There is more to the aquarium world than just saltwater and freshwater. Did you know that some fish species naturally inhabit areas where rivers meet the ocean and the water is not quite freshwater and not quite saltwater either? These environments are known as brackish areas and house some very special fish species!
If you want to keep a system that is between fresh and saltwater, then a brackish water system would be perfect. Keep reading for 6 fascinating brackish water fish species that are sure to brighten up any brackish water tank!
Bumblebee goby (Brachygobius sp.)
If you’re interested in setting up a brackish aquarium but don’t have a lot of space, bumblebee gobies might be the right brackish water fish for you. This species grows to a maximum size of 1.6 inches (4 cm), which means they don’t need a large tank. In fact, a 16 inch (40 cm) setup should be enough for a group. Keep in mind that these are bottom-dwelling fish, so a long tank is better than a tall one.
Keep your bumblebee gobies in groups of 6 or more in low-grade brackish water. A single species setup works best in most cases, as these fish are easily outcompeted for food and intimidated by larger and more assertive fish. Provide plenty of hiding places with tubes, plants, rocks, and driftwood. Keep in mind that bumblebee gobies can be a little difficult during feeding time and some don’t accept anything but live food. Grindal worms are easy to culture and will definitely be appreciated.
You can find a full bumblebee goby care sheet on Aquariadise here.
Figure 8 pufferfish (Tetraodon biocellatus)
If you like to fish with a bit of personality and are an experienced fishkeeper and don’t mind setting up a brackish water single species tank, then keep reading. Figure 8 puffers are one of the smaller pufferfish species and can be kept in aquariums of at least 31.5 inches (80 cm). They are easier to keep than most other puffers but are still not the best fish for beginners due to their aggressive nature and specific diet, which should consist of almost 100% mollusks.
Keep your figure 8 puffer alone or with quick, short-finned fish. Salinity should be at least 1.005 and plenty of places to explore are a must to prevent boredom. Try adding all sorts of decorations and plants; Java fern is easy to grow and shouldn’t mind the salt. Feed crunchy foods like snails, mussels, and crab legs to wear down the puffer’s ever-growing teeth.
You can find a full figure 8 pufferfish care sheet on Aquariadise here.
Four-eyed fish (Anableps sp.)
Although four-eyed livebearing fish from the Anableps genus is one of the “classic” brackish water fish species, they are not the easiest fish to keep. This is mostly due to their size: Anableps anableps females can grow to an impressive 12 inches (30 cm). Combine this with the fact that these fish naturally live in very large groups and you’re looking at quite the setup; anything smaller than 60 inches (150 cm) is out of the question. These brackish water fish also do best in groups of at least 6.
Water salinity isn’t too much of an issue as long as it’s brackish but can be closer to freshwater levels. Don’t fill the tank all the way to the top and consider providing some shallow or land areas with faux mangrove roots to imitate their natural habitat. Feed an insect-based diet. Peaceful tankmates are a must, as these fish aren’t the best at defending themselves.
All in all, I wouldn’t recommend these brackish fish to inexperienced hobbyists. Do your research and don’t ignore the tank size guidelines!
Molly fish (Poecilia sphenops)
Mollies and other livebearers (like swordtails and guppies) are popular among freshwater fishkeepers, but did you know they can also tolerate salinity up to full saltwater? This makes them a great choice for anyone looking to bring some life and color into their brackish water tank.
Keep short-finned mollies in an aquarium of at least 35 inches (90 cm) to give them plenty of water to swim in. Go for at least 1 male and 2 to 3 females; more is always better as these fish love the company of their own species. Other tankmates should be chosen with care, as mollies are known to be a little nippy. Feed a varied diet consisting of herbivore pellets, algae tablets, frozen foods, and freshly blanched vegetables.
Keep in mind that, like other livebearers, mollies breed very quickly. Some brackish fish enthusiasts like to keep their mollies with tankmates that have an appetite for baby fish, others prefer selling or giving away excess fish to other hobbyists.
You can find a full molly fish care sheet on Aquariadise here.
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Violet goby/dragon goby (Gobioides broussonnetii)
Want a totally bizarre, prehistoric-looking, dragon-like brackish water fish? Look no further! Violet gobies are as weird as it gets, which has made them gain significant popularity over the past few years. Unfortunately, many aquarists still keep them in freshwater community tanks, which is not an ideal situation. This species actually needs low to medium salinity (at least 1.005) and doesn’t do well with most tankmates.
To keep a single fish, a 48 inch (120 cm) aquarium is needed. Bottom space is more important than water volume, as these brackish fish are bottom feeders. This also means a sand substrate is needed so that your goby can properly burrow and forage.
Avoid aggressive and/or active fish species as tankmates. Contrary to what their scary face suggests, violet gobies are not carnivorous fish, so livebearing fish, like mollies, should be safe in their company. Feed a varied diet consisting of frozen foods, live foods, and plant-based foods like algae pellets.
They might be a little scary at first, but they definitely grow on you!
Wrestling halfbeak (Dermogenys pusilla)
The appropriately named wrestling halfbeak is a rather strange-looking fish: its upper jaw is only about half the size of its lower jaw. Although it’s not strictly a brackish water fish (hard and alkaline freshwater is also acceptable) it can be kept in a brackish water tank with a salinity up to 1.005. Keep groups of at least 5 in a 31.5 inch (80 cm) aquarium.
If you’re interested in setting up a brackish water tank for these fish, keep in mind that they’re a little clumsy and shy. They appreciate a densely planted tank and are easily spooked. A scared halfbeak might end up swimming into the tank panels and damaging its jaw, so be careful with sudden changes, like quickly turning off the lights. Jumping can also be a problem; don’t keep these brackish fish in an aquarium without a lid!
Wrestling halfbeaks are surface dwellers, which means floating foods are easiest. Fruit flies and other small floating pellets are good, but keep in mind that the latter might not be accepted at first.
These fish are definitely weird and will make you forget about popular freshwater fish!
Bonus invertebrate: red claw crab (Perisesarma bidens)
Interested in setting up a brackish paludarium tank instead of a regular aquarium? Red claw crabs are often sold as fully aquatic freshwater crabs but actually do better in slightly brackish water; it is definitely not hard to learn how to make brackish water if you’ve made this mistake. They also need access to land; a 50:50 ratio of land to brackish water should work well. Without land and salt, your red claw crabs won’t live long.
A group of 3 red claw crabs (1 male, 2 females) can be kept in a paludarium of at least 23.5 inches (60 cm). The land area should be sandy and contain multiple hiding places, as crabs are vulnerable and want to hide during molting. Be sure to seal any escape routes, because these crabs are true escape artists and will try to crawl through even the smallest hole! Feed a diet consisting of both meaty and plant-based foods like frozen foods, invertebrate pellets like Crab Cuisine, and fresh blanched veggies such as peas.
You can find a full red claw crab care sheet on Aquariadise here.
Most popular freshwater aquarium plants struggle with even a little bit of salt and will perish in brackish water setups. Luckily, there are still some options, especially for low-end brackish levels. You can find a list of aquarium plants that tolerate brackish water here!
If you have any more questions about keeping brackish water fish, brackish water conditions, or if you want to share your own experiences with any of these species, don’t hesitate to leave a comment below!