North American Gar
Family Lepisosteidae
Gar are large, predatory fishes that are hardy and easy to keep in aquaria, provided they are given enough space.
Whilst they are primarily freshwater fishes in most of their range, several species enter brackish water and one or two species may even be found in salt water from time to time. Atractosteus spatula is particularly common in brackish water where they feed heavily on blue crabs. All gar are opportunistic predators that will eat pretty much anything they can catch including arthropods of various types, fish, small turtles, aquatic mammals and even wildfowl. Because of their large size and heavy armour, once they reach adult size, most species are relatively immune to predation though alligators will sometimes eat them.
Four species routinely enter brackish water and can be considered possible additions to the brackish water aquarium. These are:
- Atractosteus spatula, fresh, brackish and salt water, maximum length ~300 cm
- Lepisosteus oculatus, fresh and brackish water to at least SG 1.005, maximum length ~100 cm (~60 cm in home aquaria)
- Lepisosteus osseus, fresh and brackish water to at least SG 1.005, maximum length ~200 cm (~100 cm in home aquaria)
- Lepisosteus platostomus, fresh and brackish water to at least SG 1.005, maximum length ~90 cm (~60 cm in home aquaria)
Lepisosteus oculatus and Lepisosteus platostomus stay relatively small in captivity and can be kept safely in tanks 700 litres (200 gallons) in size without problems. The main issue with these fish is the width of the tank from front to back; because gar are inflexible fish thanks to their armour plating, the tank needs to be broad enough that they can turn around easily. In other words, the tank should be at least as broad as the fish is long. The bigger species are not viable fish for the home aquarium, and are more normally seen in public aquaria.
Broadly, gar can be considered community fish when kept with fish too large to eat. Docile cichlids, catfish, Siamese tigerfish, and large sleeper gobies like Dormiator maculatus work very well. Gar also get along with their own kind, and in fact actually prefer to be kept in small groups. They will eat practically anything meaty, from floating carnivore pellets through to chunky strips of fish and squid. Small specimens particularly enjoy bloodworms and other insects. There is absolutely no reason to feed them live feeder fish.
Water chemistry is relatively unimportant, and the brackish water species at least will tolerate a specific gravity of at least 1.005. They are air breathers, and must have access to the surface of the tank. Although many species are tolerant of stagnant water in the wild, in aquaria they do best in well-filtered water.
Sea Catfish
Family Ariidae
Sea catfishes make excellent aquarium residents, being hardy, peaceful, and easy to feed. Although predatory, they are gregarious and best kept in groups of at least three specimens. They mix well with other large, peaceful fish including scats, monos and archerfish.
Sea catfishes are powerful, sleek fish that swim strongly and as they cruise into estuaries and across shallow seas searching for their favoured prey, small fish and crustaceans. To help them find food they use their whiskers and electrical sense just like other catfish, but they also produce sounds apparently used for echolocation. More obvious to the aquarist are the continual drumming noises they make. These are probably used for some sort of communication. Sea catfishes possess glands in the mouth capable of secreting anticoagulants, which they use when hunting to weaken their prey. They are also well defended, with sturdy spines in the pectoral and dorsal fins armed with a powerful venom. Needless to say these fish should be handled with care.
In South America sea catfish are sometimes called ‘crucifix fish’. When cleaned and suitably painted, the skulls of these fish are sold as curios. On the underside a crucifixion scene can be imagined, and on the dorsal surface a bishop raising his arms in a blessing. The name of one genus of sea catfish, Arius, signifies that the fish is ‘of the war-god Ares’, not altogether unfitting considering their impressive adaptations to the predatory lifestyle! All in all these are fascinating fishes.
The Colombian shark catfish Sciades seemanni is by far the most widely traded sea catfish. They do well in large tanks with ample swimming room and a strong water current. Salinity isn’t critical, but aim for around SG 1.005 for juveniles and SG 1.010 for adults. This species can also be kept in a marine aquarium. Maximum size in aquaria is around 15-20 cm (6-8 inches) though in the wild this species can be twice that size. This species is very gregarious and easily bullied, so choose tankmates with care. Older books refer to this species as Arius seemanni, Arius jordani, and Hexanematichthys seemanni.
