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Brackishwater Frequently Asked Questions

(3) Commonly Available Fishes

(3a) Monos (Monodactylus spp.)

There are two species of mono available. Both species are hardy, active fish well suited to a large brackishwater community. As juveniles they naturally occur in fresh and brackishwater, but the adults are essentially marine but make forays into estuaries and mangroves to feed. Spawning is believed to occur in freshwater, but only the true fingerfish Monodactylus sebae has spawned in captivity. Monos need plenty of heat, from 25 to 30 degrees-C (77 to 86 F).

The commonest is the widely distributed Malayan angel Monodactylus argenteus. This fish is found from South Africa east to Australia. It has a silver, circular body with triangular dorsal and anal fins splashed with black and yellow. The Malayan angel rarely reaches more than 15 cms (6 inches) in length in captivity, but can get significantly larger.

Restricted to Africa is the fingerfish Monodactylus sebae which is much more deep (and angelfish like). It lacks the yellow of the Malayan angel, but the dark grey or black bands running from the dorsal to the anal fin are much bolder. This fish is much deeper than it is long, and needs plenty of depth. Don't keep adult fingerfish in aquaria less than 60 cms (24 inches) deep. This species has occasionally spawned in large aquaria. Adults of this species can be kept at a lower salinity than of M. argenteus but should not be kept in freshwater for long periods.

Monos panic easily, turning from silver to grey or black, and breathe heavily. Such fish should be left to recover quietly. It is best to keep monos in the biggest tank you can get; adults resent being moved and may die if you try. A tank of at least 160 cms (4 feet) will be needed for a shoal of adults (at least 4 to 6 individuals of one species).

The young fishes are adaptable to freshwater, but with age they need to be kept in more and more salty water to do well. Eventually adults (over 10 cms in length) need water of salinity close to seawater (specific density 1.010 upwards). Adults are much more shoaling fishes, and restlessly swim up and down the tank. This can be disconcerting to some, more placid, fishes. Both species benefit from hard, well buffered water and the use of a protein skimmer and UV sterilisation helps to keep the adults healthy. Fluctuations in salinity are also useful, but care should be taken during water changes not to stress the fish.

Both species are predatory, but pose little threat to other fishes so long as they are not too small. Crustacean and mollusc meat are ideal staples, but most specimens adapt well to flake or pellets. Some greens may be taken, but as a rule they don't harm plants. Like scats they feed greedily, but take care not to overfeed.

(3b) Scats and Argusfishes (Scatophagus and Selenotoca spp.)

There are a number of closely related species traded as argusfishes or 'scats'. All are large, active omnivores with a distinct taste for plant material. The insatiable appetite of these fishes is legendary among aquarists. They quickly learn to take novel food items, including flies shot down by archerfishes (see below). Scats need the same sort of warmth as monos and archers, from 25 to 30 degrees-C (77 to 86 F). These are good community fishes, and like Monodactylus they are constantly active. Adults need plenty of space: an aquarium of around 120 cms (4 feet) in length and as wide and deep as possible.

The genus Scatophagus includes the most widely available fish, and are found all over the Indo-Pacific. Selenotoca is more localised, restricted to New Guinea and Australia.

Scatophagus argus is available in a range of colour varieties which may or may not be true subspecies. The commonest variety reaches over 30 cms in length. As a juvenile it is quite rounded in shape with variable colours but basically a spotted brown to green. One variety, the ruby scat (Scatophagus argus atromaculatus or "Scatophagus rubifrons "), has flecks of red over the body, especially along the back. Both become bronze to silvery brown when mature, with dark spots and a distinctive, hump-backed appearance. The African scat Scatophagus tetracanthus has stripes running vertically on the body when small, but is otherwise similar as an adult.

The Australian or silver scats Selenotoca spp. are more attractive aquarium fishes. They never grow so large, reaching about 20 cms. The juveniles and adults are similar in appearance, being a rich silvery white in colour with bold black stripes and spots. The dorsal fin is flecked with red and gold. These fishes usually command a higher price than Scatophagus but a shoal of these lovely fishes is equal in beauty to any reef fish. They are hardy and no more difficult to keep than common scats.

Both are easy to keep. They do best in shoals, and mix especially well with monos and archers which share similar needs and have the same quiet nature. Scats do not do well with aggressive fish. They appreciate a diverse diet with lots of greenery, like lettuce or pondweed, as well as animal protein. They take to flake well.

At least some species of Selenotoca and maybe Scatophagus have venom glands in the dorsal fin. It is always best to be careful when handling these fish. Although not dangerous to most people, be aware that those allergic to stings in general may react badly.

