brackish water ecosystems.

The Polyhaline Zone:

The Polyhaline Zone is closest to the open ocean. It 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 tbsp of marine salt per gallon of water.

The Mesohaline Zone:

The Mesohaline Zone is where the two waters mix in more even concentrations and 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 at many aquarium stores. 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:

The Oligohaline Zone is where saltwater penetrates upstream into a Freshwater ecosystem through tidal actions. It has a very low salinity and will accept a wider range of vascular plants such as Java Fern, Java Moss, Hornwort, Vallisneria and Cryptocoryn. Although plants specifically adapted to brackish water environments are not at all common in the trade, mangrove seedlings are becoming increasingly available. Certain aquatic plants that are usually grown in freshwater aquariums may also survive in mildly saline waters.

In general, the freshwater plants that fare best are those with waxy leaf coverings, such as the various grasses of the genus Vallisneria, the giant sagittaria, Sagittaria gigantea, and Java moss, Microsorium pterops. You might also wish to experiment with various marine algae. Salinity in this ecosystem can be achieved with 1-2 tbsp of marine salt per gallon of water.

There are several biological terms that are used when discussing brackish water fish:

Eruohaline species have an ability to survive in changing salinity.

Euryhaline species easily move between fresh and salt water but not necessarily on purpose or with regularity. 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.

An example of a euryhaline species is the bull shark, which lives in Lake Nicaragua of Central America and the Zambezi River of Africa. Both these habitats are fresh water, yet bull sharks will also migrate to and from the ocean. Specifically, Lake Nicaragua bull sharks migrate to the Atlantic Ocean and Zambezi bull sharks migrate to the Indian Ocean. More and more sharks are being found in the Mississippi River in the United States, up to several hundred miles from the sea.

Anadromous fish spend most of their lives feeding in the open ocean, but migrate to spawn in freshwater

Anadromous fish, like the salmon, are born in and spend the juvenile part of their lives in freshwater, but moves to saltwater in the mature stages of its life for two to six years, then returns to freshwater to spawn where it was born and dies soon after breeding.

Amphidromous fish also move between saltwater and freshwater

Amphidromous fish move between fresh water and salt water during some part of their life cycles, but not for breeding. The migratrion occurs regularly at some other stage of the life cycle.

Catadromous creatures breed in the ocean but live most of their lives in fresh water

Catadromous species migrate from fresh water into the ocean to breed in the sea. Catadromous fish are freshwater eels of the genus Anguilla, whose larvae drift on the open ocean, sometimes for months or years, before traveling thousands of kilometers back to their original streams to live out the rest of their lives in fresh water until they are mature and ready to breed.

Diadromous fish travel between freshwater and the sea on a regular basis

Diadromous fish are truly migratory fish. They travel between freshwater or brackish water and the sea. There has been no English term by which one can refer collectively and briefly to anadromous, catadromous and other fishes which truly migrate between fresh and salt water, and this new term is now used to refer to them collectively without distinquishing the exact life phase or reason why they migrate.

Understanding where the fish you want to keep come from, and what type of ecosystem that represents are crucial to 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.

Introduce brackish water fish to your tank slowly

Most pet stores maintain brackish water fish in either freshwater or saltwater, depending upon the species. Orange chromides are, for example, usually kept in freshwater aquariums, while monos are often exhibited with marine fish. Although they will survive under these conditions, most will not exhibit normal behavior or attain their brightest coloration.

You should take note of how the fish that you purchase have been maintained, as the salinity and pH in your own brackish water aquarium will likely be very different. Even though most estuarine species are quite hardy, you should err on the side of caution and introduce them slowly into your aquarium.

Brackish fish, in general, do best in water with a salinity of 1.015, or 1/4 cup marine salt per gallon, and a pH of 7.5 to 8.4. Estuarine fish generally fare well at a pH of 7.6.

Most brackish water fish are extremely active animals and, consequently, require highly oxygenated water. When setting up your filtration system, be certain that the water returned to your aquarium activates the surface well, or add additional air stones.

Brackish water fish and invertebrates experience daily changes in salinity, water level, and pH in the wild. These animals are, therefore, often quite resilient captives and some of these creatures actually benefit from salinity fluctuations. While few brackish water animals regularly breed in home aquariums, it does seem likely that such fluctuations might be necessary to stimulate reproductive behavior.

Although many estuarine animals can tolerate marine water, the most commonly kept species spend most of their time in water that is considerably less saline. The safest salinity level is approximately 1.005 to 1.015, which is roughly equivalent to 1 gallon of seawater dissolved in 4 gallons of freshwater.