Some species of the closely related genus Arius have been bred in captivity, but not the Colombian shark. This is presumably because of some missing trigger, but what that might be is not known. The small size of the Colombian shark should mean that captive breeding is possible. In captivity at least, this species reaches about 30 cm (12 inches) in length, but the females are noticeably stockier than the males and develop swollen pelvic fins when mature. Many ariid catfish mate in summertime at sea, the male brooding a few large eggs in his mouth until they hatch, when he deposits the young fish in rivers and offers them no further protection.
Occasionally other sea catfish appear in the trade, such as Hexanematichthys sagor (see photo below). Apart from differences in size and potentially water chemistry requirements (some species are strictly freshwater fish) basic care is consistent and similar to that required by Sciades seemanni.
Sleeper Gobies
Family Eleotridae
Although similar to the gobies, sleepers lack the fused pelvic fins (the ‘sucker’ on the belly). Sleeper gobies tend to be fairly large, omnivores with a taste for small fish, and rather territorial towards one another. But when combined with fish they can’t swallow, they are excellent community fish. Most species are extremely hardy and generally easy to keep.
The commonest sleeper goby traded, Dormitator maculatus, is sold as a pretty little fish that barely hints at the 25 cm plus (over 10 inches) monster it can potentially become. It is essentially a predatory fish, but will accept chopped up mollusc and crustacean meats as well as fresh white fish. It is found along the entire east coast of tropical South and Central America in brackish and marine water. Occasionally it enters freshwater, but it is much healthier in water that has some salt added. When small the colouration is rather plain, with an overall pale brass coloured body with dark bands on either flank. With age a colourful pattern of red and blue spots develop, which the fish seem to be able to change with their mood. Like many sleepers, the eye tends to have a glassy look, as if the fish is unconscious. Hence the name, perhaps?
A similar species from West Africa, Dormitator lebretonis, is offered for sale fairly regularly. It is sometimes called the African goby or clay goby. It is much smaller (around 10 cm when fully grown) and suitable for both freshwater as well as low salinity brackish water systems.
Another predatory sleeper is the crazy fish Butis butis. Growing to around 15 cm (6 inches) this fish is rather more territorial than the common sleeper. It is handsome if sombre, being various shades of mottled brown in colour looking rather like a bullrout. Basically nocturnal this fish will feed on any invertebrate or fish it can overpower. Found in fresh, brackish and salt water it will adapt to most conditions although some salt is recommended (specific gravity 1.005 to 1.015). This fish gets its common name for its habit of perching upside down beneath overhanging rocks or pieces of wood, and sometimes in midwater.
The Australian/New Guinean sleeper goby Bostrychus zonatus is an uncommonly traded species noted for its relatively small size (around 13 cm) and handsome rather than colourful appearance (see photo below). Like all sleepers it is predatory and territorial, but is otherwise peaceful and makes a good community fish when combined with species of similar size. Though sometimes traded as a freshwater fish, a low salinity around SG 1.005 is recommended.
Siamese and other Tigerfish
Family Datnioididae, Coius or Datnioides spp.
Tigerfish are a small family of peripheral freshwater fish restricted to Southeast Asia from India to New Guinea. They resemble snappers in basic shape, with a laterally compressed body, large eyes, and a very big mouth. The soft parts of the dorsal and anal fins project backwards and are positioned close to tail fin, resulting in a distinctive configuration that has given them the common name ‘tripletail’ among ichthyologists, the name ‘tigerfish’ being more widely used among aquarists and fishermen.
In terms of ecology tigerfish are all solitary stealth hunters. They prefer to hide among plants waiting for prey to swim into range. The light and dark stripes on the flanks and the pale stripe down the forehead all serve to break up the outline of the fish, making it more difficult for its prey to spot.
