There is more to the aquarium world than just freshwater and marine. Did you know that some fish naturally inhabit areas where rivers meet the sea and the waters are not quite fresh but not quite marine either? They offer a great opportunity to set up a brackish aquarium, which is actually not as difficult as some might think.
Keep reading for six fascinating brackish water fish that are sure to brighten up any brackish tank!
Bumblebee goby (Brachygobius spp.)
If you’re interested in setting up a brackish aquarium but don’t have a lot of space, bumblebee gobies might be the right fish for you. These gobies grow to a maximum size of around 1.6″/4cm, which means they don’t need a large tank. In fact, a 16″/40cm setup should be enough to sustain a group. Keep in mind that these are bottom dwellers, so a long tank is always 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 tankmates. Provide plenty of hiding places: tubes, plants, rocks and driftwood all work well. Keep in mind that bumblebee gobies can be a little difficult during feeding time and some don’t accept anything but live foods. Be sure to have some kind of live food colony set up for them if you want to see their natural behavior! Grindal worms are easy to culture and will definitely be appreciated.
You can find a full bumblebee goby caresheet on Aquariadise here.
Figure 8 pufferfish (Tetraodon biocellatus)
If you like fish with a bit of personality, are an experienced fishkeeper and don’t mind setting up a brackish single-species tank, keep reading. Figure 8 puffers are one of the smaller pufferfish species and can be kept in aquariums of at least around 31.5″/80cm. They are easier to keep than most other puffers but unfortunately still not the best choice for beginners due to their aggressive nature and specific diet, which should consist almost 100% of molluscs.
Keep your figure 8 puffer alone or with quick, short-finned tankmates. 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 caresheet on Aquariadise here.
Four-eyed fish (Anableps sp.)
Although four-eyed livebearing fish from the Anableps genus are one of the “classic” brackish species they are not the easiest to keep. This is mostly due to their size: Anableps anableps females can grow to an impressive 12″/30cm. Combine this with the fact that these fish naturally live in very large groups and you’re looking at quite the aquarium. Anything smaller than 60″/150cm is out of the question and the bigger the better. Surface area is obviously the most important thing here, as Anableps spend much of their time using their second set of eyes to keep an eye on whatever is going on above the surface. Go for at least 6 fish.
Water salinity isn’t too much of an issue as long as it’s brackish: low- to mid-end should work well. 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 the 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 Anableps to unexperienced fishkeepers. 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 a salinity up to full marine? This makes them a great choice for anyone looking to bring some life and color into their brackish tank.
Keep short-finned mollies in an aquarium of at least 35″/90cm to give them plenty of space to swim. Go for at least one male and two females; more is always better, 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 even fresh blanched vegetables.
Keep in mind that, like other livebearers, mollies breed very quickly. A plan B in case of overcrowding is in order! Some aquarists 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 caresheet on Aquariadise here.
Violet goby/dragon goby (Gobioides broussonnetii)
Want a totally bizarre, prehistoric looking, dragon-like fish for your brackish aquarium? 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 at all. These gobies actually need low to medium salinity (at least 1.005) and don’t do well with most tankmates.
To keep a single violet goby an aquarium of at least 48″/120cm is needed. Bottom space is more important than volume, as these fish are bottom feeders. This also means a sand substrate is needed for the fish to be able to properly burrow and forage. Avoid tankmates unless they’re peaceful. Contrary to what their scary face suggests violet gobies are not carnivorous fish, so livebearers like mollies should be safe in their company while larger and more aggressive fish can really stress them out. Feed a varied diet consisting of frozen and live foods as well as plant-based stuff like algae pellets.
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 fresh water is also acceptable) it can be maintained in brackish tanks with a salinity up to 1.005. Keep it in groups of at least 5 in an aquarium of at least around 31.5″/80cm.
If you’re interested in setting up a wrestling halfbeak tank keep in mind that these fish can be 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 things like suddenly turning off the lights. Jumping can also be a problem – don’t keep these fish in an aquarium without a lid!
Wrestling halfbeaks are surface dwellers, which means floating foods are easiest. Fruit flies and small floating pellets are good, but keep in mind the latter might not be accepted at first if the fish aren’t used to it yet.
Bonus invertebrate: Red claw crab (Perisesarma bidens)
Interested in setting up a brackish paludarium instead of a regular aquarium? Red claw crabs are often sold as fully aquatic freshwater crabs but actually need a salinity of around 1.005. They also need access to land – a 50/50 ratio of land and water should work well. Without land and salt your red claw crabs won’t live a long life.
A group of 3 red claw crabs (1 male, 2 females) can be kept in a paludarium of at least around 23.5″/cm. The land area should be sandy and contain multiple hiding places, as crabs are vulnerable and want to hide during molting. Coconut hides should work well. 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 caresheet on Aquariadise here.
Note: there are various red clawed crabs out there and taxonomy/naming might be confusing. Perisesarma bidens is the most common but as can be seen in the video below there are some other crabs from the (Peri)sesarma genus out there.
Most popular aquarium plants struggle with even a little bit of salt and will perish in brackish setups. Luckily there are still some options, especially for low-end brackish. You can find a list of aquarium plants that tolerate brackish water here!
If you have any more questions about keeping these brackish aquarium fish or if you want to share your own experiences, don’t hesitate to leave a comment below!