Small and Unusual Brackish Water Fishes

Killifish

Note: Many thanks are also due to Doug Dame for his extensive additions to the section on American killifish.

There are very many killifishes suitable for the brackish water aquarium, although only a few are regularly traded in commercially. This is a shame, as killifish are small and colourful, and hardy enough to do well in most domestic aquaria. They are relatively straightforward to breed, although may need quite specific water conditions to spawn. Most species are distinctly territorial, and while they don’t require huge amounts of space each fish should be allowed enough space to set up a home patch without interfering with the other fish in the tank. 

Killifishes are most diverse in the tropical part Americas and Africa, especially in shallow or seasonal waters where other fishes are lacking. There are also killifishes in Asia, and the temperate parts of North America, Mediterranean Europe and the Middle East. Identifying species is not easy, and only a superficial review is made here. Many books have been published on keeping killifish in aquaria, but these tend to concentrate on the African and Asian species. For the European and American species you may need to refer to books on native fish faunas. There are also a number of killifish associations, some of whom have web pages. There are many advantages to belong to these associations beyond access to information, including the opportunity to get specimens of killifish not otherwise traded in commercially. One great feature of keeping killifish is that many species lay eggs which, if wrapped in damp moss or cotton wool, can be mailed around the world! In many cases it is also possible to catch specimens of native killifish yourself. As with all native fishes, check with your local authorities as to the legal restrictions on collecting in your area, and always collect responsibly. Some species are rare and protected in the wild, and these should never be collected, and with those species that are not protected, take no more than you really need and do your best not to otherwise disrupt the habitat from which you are collecting.

American Species 

The most widely traded brackish water killifish is the Florida flagfish Jordanella floridae. This is a medium sized killifish, growing to about 6 cm (2.5 inches) in length, and rather deep and stocky. The fish are very attractive with a complex pattern of red and pearl coloured stripes along the body overlaid with green or blue bands most obvious on the upper part of the flanks from the head back to the dorsal fin. The dorsal fin is also brightly patterned. Although both sexes share the same basic colouration, the males are especially colourful when in breeding condition. These fish occur in a wide variety of waters, not just brackish, so some care should be taken to allow the fish to adapt to the conditions of the aquarium. Otherwise they are active and hardy. As well as flake and small invertebrates, these fish should be provided with algae and other vegetable matter. Like many killifish, nibbling at algal growths ("aufwuchs") is an important source of food in the wild. Keep these killifish in a planted tank, but not too densely stocked since the males can be territorial. This is a subtropical fish that does best between 18 to 24° C (68 to 72°F). It can tolerate slightly warmer conditions though, and if kept too cold the males might not develop their otherwise impressive colouration. May be kept in freshwater or slightly brackish water, to SG 1.005. Since this is a fish naturally found in quiet waters, avoid using powerful electric filters and instead opt for something that produces a more gentle flow of water such as an air-powered sponge or undergravel filter. The closely related Yucatan pupfish Garmanella pulchra needs similar conditions, but is less tolerant of low temperatures and must be kept between 22-28° C (72-82° F).

The American killifish of the genus Cyprinodon, such as the sheepshead minnow Cyprinodon variegatus widespread along coastal North and Central America, are very characteristic of costal brackish and marine habitats and can often be found alongside livebearers such as mollies. Besides estuarine waters, Cyprinodon species can also be found in inland waters made saline by mineral-rich streams or high rates of evaporation, and also in hypersaline lagoons, where these fishes can be found in waters up to six times more salty than normal sea water. 

Unsurprisingly then, it is important to provide these fish with hard, alkaline water (pH 7.5 to 8) well buffered with coral sand or crushed shells placed in the filter. Most Cyprinodon require plenty of warmth and a rich growth of algae on which to graze: a temperature of above 25° C (77° F) is essential as is bright light to promote good algae growth but do provide some cover for the fish with floating plants or small caves (small flower pots are ideal). Avoid using materials, like driftwood, that might lower the pH. Although not as attractive as Jordanella, in breeding condition the males often becomes brighter and quite attractive. In the case of the sheepshead minnow, both sexes are a drab olive-brown most of the time, the male developing a bright metallic blue region across the upper part of the flanks when in breeding condition. Provided with the right aquarium the most attractive thing about these fish is their behaviour. Sheepshead minnows are active fish, and in the case of males territorial as well, and so do best in a species tank where they won’t be able to harrass other species. Males hold open water territories about 22 x 22 cm (9 x 9 inch) square, preferring sand or a mixture of sand and gravel over more complex bottom conditions filled with ornaments, bogwood or pebbles. They spend a great deal of time chasing one another out of their home patches. As such then, these fish would be ideally suited to a fairly spacious open species aquarium with floating plants rather than the more typical community tank, with some cover towards the edges for fishes to hide in but most importantly enough space for all the males to set up their own territories. There are numerous other Cyprinodon species that can do well in aquaria but these need to be collected from the wild as they rarely, if ever, turn up in aquarium stores. 