Tigerfish have a preference for large, well-planted tanks with lots of hiding places. In freshwater or slightly brackish conditions, plants such as giant Vallisneria and robust Sagittaria can be used to provide precisely the environment they like. Alternatively plastic plants can be used, and this may be preferred in tanks where the salinity is too high for freshwater plants to do well.
Tigerfish are territorial but otherwise peaceful predatory fish that mix well with other types of fish that are too large to be eaten. Scats, monos, ariid catfish and archerfish all make excellent companions, provided such tankmates are at least equal in size to the tigerfish. Some species will tolerate other tigerfish (either their own kind or other species) but others are much more aggressive.
All the tigerfish are predatory and prefer live foods. In the wild they are reported to feed on crabs, prawns, fish and insect larvae. In the aquarium they are very adaptable and happily take river shrimps and earthworms; once settled they will also accept frozen fish, chopped seafood, and sometimes even pellets. They quickly become tame, and can make extremely good pets.
Five species are currently recognised, of which three are primarily freshwater fish in the wild, while two are found in both fresh and brackish waters. In captivity all species have been found to be extremely adaptable, and the freshwater species do perfectly well in low salinity environments. Conversely, the brackish water species appear to be able to live long and happy lives in hard, basic freshwater aquaria.
Freshwater species (freshwater to SG 1.005)
- Datnioides microlepis
- Datnioides pulcher
- Datnioides undecimradiatus
Fresh and brackish water species (freshwater to SG 1.010)
- Datnioides campbelli
- Datnioides polota (= D. quadrifasciatus)
Commonly Traded Species
- Common or Four-stripe Siamese Tigerfish, Datnioides polota
- One of the most frequently seen species is the Siamese tiger fish Datnoides polota (= D. quadrifasciatus), a species naturally found in estuaries and able to do equally well in either hard freshwater or brackish water conditions (up to SG 1.010). It is a very attractive species when young, being silvery white and bearing one thick black stripe running vertically through the eye, four more on the flanks, and then at least a couple more along the tail between the dorsal fin and the caudal fin. As the fish matures the contrast between the stripes and the background colour lessens while the fish takes on a more brassy or brownish hue. It generally tolerates conspecifics well and makes a good community tank fish.
- Finescale or Three-stripe Siamese Tigerfish, Datnioides microlepis
- A second species of tiger fish widely offered for sale is the finescale or three-stripe tiger fish Datnoides microlepis. It is outwardly very similar to the Siamese tiger fish, though as the common name suggests some specimens have three stripes on the flanks instead of four. Although tolerant of slightly brackish water SG 1.005 or less, it is a strictly freshwater fish in the wild. Social behaviour is similar to D. polota.
- New Guinea Tigerfish, Datnioides campbelli
- Datnoides campbelli is a truly euryhaline species that in the wild migrates freely between fresh and brackish water in search of food. It is best kept at a specific gravity of 1.005 to 1.010 depending on the needs of its tankmates. Compared with the other Datnoides it has a warmer, more mottled background colour against which the stripes are set, and the head region is more or less completely dark. Datnoides campbelli has a mixed reputation as far as sociability goes, with some aquarists considering it to be rather aggressive compared with the other tiger fish.
Ropefish or Reedfish
Family PolypteridaeFreshwater Morays
Family Muraenidae
Although traded as freshwater fishes, these fishes really need moderately brackish water to do well, and most probably prefer salinities approach normal seawater. As such, they can mix well with scats, monos, and other large, high-salinity brackish water fish. However their social behaviour can be unpredictable. Some aquarists have kept groups without any problems, while others have found them to be much more territorial and aggressive. Similarly some specimens ignore large fish too big to swallow whole, while others repeatedly attack their tankmates.
Thomas Flörkemeier reports that Gymnothorax tile is killled by copper-based medications. Aquarists keeping freshwater morays should consider this when using many of the commercial medications and act accordingly.
