Related FAQs: Brackish Aquariums In General, FAQs on Brackish Salty Water, Related Articles: Small Species for the Small Aquarium: A South Asian Coastal Stream by Neale Monks,Brackish Aquarium Keeping in General, Brackish System Components and Set-Up, Brackish Livestock Groups, Brackish System Maintenance, Brackish for Beginners, 2:  Big But Beautiful: A Southeast  Asian Estuary
© Neale Monks

Last month we considered a South Asian coastal stream where a mixture of salt-tolerant plants, freshwater fish, and marine fish come together to create an interesting basis for a community tank. The species looked at there were mostly small and inoffensive: something that cannot be said about the fishes being looked at this month. Estuarine fishes tend to be large and very active, so space and plenty of water current are important here. They are also adaptable omnivores, with some species being distinctly predatory, while others more than happy to eat aquarium plants given the chance. On the other hand, while these fishes may be demanding in some ways, they repay that effort by being attractive and often very unusual in shape and behaviour. Southeast Asia is home to many of the best brackish water aquarium fishes, so it is fitting that we model this tank after a Southeast Asian estuary.

 

Water chemistry

Brackish water with a specific gravity of 1.010-1.012 is required for this community, but it is also important to keep an eye on pH and hardness. All of these fishes want a pH around 8.0 and a high level of hardness. For this reason, many brackish water fishkeepers stick with using coral sand as the substrate and tufa rock for the decoration. This will certainly work well, but thereÃs no reason not to be a little more creative. Mixing coral sand with gravel can create some interesting effects, as can the addition of crushed coral and crushed oyster shells. Even pulverised mussel and clam shells can be used to enliven things a little. What matters more than the substrate is the presence of calcareous media in the filter, and that this media should be regularly cleaned or replaced to maintain its buffering potential. Incidentally, the relatively high salinity in this aquarium means that a protein skimmer will work quite well.

 

Plants and decor

Estuaries contain little in the way of submerged vegetation, but along the shores emergent plants such as mangroves, palms, and sedges are often abundant. So the thing to do is create an aquarium that suggests an under the waterline view of these emergent plants, using things like artificial tree roots, bogwood, and bamboo canes. There are also some excellent 3D aquarium backgrounds that model tree roots, and these would be an excellent addition to this aquarium. It is important to keep these decorations to the back and sides of the tank, because most of these fishes are open water swimmers that do not appreciate an aquarium that is filled with clutter. Instead, use the decorative objects to simply create areas of shade where fishes can rest and hide if they want. Scatter a few hollow, low-rise ornaments such as seashells and artificial logs across the bottom of the tank. These will be appreciated by species that like to stay hidden most of the time, such as moray eels.

The Southeast Asian fish fauna

The estuarine fishes of Southeast Asia are mostly members of otherwise marine fish families that are able to tolerate reduced levels of salinity. A notable exception is Mystus gulio, a member of the Bagridae, a predominantly freshwater family of catfish. It is more important as a food fish than an ornamental, being quite intensively farmed in South Asia especially because of its excellent flavour, its occurrence in the aquarium trade is sporadic at best. But its large size, peaceful (if predatory) nature, and its diurnal rather than nocturnal habits make it an excellent choice for the aquarist with enough space to house a small group of these schooling catfish. Mystus gulio is a variable species, with at least two distinct races. Mystus gulio from India are twice the size of those from Southeast Asia (40 cm/16" as opposed to 20 cm/8" in length) and tend to be brownish-grey in colour whereas the Southeast Asian specimens are more silvery-green. The Southeast Asian race seems to be the one usually seen in the trade. Although it will eat small fish given the chance but is otherwise content to eat catfish pellets, mussels, bloodworms, and other small meaty foods.