Another American killifish found in a variety of waters are those of the genus Fundulus. These fish have been widely studied by zoologists because of their remarkable ability to adapt to different water conditions from freshwater right through to hypersaline water more salty than the sea. The mummichog Fundulus heteroclinus is perhaps the best known. These fish are substantially larger than Jordanella or Cyprinodon, reaching as much as 15 cm (6 inches) in some cases. In shape they are streamline and rather like minnows without the upturned mouths of many other killifish. They are quite predatory, taking small insects and crustaceans mainly but will eat small fish and eggs if they can. Otherwise they are peaceful and should be mixed with other quite fish. In the wild they are commonly found with fish such as mollies Poecilia and Mollienisia. These make ideal companions in captivity, since they are of similar size and temperament but prefer the upper part of the tank, while Fundulus tend to swim close to the bottom. Being subtropical fish these fish do not need quite so much heat as tropicals, around 20° C (70° F) being adequate, perhaps dropping by a few degrees in winter. Closely related species include two similarly large but rather less easily maintained species, the longnose killifish, Fundulus similis, and the Gulf killifish, Fundulus grandis. These species are naturally found in marine or brackish waters rather than freshwater and this may be one reason why they have a reputation for being difficult to maintain and are much less commonly seen than the mummichog.

There are some other North American killifish worth trying out but as with many of the species mentioned here these will need to be collected as they are rarely traded. The diamond killifish, Adinia xenica, is a small (5 cm / 2 inch) omnivorous species that likes a deep aquarium with marine, brackish or hard freshwater (try to provide conditions as close as possible to those that the fishes were caught in). It is very pretty, with bright pearly white bands and almost diaphanous fins with a beautiful lacy pattern to them. The rainwater killifish, Lucania parva, is another small species that can be found in a variety of water conditions in the wild. Both these killifish do best in a mature tank and may need to be offered live foods at least initially. The very attractive gold-spotted killifish Floridichthys carpio is a medium sized killifish, up to 7.5 cm (3 inches) found in brackish and marine waters that resembles the sheepshead minnow in shape and requirements, but as the name suggests has a very pretty pattern of golden spots on the body and fins.

European & Asian Species

The European and Middle Eastern genus Aphanius is rarely traded but in many ways parallels the North American Cyprinodon in habits and maintenance. Some species of Aphanius are extremely colourful. An example is the lovely Aphanius mento in which the males are blue-black in colour with brilliant light blue spots. These fish should be snapped up when seen! In most cases the males are territorial and the fish should be kept in a large tank, around 80 cm (36 inches) long. 

The Asian killifish of the genus Aplocheilus such as the Ceylon panchax Aplocheilus dayi and the striped panchax Aplocheilus lineatus are among the commonest killifish traded. They are known as "panchax" after the genus Panchax to which many of these species were once assigned. They are found in a variety of waters and will adapt well to slightly brackish water with a specific gravity of up to 1.005. These are fairly large killifish, up to 10 cm (4 inches) in length. They are distinctly predatory, and can easily eat fish of male guppy size. Kept in a well planted tank they mix well with fish too big to eat, such as glassfish (Parambassis spp.), chromides (Etroplus spp.), and small spiny eels (Mastacembelus spp.) which all live in the same habitat.