Hunger Strikes & Feeding
Moray eels almost invariably stop feeding when kept too long in water with insufficient salinity. But provided the fish is being maintained at a middling salinity (around SG 1.010) these fish tend to be reliable, even aggressive, feeders. There is no need to offer them live feeder fish; river shrimps can be used to help settle in a new specimen, and after that it should take any sort of chunky seafood. Mixed frozen seafood (typically squid, prawn and mussel) sold for human consumption will make an ideal staple diet.
Bear in mind that morays are largely nocturnal, so the evening is likely to be the best time to feed them. Morays are said to become confused when too much food is put in the tank at once, perhaps because the source of the scent is difficult to locate, so offer only small amounts at a time.
Moray eels have sharp teeth and mildly toxic saliva; while not aggressive, they should be treated with respect.
Common Freshwater Moray
Gymnothorax tile is by far the most commonly sold ‘freshwater moray’ in the hobby. It is pinkish-grey in colour and covered in many tiny cream spots. The biology of this species is not fully understood but it is believed to be anadromous, meaning that it inhabits brackish and marine waters as an adult but breeds in brackish or fresh water. It is a large fish, potentially reaching 60 cm (24 inches) in length.
Other Freshwater Morays
A related species, Gymnothorax polyuranodon, is sometimes sold and is distinguished by a giraffe-like pattern of dark brown patches on a cream coloured body. It is believed to be a catadromous species, that is, while adults may inhabit brackish or fresh waters for extended periods, they return to the sea to breed. Aquarists have found that this species does best in at least moderately brackish water (SG above 1.010); if the salinity is too low this fish will stop eating and becomes lethargic. It is by far the biggest of the ‘freshwater morays’, the largest specimens exceeding lengths of 90 cm (about 3 feet).
Echidna rhodochilus is gets to about 30 cm (12 inches) in length and is basically a light brown in colour, darkening on the back; the most characteristic feature are light patches on the sides of the mouth. Like all moray eels, these fish are predators, but they are especially fond of small crustaceans such as shrimps (river shrimp are ideal). Species of Echidna have flattened, shell-crushing teeth rather different to the needle-like teeth of most other morays.
Freshwater Bullrout
Family Tetrarogidae
The freshwater bullrout generally seen in tropical fish shops is Notesthes robusta and is imported from Australia. It has little to recommend it as an aquarium fish. Besides being inactive during the day and highly predatory, it has venomous spines in the dorsal fin which can deliver a painful sting. Bullrouts are variable in colour and pattern, but most are usually mottled in shades of tan and brown. They grow to about 30 cm (12 inches) in length. Bullrouts are found in fresh, brackish and marine waters around Australia and so will adapt to most water conditions. A specific gravity of about 1.010 is adequate for long term health, and will allow it to be combined with big fishes like shark catfish well able to look after themselves.
Although it prefers live foods (worms, fish and shrimp) it can be weaned onto chunks of meat and frozen foods. One way to coax a bullrout to feed is to dangle chunks of food in the tank close to its face. Tie the food using lengths of cotton -- keep your hands well away from this fish! Wriggle the food about, and with any luck, it will assume the food is alive and make its attack. After a while it should get the idea and be much easier to feed.
A soft substrate of fine gravel or sand will allow the fish to settle down comfortably, and show its ability to hide to best effect. Swimming space is not so important and the tank does not need to be particularly deep. A good filter is essential, as with any big predatory fish, as is subdued lighting.
Flatfish, Flounders & Soles
Freshwater Order Pleuronectiformes
Freshwater soles and flounders are commonly offered to aquarists as novelty fish, but unfortunately they are
relatively difficult fish to look after well. All are shy, nocturnal, and exhibit a distinct preference for live foods. None can compete with more active or aggressive fish, such as catfish or cichlids. Consequently many, if not most, of the freshwater soles sold to aquarists end up starving to death. The name ‘freshwater sole’ is also somewhat misleading, given that many have a distinct preference for brackish conditions over plain fresh water.
