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Brackish Water Fish

Brackish Water Fish Care Sheet

Developed with and approved by a qualified veterinarian.

brackish water fish care sheet

This care sheet covers a variety of brackish water species, including:

  • Archerfish
  • Puffers
  • Scats
  • Monos
  • Leaf fish
  • Bumblebee goby
  • Dragon goby
  • Freshwater flounder
  • Mudskipper



Scientific names: Toxotes jaculatrix, Tetradon sp, Scatophagus argus, Monodactylus sebae, Monocirrhus polyacanthus, Brachygobius doriae, Gobioides broussonnetii, Achirus sp, Periophthalmus sp.

In their natural environment, brackish water fish live where freshwater meets saltwater in mangrove habitats, estuaries, marshes, lakes and seas. In aquariums, a lower specific gravity of saltwater is used to recreate this environment. Several brackish water fish species start out in brackish water environments and may transition to full saltwater as adults.


Typical appearance and behavior

  • Archerfish can jump out of the water or spit water to catch insects
  • Brackish puffers are similar to saltwater puffers in appearance, however, most species are smaller than their saltwater cousins
  • Scats have venomous dorsal and ventral spines
  • Monos have a unique diamond-shaped body
  • Mudskippers have the unique ability to survive out of water for periods of time



Care Difficulty Intermediate to advanced, depending on the species
Average Life Span Depends on species
Average Adult Size Depends on species
Diet Omnivore and carnivore, depending on the species
Minimum Habitat Size 10+ gallons, depending on species
Water Temperature 72-82°F
Specific gravity 1.005-1.015




Habitat size

Keep in an appropriate size aquarium for the species selected, which can range from 10 gallons for smaller species, like the bumblebee goby, to a much larger aquarium for a species like an adult dragon goby. 


Building your habitat

Water health -

  • Provide proper filtration to ensure optimal water quality to help maintain health. Slow to moderate water circulation should be provided to mimic water currents and high oxygen levels found in the brackish water fish’s natural habitat. Stable water quality (pH, ammonia, nitrate, nitrite) and water temperature are critical to the health of aquatic life. If you are unsure of your water quality, bring a sample to Petco for free testing.
  • An aquatic heater should be used to stabilize water temperature, ensuring it does not fluctuate more than 2 degrees in either direction in a 24-hour period
  • Brackish water fish need a specific gravity between 1.005 and 1.015, depending on the species. Always research your species-specific needs before adding aquarium salt. Do not allow specific gravity to fluctuate more than 0.001 in either direction in a 24-hour period

Décor- Provide plenty of space for swimming as well as plants, rocks or décor for hiding



A well-balanced brackish water fish diet consists of:

  • Live or frozen foods such as brine shrimp, bloodworms or blackworms
  • Flakes, pellets and freeze-dried foods or vegetable matter
  • Some brackish water fish are scavengers and will eat any leftover food or debris


Things to remember when feeding your brackish water fish:

  • Depending on the species, feed small amounts up to three times a day, no more than fish will eat in 1 to 2 minutes
  • Thaw frozen food before feeding


Brackish water fish care

Maintaining great water quality with regular water changes and adequate filtration is important to help keep your brackish water fish healthy

  • Daily: Check filter, water temperature and other equipment
  • Weekly: Test water quality at least once a week
  • Weekly to monthly: Change 10 to 25% of the total volume of water every two to four weeks or as needed; change filter media monthly

Avoid overcrowded conditions, which are a major cause of stress and disease


Where to buy brackish water fish

Various brackish water fish are available for purchase at your local Petco Pet Care Center; availability varies by location. Please call ahead to check availability.





Tank mates

  • Compatibility will vary by species being kept
  • May be compatible with some species of invertebrates or crustaceans



Signs of a healthy fish

  • Clear eyes
  • Healthy appetite
  • Bright, even coloring
  • Clean in appearance
  • Free of parasites or disease


Red flags (If you notice any of these signs, contact your local aquatic specialist or aquatic veterinarian.)

  • Loss of appetite
  • Spots or fungus on body or mouth
  • Listlessness
  • Labored breathing
  • Weight loss
  • Bloating
  • Cloudy eyes or pop-eye
  • Erratic swimming


Common health issues

Health Issue Symptoms or Causes Suggested Action
Health IssueFin rot Symptoms or CausesFrayed or disintegrating fins; the base of the fins usually reddens. Suggested ActionImprove water quality; consult your local aquatic specialist or aquatic veterinarian for treatment.
Health IssueIch Symptoms or CausesWhite spots appear on fins and body; fish rubs against hard objects or swims erratically. Suggested ActionTreat entire aquarium with a commercial parasite remedy and improve water quality; freshwater or saltwater (depending on specific gravity being kept at) dips can help dislodge the parasites; consult your local aquatic specialist or aquatic veterinarian for treatment.
Health IssueFungus Symptoms or CausesWhite, cottony growth and/or discoloration of the eyes. Suggested ActionQuarantine fish; use a commercial antifungal remedy as directed; consult your local aquatic specialist or aquatic veterinarian for treatment.
Health IssueBacterial infections Symptoms or CausesCloudy eyes, open sores and/or reddening of the skin. Suggested ActionImprove water quality; add freshwater aquarium salt; use a commercial antibacterial remedy as directed; consult your local aquatic specialist or aquatic veterinarian for treatment
Health IssueCottonmouth or columnaris Symptoms or CausesCottony white growths along the body and/or gills, frayed fins and gills turn brown and necrotic in late stages; caused by bacterial infection. Suggested ActionQuarantine fish; improve water quality; lower aquarium temperature to 72°F to deter bacteria from growing; medicate as directed; consult your local aquatic specialist or aquatic veterinarian for treatment.
Health IssueViral infection (lymphocystis) Symptoms or CausesWhite nodule growths on fins or body. Suggested ActionImprove water quality; consult your local aquatic specialist or aquatic veterinarian for treatment.



  • How to make brackish water? Brackish water is made by mixing a synthetic sea salt mixture with freshwater, bringing the specific gravity to a level of 1.005 to 1.0015 depending on the species.
  • What fish live in brackish water? There are a variety of fish species that can live in brackish environments, including archerfish, monos, scats and bumblebee gobies.
  • Can betta fish live in brackish water? The species betta splendens does not live in brackish water environments.
  • Can saltwater fish live in brackish water? There are some species of fish that can transition from saltwater to brackish and vice versa, but most species of saltwater fish will not thrive in a brackish water environment.


Additional care sheets

Notes and resources

Ask a Pet Care Center associate about Petco's selection of products available for the care and happiness of your new pet. All products carry a 100% money-back guarantee.

Because all aquatic life are potential carriers of infectious diseases, such as atypical mycobacterium and salmonella, always wash your hands before and after handling your aquatic life and/or habitat contents to help prevent the potential spread of diseases.

Pregnant women, children under the age of 5, senior citizens and people with weakened immune systems should contact their physician before purchasing and/or caring for aquatic life and should consider not having aquatic life as a pet.

Go to the Centers for Disease Control at for more information about aquatic life and disease.


The information on this Care Sheet is not a substitute for veterinary care. If you need additional information, please contact your veterinarian as appropriate.