Gobies

Like the rabbits in Richard Adams’ novel Watership Down, while the goby may have a thousand enemies, so long as he is alert and full of tricks his people will never fail. For while these small, unassuming fish may not seem much they absolutely dominate the brackish water environment. They are perhaps the definitive brackish water fishes, occurring wherever the sea reaches the shore or blends into rivers, streams and swamps, and you are as likely to see gobies in a cold North Atlantic sea loch as a tropical lagoon in northern Australia. At least a thousand different species have been described, undoubtedly there exist many more. Most live on the bottom, usually in burrows. In some cases the burrow is shared with varieties of shrimps or worms that excavate the burrow while the goby keeps lookout. Other gobies are cleaners, with flamboyant colouration to advertise their services. Still others can crawl out on land to feed on mudflats. All are characterised by fused ventral fins which form a sucker. It is believed that the ancestors of the gobies lived in mountain streams, where this served to stop them getting washed away, and only later did they return to the estuaries and coastal marine environment they are now supremely successful in. 

Bumblebee gobies, Brachygobius spp.

Note: Thanks to Naomi Delventhal for her help with these problematical fishes. She has provided a useful summary of bumblebee goby needs and breeding here.

Note: Bumblebees are often ignored by larger fish, perhaps because of their wasp-like colours, but some larger fish will eat them, including knight gobies. Choose tankmates with care. Thanks to CFC for this.

The Asian bumblebee gobies Brachygobius are probably the most widely seen non-marine gobies in aquarium stores. In the wild some species inhabit both fresh and brackish water while others are exclusively found in freshwater, but in captivity all seem to do well in slightly brackish water. They can also be kept in completely fresh water provided the water is not too soft and acidic. Although a pH of at least 6.5 is necessary, this still means they can be combined with neons, cardinals, dwarf plecs, Corydoras, and so on. Bumblebee gobies will also adapt to brackish water very readily, a specific gravity of around 1.005 being adequate for keeping these fish alongside brackish water species such as pipefish and mollies.

Unfortunately, many people are not successful at keeping these fish alive for long. Three rules need to observed. Firstly, do not expect them to take flake foods, they won’t. Some frozen foods (such as lobster eggs) are taken, as are live foods such as Daphnia and bloodworms. Secondly, they cannot compete with very active fish at feeding time. In large tanks, they may be successful at finding bits of food the other fish have missed, but in most community tanks these gobies can easily starve to death. Finally, bumblebees need good filtration and plenty of oxygen. They will not last long in tanks that are overstocked or inadequately filtered.

The best sort of aquarium for bumblebee gobies is thickly planted, though whether you use live plants or plastic is up to you. Useful plants include Java Fern, giant hygrophila Nomaphila corymbosa, and onion plants Crinum thaianum. Allow these plants to form a thick tangle, which will help the gobies to feel comfortable. Driftwood and blackwater extract can be used (provided the filter is buffered to prevent the pH becoming too acidic), and this will lend the water the peaty, dark quality characteristic of their swampy habitat. Decorate the bottom with large snail shells, such as those of apple snails.

To spawn these fishes they must be provide with some sort of cave or burrow (a small flower pot is ideal). The fish form pairs, and are markedly territorial. During the breeding phase, the males become much paler in colour, the black bands weakening considerably and may vanish altogether. The female is very round when filled with eggs. The addition of cooler, fresh water often triggers spawning. The female lays the eggs inside the cave and then leaves the male to guard the eggs and raise the brood. The fry swim in the open water at first and will need tiny live food (infusoria) at first, graduating on to newly hatched brine shrimps. After a few days the fry settle down onto the bottom and swim rather less. 

There are a number of species of bumblebee goby, found in fresh and brackish water conditions, some of which are imported very regularly, primarily Brachygobius doriae, but also Brachygobius sabanus and Brachygobios nunus. Identifying these fishes without being able to place them under a microscope is notoriously difficult. Up to ten will do well in an aquarium as small as 20 litres (5.5 gallons), and the larger the group, the less aggression between individuals tends to be.

Many aquarium books w

ill refer to Hypogymnogobius xanthozona, a very rare species that is not commercially collected or traded (there are in fact very few specimens even in museum collections). Where this name is used in the aquarium literature, it is safe to assume that one of the Brachygobius species is actually being referred to.

Violet gobies, Gobioides and Odontamblyopus spp.