All scats seem prone to 'pop eye', an infection of the tissues of the eye which causes it to swell. Although not fatal, it is unattractive and difficult to treat and subsides only slowly. Rough handling, coarse netting when moving the fish, and scratches from the aquarium decor are possible causes. Changing the salinity of the tank on a regular basis, as with Monodactylus, is a good way to maintain general health.

(3c) Archerfishes (Toxotes spp.)

There are two commonly seen archerfishes, but they differ hardly at all in maintenance. Toxotes jaculatrix is known as the common archer. This is a deep bodied fish, bright silver in colour with bold black bands along the side and dark edges to the anal and dorsal fins. Toxotes chartreus is similar but has smaller spots between the black bands along the body. Both species grow to about 25 to 30 cms (up to 11 inches), so a large tank (over 100 cms, 3 feet) is needed.

In the wild these are schooling fishes. Opinion is divided as to the behaviour of these fishes in captivity, but as a rule it is best to keep either a single specimen or a school of similar sized individuals. They can be aggressive to one another but are totally benign toward their tankmates.

Archers specialise in catching aerial insects. They sometimes leap (like salmon), but are best known for spitting at insects, with a range of up to 150 cms. In captivity they can be 'trained' to do this quite easily. Begin by setting the tank up so that about 10 to 15 cms (4 to 6 inches) of glass is above the waterline. Once the fishes have settled in, feed them on small crushed prawn chunks. They will happily take these midwater. Then stick them to the glass at the waterline. The archers will pick them off. Gradually place the food a little higher each time. Eventually the fish will jump against the glass to get the food. Once the food reaches a certain height they give up jumping and start spitting. Enjoy!

Archers will adapt to almost all water conditions from medium hard freshwater to full strength seawater. They do well in planted tanks, especially 'paludarium' style set-ups. A specific gravity of 1.005 is fine for long term health. All archers appreciate warmth, from 25 to 30 degrees-C (77 to 86 F). They dislike 'new' water and do best in a mature tank.

(3d) Targetfish (Terapon jarbua )

The targetfish Terapon jarbua is typical of the family Teraponidae. It is a medium sized schooling predator of shallow waters both fresh and salt. They mix well with scats and monos with which they share similar needs. They are very active, and need plenty of space. In captivity the grow from 10 to 15 cms (4 to 6 inches) in size but can be larger. In the wild these fishes feed predominantly small fish and crustaceans, but are adaptable and in captivity will take pellets and frozen foods.

Targetfishes are periodically available but not so commonly as monos, scats or archers. Called targetfishes because when viewed from above, the dark bands over the silvery body give the appearance of concentric circles like an archery target.

(3e) Freshwater and brackish puffers (family Tetraodontidae)

Note: More pufferfish information can be found at the Puffer Page and Ian West's pufferfish site.

Freshwater puffers
These species do best in neutral, medium hard water, but the South American puffers and the red-eyed puffer will also thrive in soft, acid water. These species are freshwater only puffers:

Freshwater and weakly brackishwater puffers
There are some freshwater puffers that can tolerate - but do not require - salt. Keep at a specific gravity of 1.005 or below. These include:

brackishwater puffers
brackishwater puffers can are tolerant of a wide range of salinities, but appreciate hard water and a high (alkaline) pH. These puffers can be kept for short periods when young in freshwater without problems, although they may be prone to fungus and whitespot. A specific gravity of 1.005 to 1.015 is ideal for these species once mature. brackishwater puffers include:

Marine and strongly brackishwater puffers
Most marine puffers should be kept in full strength seawater, but there are some exceptions. They can be adapted to strongly salted aquaria with ease (specific gravity over 1.010). These fishes are discussed in more depth in the Marine Fish part of this FAQ (Part 7). They include:


Puffer fish behaviour
With a few exceptions, puffers are solitary fish, aggressive to to other puffers of any species including their own. Juvenile puffers can be more tolerant, but adults are almost always territorial and waspish in nature. They may tolerate non-puffer tankmates, but often do not. A few puffers are "fin nippers", especially the smaller species.

Fin nipping is most noticeable when puffers fight among themselves, but they will also go for slow moving fishes like catfish, cichlids and guppies. It is usually best to keep such puffers singly in their own aquarium. Being inactive the tank need not be large if just a single specimen is kept, so decor can be minimal. Aggression from puffers is usually betrayed by circular scars on the sides of their victims, as well as clean round bites taken from the fins.

These species become very large (up to 75 cms in the case of the Giant African puffer) and predatory and should be kept alone.


These species are not so big (up to 15 cms), but can still be waspish in temperament and are best kept without others of their own kind and only with other equally sized or bigger hardy fishes. In a big tank it may be possible to keep more than one specimen.


These species are peaceful toward other fishes but are aggressive towards other puffers of their own kind and perhaps to other species as well.


Few species are sociable among themselves. Provided the tank is big enough, more than one of these species can be kept. They are peaceful toward non-puffer fish as well. Both of these species can grow to over 15 cms.