No discussion of Southeast Asian brackish water fish is complete without mentioning the scats and monos, the two best loved and most regularly seen examples of the lot. In terms of care, scats and monos are very similar: they like lots of swimming space, excellent water quality, plenty of oxygen, and a varied diet. But they are rather different in other ways. Scats are completely peaceful animals, and whether kept singly or in a school, these ñswimming stomachsî think about little else but scrounging their next meal from their weak-willed keeper. Monos on the other hand are fiercely hierarchical and sometimes bullying, and when kept in twos and threes will spend much of the time chasing one another. In some cases, the weaker fish will be badgered to death. Curiously, one thing that works well is to mix scats and monos together: their combined numbers seem to have a pacifying effect, diffusing some of the monos' belligerence. Three species of mono are traded, the common mono Monodactylus argenteus, the West African mono Monodactylus sebae, and the orange mono Monodactylus kottelati. Of these, only the common mono and the orange mono are native to Southeast Asia. The common mono is a rhomboid fish with dorsal and anal fins of equal length and with a yellow patch covering most of the dorsal fin. It reaches around 15 cm/6" in the home aquarium. The orange mono is very similar but has slightly more elongate anal fins while the dorsal fin is distinctly orange in colour. It is also smaller than the common mono, getting to about 10 cm/4" at most even in the wild. Unfortunately for the aquarist, these two species are never distinguished by importers or retailers. Monos are essentially carnivorous but readily take flakes and pellets. Periodic offerings of prawns and chopped fish and squid will also be appreciated.

Scats look a lot like marine butterflyfish in shape but there any resemblance ends! Where butterflyfish are notoriously picky about what they eat, scats will eat absolutely organic material they can stuff into their surprisingly delicate mouths. They are somewhat herbivorous in the wild, so the ideal diet for them in the aquarium should include plenty of greens, such as cooked peas and blanched lettuce. Vegetarian and Spirulina flake food make ideal staples. There are two genera of scat, Scatophagus and Selenotoca. The common scats are in Scatophagus and these generally get to about 20-30 cm/8-12" in the aquarium. The silver scat of the hobby is Selenotoca multifasciata supposedly reaches 40 cm/16" in the wild but aquarium specimens seem to level off at 20 cm/8" at most

After the scats and monos, the next most popular of the Southeast Asian brackish water fish are the archerfish, Toxotes spp. Contrary to popular belief, the majority of archerfish species are primarily or entirely freshwater in distribution, but it is true that the two most commonly traded species are brackish water fishes. These are Toxotes jaculatrix and Toxotes chatareus. Both of these are fairly large animals, and though they donÃt reach full size in the the home aquarium, they can still be expected to reach a good 15-20 cm/6-8" in length. They are also extremely predatory, despite being thought of as purely insect-eaters. Archerfish can and will eat anything they can capture with their very large mouths. A smaller species, Toxotes microlepis, is quite regularly traded as the freshwater archerfish but is also muddled up with Toxotes jaculatrix on a very regular basis. Though its smaller size (around 12 cm/5") makes it very appealing, it doesnÃt like strongly saline conditions and will not prosper in this aquarium. At around SG 1.005, on the other hand, it does very well.

Among the other perciform fishes in Asian estuaries is the target perch Terapon jarbua, a species that slips in and out of the trade never quite making the same impact as archers, scats, or monos. Part of the problem is its temperament. Juvenile fish are territorial and snappy among themselves and frequently nippy towards their tankmates. Adult fish, by contrast, are relatively peaceful if boisterous schooling fish. Aquarium specimens reach about 30 cm/12" in length, but only become good community fish once they have reach about a third that size. Anything smaller, and the aquarist should be prepared for trouble! The tigerfish of the genus Datnioides are a bit more regularly seen. There are several species in the genus, but only two are suitable for the high salinity brackish water aquarium, Datnioides polota (formerly Datnioides quadrifasciatus) and Datnioides campbelli. These are large (over 30 cm/12"), territorial, predatory fish that need lots of hiding places.

Although most gobies are rather small, there are some large species that can work well in communities of robust fishes, particularly among the sleeper gobies. Eleotris fusca is a typical sleeper goby, being fairly large (20 cm/8"), territorial, highly predatory, but otherwise peaceful. The crazy fish Butis butis is similar in habits but a bit smaller at around 15 cm/6" at most. Its common name refers to its ïcrazyà habit of resting at odd angles in the aquarium, perching on vertical surfaces, upside down in caves, or anywhere else that takes its fancy. Its mottled colouration resembles decaying vegetation, so presumably the crazy fish attempts to blend it with its surroundings by trying to look like a dead leaf or floating twig. In the process it hides itself away, ready to strike at any small fish that swims by. Although it prefers live food, like other sleepers it is easily trained to take prawns, whitebait, and other small items of seafood.

