Related FAQs: Brackish Aquariums In General, FAQs on Brackish Salty Water, Related Articles: Big But Beautiful: A Southeast Asian Estuary by Neale Monks, Brackish Aquarium Keeping in General, Brackish System Components and Set-Up, Brackish Livestock Groups, Brackish System Maintenance, Brackish for Beginners, 1:  Small Species For the Small  Aquarium: A South Asian Coastal Stream
© Neale Monks

Brackish water fish faunas generally contain two components, freshwater fishes that have adapted to salty water, and marine fishes that have adapted to water with less salt than seawater. In South Asia, the freshwater fish families that have moved from rivers and streams into brackish water environments include Bagrid catfish, cichlids, and cyprinids, killifish, and spiny eels. Going in the other direction, the marine fishes that have become adapted to life in brackish water include the glassfish, gobies, halfbeaks, pufferfish, and soles. Many of these fishes are also found in Southeast Asia as well. But there is another level of complexity to the South Asia brackish water fish fauna, and that is the way it mixes things from both Africa and Asia. The cichlids and killifish, for example, are both much more diverse in Africa than Asia, and are completely absent from Southeast Asia. The barbs and catfish, on the other hand, are closely related to species found right across Asia. All this makes an aquarium based on a South Asian coastal stream extremely interesting, mixing as it does fishes that might be described as African and Asian, marine and freshwater.

 

Water chemistry

The term brackish water actually covers a range of conditions rather than just one thing. Next month, we'll be looking at a completely different brackish water habitat, a Southeast Asian estuary, but this month the focus is on a coastal stream where the influence of the sea is very slight. The salinity in this aquarium will be around 6-9 g/l (0.8-1.2 oz/gal), or about 10-25% the salinity of normal seawater. Measuring salinity directly is difficult, so aquarists use a hydrometer to measure specific gravity instead, which in this case will be between SG 1.003 and 1.005. There are two types on the market, floating glass ones and plastic swing-arm ones. Floating glass ones are cheaper (around £5) but more fiddly to use, whereas the plastic ones are easy to use but more expensive (around £20). Whichever you use, be sure and read the supplied instructions; much of the supposed inaccuracy of hydrometers only comes about when they are used improperly. Apart from salinity, the other two parameters of interest are pH and hardness. For this aquarium aim for pH 7.2-7.5 and a moderate level of hardness.

 

Making up the brackish water

The single most important thing to remember about making up brackish water is to add salt to the bucket, not the aquarium. Brackish water is made using marine salt mix, not tonic salt or cooking salt. To start with, add about one level teaspoon per litre (or about four teaspoons per gallon). Stir the salt in thoroughly, and then let the water sit for twenty minutes to dissolve properly. Once you're happy the salt has fully dissolved, measure the specific gravity. Add more salt if the specific gravity is not high enough, or add more water if it is too low. It doesn't matter if the specific gravity is not exactly right, as brackish water fishes are inherently adaptable, but for this community you don't want the specific gravity to exceed 1.005. Don't forget to add dechlorinator!

 

Plants and decor

Because brackish waters tend to be silty, most of the plants growing in such places are emergent forms rather than submerse ones, that is, they stick their roots in the nutrient-rich mud but keep their leaves above the waterline. Mangroves, Nypa palms, and numerous reeds and sedges are classic examples. Nonetheless, there are some commonly traded aquarium plants that inhabit brackish waters in the wild and will do well in this aquarium. Concentrating on the species found in India or Sri Lanka, Java moss, Aponogeton crispus, Cryptocoryne ciliata, Cryptocoryne wendtii, and Hygrophila polysperma all thrive at SG 1.003. Java moss and Cryptocoryne ciliata will also do well at higher salinities as well, certainly at least SG 1.005. Java ferns are another very salt-tolerant species of aquarium plant, and though they aren't found in India or Sri Lanka, this might be overlooked in favour of their hardiness and reliability. One last thought: keeping plants in brackish water is stressing them in some ways, so it is important to get the other things'such as lighting, substrate quality, fertilisation, and carbon dioxide concentration'spot-on if you want them to thrive. Of the species mentioned here, the least demanding are probably Java ferns and Java moss, followed by Cryptocoryne wendtii.