Puffer fish care
Puffers need lots of shellfish in their diet, although some will adapt to pellet food. Shells allow the puffer to wear its teeth down, as rodents have to, because the teeth grow continuously. If the get too long the puffer cannot feed properly. In such situations, the teeth can be filed down with a needle file as sold for model makers.

For all puffers water quality is important. Like many marine fishes that have entered freshwater, they lack the ability to use air if the water goes bad, so a good canister filter and plenty of water movement will help to make them feel comfortable. Resist the temptation to overfeed, which will pollute the water quickly. Puffer fish will give the impression of being continuously hungry. In the wild their food is "high fibre", so they tend to gorge when feeding and then slowly digest their meal. If the food you offer is rich, reduce the portions appropriately.

Although puffers can be made to puff up, never do this out out of water. If they swallow air they may not be able to expel it afterwards. Stuck like this the fish cannot swim or breathe and eventually dies.

(3f) Chromides (Etroplus spp.)

Two species are seen in the trade, Etroplus maculatus and Etroplus suratensis . These are examples of the handful of naturally (many more have been introduced by man) occurring cichlids from Asia. They are considered to be quite primitive and may resemble the cichlids marine ancestors. Both are restricted to the estuaries and coastal rivers of India and Sri Lanka.

The orange chromide Etroplus maculatus is a small, peaceful fish well suited to aquarium life. The sexes are quite difficult to tell apart, although males of the natural colour morph tend to develop black patches on the flanks and dark edges to the dorsal and anal fins when in breeding condition. The artificial varieties, usually shades of orange or yellow, may lack these features. Orange chromides can reach about 8 cms (3 inches), and are quite easy to keep in brackishwater (specific gravity 1.002 to 1.010). This species is easy to spawn, although the parents do need live food as well as flake to 'condition' well beforehand.

Much larger is the silver or green chromide Etroplus suratensis (in captivity about 15 cms, 6 inches) which is a schooling herbivore. Keep in groups of six or more and feed with lettuce, cucumber and other vegetable foods as well as flake or pellets. Needs well salted water (specific gravity 1.005 to 1.010), unhealthy in freshwater. Rarely found in marine conditions but will tolerate full strength sea water, but even so should not be kept in a marine tank.

(3g) Kribensis (Pelviachromis spp.)

These small cichlids are characteristic of the slightly-brackish deltas and low lying streams of West Africa. They occur in fresh as well as slightly brackishwater, and adapt well to most water conditions provided extremes of pH and hardness are avoided. They are usually easy to breed, with large, robust fry that feed well on aquarium detritus as well as newly hatched brine shrimps. This makes them among the easiest of all egg laying fishes to spawn. As a rule they are territorial but not too aggressive, and both sexes have bright colours.

The common krib, Pelviachromis pulcher is a territorial fish and typical of the genus in most respects. The males are somewhat longer and thinner than the females. Females are quite rotund, and are marked with a plum coloured patch around the belly. Males may also have a series of "eye spots" on the upper part of the tail fin, but not always. They settle down quickly in a community tank, if provided with a lair of some sort (half a coconut shell, or a flower pot, make fine substitutes for the rocky overhangs they use in the wild). There is usually little problem in identifying matched pairs, as they couple will actively burrow in front of the lair. If you have other kribs in with them, especially males, it is best to remove them.

Once nesting, they will defend the lair vigorously; and like most cichlids are able to drive away even much larger fishes with surprising alacrity! Mated pairs will soon spawn, laying about 100 eggs. The female tends to the spawn, and the fry when they hatch after a few days. The male protects the female indirectly, through keeping the territory safe. Once mobile, the fry will graze contentedly on the detritus and algae within any mature aquarium. Anxious fishkeepers may remove the fry and rear them on newly hatched brine shrimps and finely broken up flakes. But usually the first thing the aquarist knows of his or her new generation of fishes is when the proud parents take the fry for feeding excursions around the tank!

All in all the krib is a delightful fish. But it does have some drawbacks. Firstly, it is territorial. In a small tank the other fish may not be able to retreat and can be hurt. Secondly, broods of fry often have a gross preponderance of one sex. If left in the tank, only the fastest growing, biggest fry will survive (usually males). Even if raised artificially, an excess of one sex may remain. The reasons for this are not clear, but pH and water temperature may be involved. A neutral pH may be the ideal; very alkaline systems tend to have more males, and very acid ones more females. Trial and error with successive broods may be one solution. The temperature of breeding tanks is often elevated to encourage spawning, with cichlids this may not be required, and in the case of kribs lead to sex ratio problems. About 22 to 25 degrees-C is fine for maintenance and breeding. Batches of just one sex are not desirable to pet stores, who prefer to sell pairs of cichlids.