Though traded as a goby, the butterfly-goby waspfish Neovespicula depressifrons is not a goby at all. Resembling a small (10 cm/4"), brown grouper this fish is predatory but otherwise peaceful and highly entertaining species. It prefers live foods such as river shrimps and earthworms, but can be weaned onto dead foods without too much bother once settled in. As the ïwaspfishà part of its name might suggest, this fish is armed with venomous spines and should be handled with care. Superficially similar is the grunting toadfish Allenbatrachus grunniens. A much larger (30 cm/12") but equally predatory fish, this fish is most remarkable for its noisiness. At night especially, these fish will make surprisingly loud grunts, particularly when sexually mature! Both the waspfish and the toadfish are best weaned onto dead foods by the old ñdangle the food in front of its faceî trick, but this will take time and it may be days before your fish decides to accept a new food item. Once settled in though, both species are hardy and easy to keep. On no account underestimate the predatory instincts of either species: they can and will capture prey not much smaller than they are. Always keep with larger tankmates.

Pufferfish are always controversial as community fish because so many people have had bad luck mixing puffers with other species. Pufferfish certainly can be territorial, and some species are predatory as well, though none of the brackish water species. The most commonly traded brackish water puffers are known as green spotted puffers in the trade but as Tetraodon fluviatilis and Tetraodon nigroviridis to scientists. These two species are very similar in appearance, but Tetraodon fluviatilis tends to have large blotches on its back whereas Tetraodon nigroviridis is almost uniformly covered in small black spots. They are fortunately rather similar in needs and behaviour, being fairly large (around 15 cm/6") when mature and thrive in strongly brackish water. Like other puffers, they are intolerant of poor water conditions, especially high levels of nitrate, so are not suitable for heavily stocked or inadequately-filtered aquaria. Both species are generally tolerant of tankmates but odd specimens can become fin-nippers or aggressive. A much more reliable community species is Arothron hispidus, the dog-faced puffer. Unfortunately this species is rather large, at least 30 cm/12" when mature, and is normally sold as a relatively expensive marine fish. It adapts well to high-salinity brackish water systems though, particularly when young.

ñFreshwaterî moray eels, Gymnothorax tile, are in fact nothing of the sort, and all such species are really brackish water fish. They are not great community fishes, tending to be view tankmates as food once they reach a certain size. Kept on their own they make an interesting addition to the brackish water aquarium, but when mixing with other species choose large tankmates and keep an eye out for signs of trouble (like bite-marks!). Keeping the morays well fed probably helps, too. Regular helpings of prawns, squid, whitebait, and other meaty foods are important. They are often loathe to take such things at first, insisting on live foods. River shrimps work well for this, but once the moray has put on some weight, cut back the live food and wean them onto the alternatives. The neat little spaghetti eels, Moringua spp., are scaled-down (around 40 cm/16" long) cousins on the morays and much easier to mix with other fish. They feed entirely on small invertebrates, particularly worms, and do best kept in groups in a tank with plenty of open, sandy areas for burrowing. Sadly, they arenÃt that widely traded. Their smaller size (or thickness, at least) does make them a bit more vulnerable to predation, so choose tankmates with care.

Final thoughts

These two articles should have made it clear that the brackish water aquarium is neither difficult to set up nor limited in its range of options as far as tank residents go. This list left off quite a few Southeast Asian fishes that would enjoy these water conditions but for one reason or another donÃt make great community fish. The Asian dragon goby Pseudapocryptes elongatus needs shallow water where it can beach itself to take a gulp of air, and mudskippers of course want lots of land and only enough water to dip themselves in from time to time. The river halfbeak Zenarchopterus buffonis is a spectacular fish but nervous and easily alarmed, so best kept alone or with smaller, benthic species such as gobies. The bizarre threadfins, Polynemus spp., are difficult to keep alive at the best of times, and definitely need their own tank if you want any chance of success. There are also various flatfish in the trade, but they are tricky to feed and donÃt really do well in busy community tanks. Even leaving out these challenging species, one of the nice things about the brackish water branch of the hobby is that new species appear all the time, and the Interest Imports section of PFK regularly features cool new brackish water species that would work very well in this type of aquarium. So watch this space!