The idea here is to create a stream containing a tangle of aquatic plants to represent the vegetation growing along the banks, but some open swimming space is important too. In terms of substrate, a mix of silica sand and fine pea gravel will nicely suggest the silty, muddy environment being modeled as well as providing some digging space for spiny eels and gobies. Try and include a mixture of shady and open areas. Cichlids and killifish tend to prefer the darker regions where they are safe from predators, whereas barbs and glassfish will spend much of their time swimming about in the open. Use slates and other dark rocks to shore up some sandbanks so that the aquarium has a more three-dimensional feel, and use bogwood to suggest the roots of mangroves and other trees. Bamboo canes can also be used to replicate thickets of reeds and sedges.

 

The South Asian fish fauna

One of the most celebrated South Asian brackish water fish is the dwarf cichlid Etroplus maculatus, commonly known as the orange Chromide. This small, brightly coloured fish is relatively peaceful by cichlid standards and presents few problems in the community tank. It does not dig, and while it will guard its territory as vigourously as any other cichlid, in a sufficiently roomy aquarium combines well with other community fish. Among the killifishes, a number of species of Aplocheilus are native to this region, of which the most commonly traded is the sparkling Panchax Aplocheilus lineatus. This species is quite big by killifish standards, getting to around 10 cm/4" in length, and also very predatory, happily eating fish as large as neon tetras in size. It is also quite territorial among its own kind. On the other hand, it is beautifully coloured and easily maintained, willingly eating all sorts of floating foods including flake. An artificial variety known as the Golden Wonder killifish is also available.

Barbs are surprisingly well represented in the brackish waters of South Asia, though mostly the larger species with limited usefulness in home aquaria. One species that is fairly small and widely traded is the Ticto barb Puntius Ticto. This species grows to about 10 cm/4" in length and does best kept in groups of six or more. Outside of breeding condition both males and females are rather plain, with silvery-brown bodies marked only with a couple of dark spots on each flank, but when sexually mature the males sport a thick red band running along the flank from eye to tail. Among the other brackish water barbs are the Blackspot barb Puntius vittatus (5 cm/2") and the greenstripe barb Puntius vittatus (18 cm/7"). None of the barbs appreciate strongly brackish water, but at SG 1.003 they will do very well indeed, providing plenty of interest and movement in the middle part of the tank. Another good choice for midwater activity is the Indian glassfish Parambassis ranga. These fish get to about 6 cm/2.5" in length and inhabit both fresh and brackish waters. In temperament they are much like robust tetras or barbs, doing a lot of chasing and displaying to one another but still best kept in groups of six or more. Glassfish do have a reputation for being finicky eaters, and it is certainly true they have no interest in flakes or pellets. But they do not need live foods every day, though providing them with some live brine shrimp or daphnia will certainly be appreciated. Frozen bloodworms, small pieces of prawn and mussel, and lobster eggs will all be greedily snapped up.

Turning to the fish that live closer to the substrate, catfish are of course pre-eminent. As with the barbs, most of the catfish in brackish waters tend to be rather large and usually somewhat predatory, the estuarine Bagrid Mystus gulio (over 40 cm/16") being a classic example. But there are a few smaller species among them, such as Mystus wolffii, a peaceful but predatory fish that does well kept in groups alongside other medium-sized tankmates. Growing to around 20 cm/8" in length it cannot be trusted with very small tankmates. The Kerala catfish Mystus armatus is a smaller (14 cm/5.5") but otherwise similar species. Like the barbs, these are species that tolerate rather than require salt, so a specific gravity below 1.005 is recommended. Besides catfish, there are also loaches in these brackish water streams. Of the species traded, the bizarre horseface loach Acantopsis choirorhynchos is one of the most appealing. It is a retiring animal that likes a tank with a soft substrate into which it can burrow, often completely hiding itself away from view. In a tank with a sandy substrate it performs a very useful service in turning over the sand and eating up any leftover food that it finds. It can't survive on leftovers alone though, and will appreciate all sorts of frozen foods, in particular insect larvae and Tubifex worms. There is a look-alike species known as the long-faced loach Acantopsis octoactinotos; although smaller (to 9 cm/3.5"), this Indonesian species is less welcomed by aquarists because it seems to be a good deal more territorial and predatory than the rather inoffensive horseface loach. Telling the two species apart isn't easy, but horseface loaches have snouts that curve downwards whereas those of the long-faced loach slope forwards. The horseface loach is also much more of a burrower, whereas the long-faced loach is content to hide among rocks and bogwood.

