A brackish environment occurs where freshwater and saltwater meet. A brackish aquarium is installed in the same way as fresh and saltwater tanks.
Since a freshwater tank is easily converted to brackish with the addition of sea salt and equipment such as a protein skimmer, maintaining a brackish tank is often a transition project for a hobbyist.
By definition, a brackish environment is highly variable. Lagoons, coastal streams, mangroves swamps, and estuaries change with rising and falling tides.
Their chemistry is affected by the amount of rain they receive, by the temperature in the region and by the degree of evaporation to which they are subjected.
It is very difficult to come up with a single definition for brackish water, but there are three brackish habitats or biotopes:
- Estuary
- River
- Mangrove/swamp
The species that live in these environments are classified as:
- Low salinity
- Medium salinity
- High salinity
But even these distinctions are not necessarily fixed, with most species showing tolerance to change and a high level of adaptability. In general, however:
- Low salinity species live in water. with 1,002 to 1,005 sg.
- The medium salinity species inhabit 1,008 to 1,025 sg (complete seawater).
- High salinity species live with the full strength of seawater and will not thrive below 1,012 sg.
The Estuary
This is the most commonly replicated biotype for an aquarium.
Estuaries have higher and more constant salinity than other brackish environments because in nature they are found in the mouths of large rivers very close to the ocean.
Tanks balanced to follow this model are easier to maintain. They only require slow to moderate water flow and good aeration to keep the pH and specific gravity levels within the correct parameters.
An added bonus for the hobbyist interested in keeping sharks is that the minimum recommended size for an estuary-based brackish tank is 55 gallons (208.19 liters).
(This is an ideal environment for the Colombian shark catfish that is described at the end of this article.)
The specific objectives for an estuary tank are:
- 78-84 ° F (25.5-28.8 ° C)
- pH 7.6 – 8.5
- Salinity 1,010 to 1,025
The rocks and clean driftwood with good branching provide perfect decorative elements and hiding places for tank dwellers.
The Brackish River
Specific gravity is generally not as high in a brackish river, nor is it as stable. Brackish rivers tend to be highly oxygenated because they flow rapidly, with strong plant growth on the sides of the canal.
In a tank assembly, a powerhead will be necessary to move the water, and sufficient aeration is required to keep pH and SG levels within good standards.
For some aquarists, this is an ideal test of a brackish setup because it can be accomplished in tanks as small as 10 gallons (37.85 liters) and up to 75 gallons (283.9 liters).
In these tanks you are trying to achieve:
- 78-84 ° F (25.5-28.8 ° C)
- pH 7.6 – 8.5
- Salinity 1,005 to 1,010
Expect to use heavy plantations on the sides and in the water, with driftwood and rocks in the background.
Mangrove Swamp
Located along estuaries and rivers, mangroves have low water levels and little movement, resulting in a mid to high range salinity level.
Most mangrove tanks are 20 gallons (75.7 liters) or larger.
In addition to fish, crabs and mudskippers are often present.
These tanks tend to be long and shallow, rather than tall and deep.
Mangroves, which are excellent for exporting nutrients, can be used as the main filter in these tanks.
The specific parameters to achieve are:
- 78-84 ° F (25.5-28.8 ° C)
- PH 7.8 – 8.5
- Salinity 1,010 to 1,015
You will need mangroves, floating plants, rocks, and driftwood or swamps at the bottom.
Required Equipment
Beyond the tank itself, you will need typical freshwater aquarium equipment including:
- Sufficient filters to turn the water at least 10 times per hour.
- A heater rated for use of fresh and saltwater.
- Plants that will grow in saltwater and appropriate for the biotope you are creating.
- The substrate, typically somewhat sandy for this type of tank.
- Marine salt.
- Test kits that handle fresh and saltwater tests.
You will need to perform pH and KH tests with a saltwater kit, and all other tests with a freshwater kit.
Mixing Brackish Water
In the water mixture for a brackish tank:
- 1,025 sg of water contains approximately 4.7 ounces of sea salt per gallon
- 1,010 sg of water contains approximately 2.0 ounces of sea salt per gallon
One of the keys to achieving a brackish state in a tank is to mix the water in a bucket and reach the desired salinity before adding it to the tank. Remember, you can add more salt, but you can’t get it out of the water once it’s mixed.
The good news, however, is that brackish fish do not require exact salinity. It is this very tolerance for a margin of error that draws many people to brackish aquaculture, especially those who are intimidated by the demands of a full tank of saltwater.
Populating Your Brackish Tank
After your tank has been properly cycled, you’ll need to select species based on the salinity level you’re maintaining:
- Low salinity species include fish like the Orange and Green Chromides, Pike Livebearers, Knight Gobies, and Figure-8 Pufferfish.
- Medium salinity fish include droppings, Violet gobies, some archerfish, monos, and the Colombian shark catfish
- High salinity species include dog-faced puffers, milk spot blowers, and snappers.
Popular Sharks For Brackish Aquarium
While many reports of aquarists successfully keep saltwater shark fish in brackish estuary tanks, initially, maintaining some form of shark catfish offers the best chance of success.
Australian Shark Catfish
The Australian shark catfish reaches a maximum length of 19.7 inches (50 cm). It does well with fish of the same size or larger and likes lots of driftwood and rocks to hide in.
This is an active species, which needs a lot of space to swim. It is generally dark gray with a bluish tint and a white underside. It accepts a wide variety of prepared and live foods, making it an easy species to feed.
- Ideal conditions are 62.6-80.6 ° F / 17.0-27.0 ° C, pH 6.4-8.0.
Berney Shark Catfish
The Berney shark catfish reaches a maximum length of 15 inches (31.1 cm). It also requires tankmates of equal or greater size and likes many hiding places.
An active swimmer, Berney’s Shark is not a finicky eater. It is a silver to bronze fish that appears to be generally dark gray in color, with a paler belly.
- Ideal conditions are 68-82 ° F / 20.0-28.0 ° C, pH 6.5-8.0.
Columbian Shark Catfish
The Columbian Shark Catfish is a perfect tankmate for this type of setup. It is a peaceful creature with new special needs. It reaches a manageable size of 10 “(25.4 cm) when fully developed.
Although it will eat smaller species, it tends to get along with fish of comparable size, especially if there are many rocks and plants in the aquarium.
- Ideal water conditions are 74-79 ° F / 23.3-26.1 ° C, pH 7.0-7.5.