Because it is so difficult to identify these fish to species level, deciding on the optimal salinity for these fish is tricky. While a few species, such as Brachirus harmandi, Synaptura salinarum, and Cynoglossus waandersii, complete their entire life cycle in freshwater, most of the species traded as freshwater soles in fact move freely between fresh and brackish (and even fully marine) waters. Adult hogchoker soles, for example, can be found far out to sea as well as hundreds of miles up rivers. Nonetheless, many aquarists have found that they do best in brackish rather than fresh water. Therefore unless you can positively identify your ‘freshwater sole’ as a truly freshwater species, it is probably safest to keep it in slightly brackish water (with a specific gravity of around 1.005). The truly freshwater species can easily tolerate a specific gravity this low, so even if you happen to misidentify a freshwater species as a brackish water one, no harm will be done.
Freshwater soles also seem to be intolerant of low oxygen levels and will swim to the surface and ‘gasp’ if the water is not adequately aerated.
All freshwater flatfish require a aquarium with plenty of open sand or fine gravel into which they can burrow. Because these fish can alter their coloration so that they can blend in with the substrate, brightly coloured substrates (such as blue or red artificial gravels) must be avoided. River sand, smooth silver sand, and pea gravel are good choices, but remember that sandy substrates cannot be used with undergravel filtration systems. Ornaments, rocks, and plants can be used in tanks containing freshwater soles, but these should be kept to the edges or back of the tank so that plenty of open sand or gravel remains.
These fish are essentially hardy and do not seem to be as prone to diseases like whitespot as many other aquarium fish. Neither do they seem bothered by high levels of nitrite or ammonium, at least over the short term. I have used Brachirus sp. to run in a brand new aquarium without any obvious problems. However, these fish are difficult to feed because they are so nocturnal, and even when they do swim about in the day, they do not seem to feed. Frozen bloodworms and mysis shrimps, small pieces of prawn and squid, and live foods such as earthworms and river shrimps, are all taken by these fish, but it is essential to offer these at night once the lights are out and the other fish in the tank cannot feed.
The most commonly traded species are:
Family Achiridae (American soles)
- Achirus lineatus, the South American lined sole (prefers brackishor marine water)
- Trinectes maculatus, the hogchoker sole (prefers brackish or marine water)
Family Cynoglossidae (tongue soles)
- Cynoglossus spp., Asian tongue soles (includes some strictly freshwater species)
Family Soleidae (true soles)
- Brachirus orientalis, the oriental sole (prefers brackish or marine water)
- Brachirus harmandi, the freshwater sole (a freshwater species)
- Brachirus pan, the true pan sole (prefers brackish water)
- Brachirus panoides, the false pan sole (either fresh or slightly brackish water)
- Synaptura salinarum, the salt pan sole (a freshwater species)
Telling these families apart is generally not difficult: the Achiridae usually have rhomboid bodies with small heads but large, paddle-like tails. The Cynoglossidae are very elongate and leaf-like, with small, tapering tail fins but a large, shovel-shaped head. Finally, the Soleidae have a leaf-like shape similar to the Cynoglossidae though not always so elongate, and the head is small and rounded. The FAO fisheries guide to Sri Lanka includes some helpful diagrams for distinguishing typical examples of the Cynoglossidae from the Soleidae.
Besides the species listed above, other species may be imported from time to time, but identifying any of them is tricky because there are several lookalike species and all are able to change their colouration and markings to some degree.
Spiny Eels
Family Mastacembelidae
Spiny eels are found in Asia and Africa, usually in freshwater habitats but sometimes in slightly brackish water. As such, a few species can be considered for inclusion in low salinity brackish water systems (SG 1.005 or less).
Species that occur in brackish water include:
- Macrognathus aculeatus, to 38 cm
- Macrognathus aral, to 60 cm
- Macrognathus pancalus, to 18 cm
- Mastacembelus armatus, to 75 cm
Spiny eels are not easy to keep. They are easily damaged by abrasive gravel, and then secondary infections, likely Aeromonas and Pseudomonas spp., quickly set in. Another major problem is feeding them. They will not accept dried or flake foods, and tend to be slow at feeding time even when the right foods are offered. Worms, especially earthworms, as well as insect larvae and small crustaceans are the favoured food items. By choice they feed at night, but once settled into the aquarium they become more willing to feed by day. Spiny eels are best not mixed with other nocturnal species such as catfish; that way, any food put out at night will be eaten by the spiny eels alone.