Spiny eels are among the most popular fishes from this part of the world, with many retailers stocking them and many hobbyists buying them. Although essentially hardy and adaptable, and even rather intelligent, spiny eels are often not a success in home aquaria. There are several reasons for this. Firstly, spiny eels are nocturnal predators, and simply won't eat flake food or catfish pellets; contrary to myth, they aren't scavengers. Spiny eels need to be provided with live foods immediately after import, particularly things like earthworms, clean Tubifex, and bloodworms. These should be offered at night, and it is important that they aren't kept with catfish or loaches, as those fish will usually steal the food before the spiny eels get a chance to feed. Once settled, spiny eels will happily feed during the day, and take all sorts of things including shelled prawns and small bits of white fish. Of the many species that live in India and Sri Lanka, the most commonly traded ones that naturally inhabit brackish waters are the tyre-track eels Mastacembelus armatus and Mastacembelus flavus, but these are both giant fish (up to 90 cm/3') and far too predatory for the type of aquarium being discussed here. Macrognathus aral, the one-striped spiny eel, is another brackish water species from South Asia, but it is also rather large, getting to around 60 cm/2' in length, and though not quite so piscivorous as the preceding species, it could well view any small tankmates as food. Perhaps the best choice is the barred spiny eel Macrognathus aculeatus, a relatively small (40 cm/16") species that feeds almost entirely on insect larvae and worms, and can be safely kept with all but the smallest tankmates. Although not found in South Asia, the widely traded peacock spiny eel Macrognathus siamensis could be used as a substitute. Besides being easier to obtain, it is only half the size of Macrognathus aculeatus and consequently much less predatory.

Gobies and flatfish are two of the most characteristic fishes of brackish waters around the world, and various kinds of both make it into the aquarium trade. Of the various bumblebee gobies traded (Brachygobius spp.) most are confined to Southeast Asia, but one species, Brachygobius nunus, is found in India and Sri Lanka. Actually identifying bumblebees to species level is essentially impossible with live fish swimming about an aquarium, so the aquarist will have to be satisfied with simply using whatever bumblebee gobies are available at the time. Bumblebees are found in a variety of fresh and brackish waters and tend to be very adaptable, but their are fussy about their food. Live foods, particularly daphnia and brine shrimp, are preferred, but once settled they will eat a variety of things including small chunks of prawn, bloodworms, and frozen lobster eggs. Take care that the gobies get a chance to eat, because they are rather slow. Another lovely little goby is the Rhinohorn goby Redigobius balteatus. In terms of care it is identical to the bumblebee, but it has a different set of colours: a silvery-white body marked with two black stripes, one vertical, the other oblique. A step larger in size is the very beautiful knight goby Stigmatogobius sadanundio. This goby gets to around 9 cm/3" in length and is a very accomplished predator, and will devour any small fishes it can catch, including smaller gobies! Though sometimes kept in freshwater, it is far healthier in a brackish water tank and puts on an excellent display, swimming about in the middle of the tank quite readily. Among the flatfish, the most regularly traded Asian species are in the genus Brachirus of which several occur in India. As with the bumblebee gobies, identifying these fish to species level is extremely difficult, so use whichever one you find; most should adapt well to a specific gravity around 1.005. Flatfish tend to be nocturnal, rather shy, and favour tanks with a sandy substrate into which they can burrow. They are predators, but with a preference for small worms and insect larvae. They will not do well forced to compete with catfish and loaches, but are otherwise fairly easy to keep.

The last word has to go the figure-8 pufferfish Tetraodon biocellatus. Pufferfish are, in general, poor community fish, if only because they view anything and everything in the tank as a potential meal. Keeping them with other fish usually works best where the tank is large, filled with hiding places, and all the other species are fast swimmers or else hide away in caves like gobies and catfish. On the scale of pufferfish nastiness, the figure-8 actually comes out pretty low, and it has been kept successfully with gobies, orange Chromides, and flatfish. This species is often sold as a freshwater fish, but it does better in a low salinity brackish water tank, and will thrive in the 1.003-1.005 range required by the other fishes described here.