(3h) Mollies (Mollienesia and Poecilia )

Mollies are the largest commonly sold livebearers, growing to an adult size of around 8 to 15 cms (4 to 6 inches). They are sometimes put in the same genus as guppies, Poecilia , while other authorities consider them to be quite distinct, warranting the seperate genus Mollienesia, from which the name 'molly' is derived.

All mollies are hardy and do well in fresh or brackishwater, but do demand a high degree of hardness and an alkaline pH. Mollies appreciate warmth, 25 to 29 degrees-C being about right; ensure aeration of the water is adequate since warm water holds less oxygen. They also need good filtration and a strong current. Some species can be adapted to marine conditions without problems, and are widely used to mature reef tanks. They are omnivorous, but do need greens in their diet. Spinach, cucumber and algae are readily taken. They also need space if they are to look their best. Mollies are very peaceful despite their large size, and should never be kept with aggressive fishes. Males may spar with each other but in a large tank rarely do any harm.

There are two sailfin mollies traded. The commonest is Poecilia latipinna which is available in a variety of colour morphs. The natural form is greeny silver. Males possess the large sailfin, as well a specially modified anal fin. The females are slightly larger. The giant sailfin Poecilia velifera is substantially larger but good specimens are not common. In the wild, both these species are found in a wide range of waters - from hard, fresh water to the open sea - and to some extent certain populations may have distinct requirements.

Smaller than the sailfin mollies are the shortfin mollies Poecilia sphenops and Poecilia mexicana . They are very variable fish, growing to around 8 cms (3 inches). Generally silvery green to blue, dark morphs of these fish have given rise to the black molly. In the wild these fish are fishes of running waters rather than the coastal lagoons favoured by the sailfins.

While mollies spawn easily, actually raising good quality stock is difficult. They need excellent water quality and a high pH and hardness to grow fast. The fry need plenty of space, especially the males, if the full sailfin is to develop. Crowding is one reason why captive bred mollies rarely grow as large as wild ones. Despite being among the commonest livebearers, mollies should not be overlooked and thought of as beginner's fishes.

(3i) Rainbowfishes (family Melanotaenidae)

Rainbowfishes are small fishes well suited to aquaria. They are schooling fishes from Australia and New Guinea, related to the silversides (Atherinidae) within which they are sometimes included. Although their ancestors came from the sea, they fill the tetra and minnow niches in the freshwaters of Australia and the neighbouring islands. Many are colourful, and most are quiet and very easily cared for.

The most commonly seen species belong to the Australian genus Melanotaenia, most of which are 8 to 15 cms (3 to 6 inches) in length when mature. Adult fish, especially males, are colourful and often develop high backs making the fish look quite impressive. They feed freely on flakes and small pellets, but augmenting the diet with mosquito larvae, small crustaceans, and similar foods on a regular basis will promote good colour.

Only a little salt is needed for most rainbowfishes. Like kribensis (with which they can be mixed) they are fish of rivers rather than estuaries. A specific gravity of 1.002 to 1.005 is adequate. They are gentle fish and can be combined with plants and other fishes easily.

(3j) Silversides or atherines (family Atherinidae)

Atherines are small or medium sized schooling fishes, so in aquaria it is best to keep at least six and preferably more. Most are marine, but there are some fresh and brackishwater species, some of which appear in tropical fish shops. The smaller species spawn quite readily if kept well.

Bedotia geayi is a medium sized, schooling fish well suited to mixed community tanks. Growing to 15 cms (6 inches) they are midwater predators and need a mixed diet of quality flake or pellets plus regular feedings of live or frozen crustaceans. As youngsters they tend to be a little dull, but fully grown Bedotia geayi are very handsome, with colourful fins and a sleek body. They generally ignore their tankmates, but may eat very small fishes. Bedotia geayi needs little salt, but demand hard, neutral to alkaline water. A specific gravity of around 1.005 is adequate.

Another commonly sold atherine is Telmatherina ladigesi , the Celebes rainbowfish. This is an active and beautiful fish that should is high on the list of desirable fishes for any aquarium. It has a neon tetra-like blue band within its clear body, plenty of yellow and black on the fins and large, bright eyes. Although small (7 cms or 3 inches) it does well in a spacious tank (over 60 cms, 24 inches, long); when their bright colours really shine. Although both sexes are lovely, the male has extended black rays to the anal and dorsal fins which it flutters to prospective mates. Keep in the same way as Bedotia geayi , offering plenty of live or frozen food to ensure bright colours.

This FAQ was compiled by Neale Monks from many sources, including the discussions on the brackishwater Aquarium mailing list. Comments, criticisms and corrections can be sent to the compiler for inclusion in subsequent versions. The list is maintained by P. Doug McKinney

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