Social behaviour varies. The spiny eels in the genus Macrognathus tend to be gregarious and are best kept in groups; by contrast species of Mastacembelus are territorial and can be very aggressive towards one another. All species are predatory towards fish that are small enough to swallow whole. Large species like Mastacembelus armatus can easily manage taking fish as large as swordtails and mollies.
Needlefish
Family Belonidae
Xenentodon cancila or Asian needlefish are quite large predatory fish closely related to the halfbeaks and similar to them in basic shape. Maximum size in aquaria is around 30 cm (12 inches). They are sociable and need to be kept in groups, and consequently the aquarist will need to set aside a large aquarium for this species. Needlefish are very nervous. It is recommended that the tank be planted around the edges and back to allow the fish to recognise the boundaries of the aquarium and so avoid damaging itself when alarmed. These fish often jump, and can easily damage their jaws by flying into the hood or the sides of the tank. Floating plants and gradual rather than sudden changes in lighting will help. Needlefish prefer live foods including river shrimp, woodlice, earthworms, and insects such as mealworms and small crickets. They may also be weaned onto dead foods such as whitebait and silversides. Wild fish feed almost entirely on aquatic crustaceans; the idea that they feed on small fish is erroneous (though they certainly will eat small fish in the aquarium, given the chance).
Wild specimens are found primarily in freshwater and only rarely in brackish waters or the sea. Even so, a small amount of salt (around SG 1.001-1.002) is often said to improve its general health, and in captivity it can be expected to do well in low-salinity brackish water aquaria (to SG 1.005). Not an easy fish and best ignored by beginners, though experienced aquarists will doubtless find this species attractuve and rewarding.
Occasionally some other species are traded, such as various species of South American needlefish, Potamorrhaphis spp.; these have proved extremely delicate and difficult to keep alive. Most of these species need soft and acidic water but a few are brackish as well as freshwater animals. Either way, perfect water quality is required, and even then they do not seem to do well in captivity. Best avoided.
Neovespicula depressifrons
Butterfly-goby Waspfish
Warning! This fish is venomous, and can deliver a very nasty sting through the spines in its dorsal and pectoral fins. Avoid handling this fish, and never touch it with your hands. While the sting is not known to be fatal, as with any venomous fish, if you are stung, you should seek medical attention at once. Children and people who react badly to animal stings (such as bee stings) probably should not keep this fish.
Neovespicula depressifrons is a small, grouper-like predator that can easily be mistaken for a bullrout at first glance. Like the bullrout, it is predatory, but given that it only grows to around 10 cm in length, can be easily raised on small invertebrates such as earthworms, Gammarus, and river shrimp. Small fish are also taken, but besides the ethics of feeding living fish to another fish, this approach is expensive and can introduce all sorts of parasites and diseases (especially when cheap feeder guppies are used).
Neovespicula depressifrons is sold under a variety of names, including “butterfly goby”, a name also used for the true goby Awaous flavus. It is not a goby at all, but a waspfish, a member of a small family of chiefly marine fish that are well known for being venomous. In terms of maintenance it is not demanding. In the wild it inhabits a variety of waters from completely freshwater through to fully marine conditions, but in captivity it can be expected to do well in brackish water with a specific gravity from 1.010 upwards. Unlike the bullrout, it is a day-active fish, and usually swims about at the front of the tank looking for food. Anyone seeing a tankful of these fish will be instantly struck by their cute behaviour and surprisingly attractive colouration, which varies depending on the decorations in the tank. The body is a mottled brown, but there is a light stripe running from the nose along the ridge of the back. The pectoral fins are huge, and used like paddles. The dorsal fin is tallest at the front, and when raised makes the fish look like it has a ‘mohican’ hair-do.
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