Quite widely sold in the USA is the violet goby Gobioides broussonnetii, a large eel-like goby on the Atlantic coast from South Carolina through to northern Brazil. In Europe other species are more often seen, including Gobioides peruanus from South America and Odontamblyopus rubicundus from Southern Asia. True Gobioides broussonnettii have small, mudskipper-like eyes at the top of the head and a series of dark vertical bands running along the flanks. Gobioides peruanus has much fainter bands and they are only really obvious close to the head. Odontamblyopus spp. have virtually no banding and have tiny small eyes set further down the head. The pectoral fins also have hair-like extensions that are used while feeding.

All these fish need a soft substrate to burrow into as well as a large tank proportionate to their size. They are territorial, but they do not seem to do any harm provided each fish has someplace to hide. PVC tubes are inexpensive and widely used for this, but otherwise ordinary aquarium ornaments, bogwood, rockwork, or plants will do fine. They are bottom feeders and sift the substrate to capture small animals such as shrimps and worms. Frozen equivalents work well, along with catfish pellets. They do eat some algae as well, scraping it off with their small but sharp teeth.

While violet gobies are naturally found in freshwater, brackish and marine environments, brackish water with a specific gravity of at least 1.005, and preferably 1.010, is necessary for long term health in the aquarium. Otherwise, these fish are not difficult to keep and they are usually considered to be quite hardy animals.

Knight goby, Stigmatogobius sadanundio

An Asian goby often seen is the knight goby, Stigmatogobius sadanundio. This is found throughout South East Asia. Although it only needs little salt (specific gravity of 1.001 to 1.005 is fine), it cannot adapt to completely fresh water. Of moderate size, 8 cm (3.5 inches) it is peaceful and can be combined with fishes that stay in the middle and upper part of the tank. May take flake, but crustacea, worms and chopped mollusc meat should be a regular part of the diet. Also relishes green leafy algae, which may be substituted with blanched lettuce tied to a weight such as a pebble.

White-cheeked goby, Rhinogobius duospilus

An Asian goby often seen is the knight goby, Rhinogobius duospilus, commonly sold as Rhinogobius wui, is a hardy subtropical species that does well in small aquaria. It does well in freshwater and brackish water conditions (SG around 1.005) and gets on well with bumblebee gobies, knight gobies, and other small, peaceful species. Because it is a subtropical species it does not appreciate temperatures above 24° C (75° F) for extended periods. If you must keep it in a tropical aquarium, ensure that the tank is not overcrowded and use plenty of aeration to keep the dissolved oxygen concentration high. It is a lively species that readily eats bloodworms, crustacean eggs, small pieces of shrimp, and Artemia. It will not eat flake.

Freshwater gobies, Awaous spp.

Note: Thanks to Bruce Hansen and Naomi Delventhal for the information on these gobies. Naomi has written a detailed article on the care and breeding of these fishes for Gobiidae.com

The freshwater gobies of the genus Awaous appear from time to time and can be good aquarium fish. There are various species, Awaous flavus from the tropical South American coastline being the most commonly imported. It inhabits brackish and fresh waters and requires slightly acidic to slightly alkaline, moderately hard water to do well. In Europe, the scribbled or pearl goby Awaous grammepomus from South East Asia and New Guinea is more frequently seen, though it requires much the same conditions. An Australian species, the Roman nose goby, Awaous acritosus, also does well in freshwater aquaria.

These are medium sized gobies, typically 8 to 15 cm (3 to 6 inches) in length, and so need a fairly large aquarium. These gobies are inveterate burrowers, and a soft, sandy substrate is absolutely essential. Like spiny eels and flounders they will bury themselves completely if they can, especially if they feel threatened. Awaous feed in the same way as the eartheater cichlids, staying close to the bottom and sifting mouthfuls of sand for insect larvae, worms, and other small invertebrates. In captivity they will happily take frozen foods and small prawns as well as various live foods; they also need some plant material, either soft algae or a substitute such as blanched lettuce leaves or defrosted frozen peas.

Awaous gobies are widely distributed and found in both the Old and New World, and as adults at least are tolerant of a wide range of salinities, although in most cases they are found in fresh or only slightly brackish water. Reproduction is different to most of the commonly kept gobies in that while spawning does take place in freshwater, with the male guarding the eggs inside a small cave, after hatching the larvae drift downstream to the sea, where they pass through a planktonic stage. There they feed and grow, and if they are fortunate the ocean currents will bring them to some body of brackish water such as a river estuary or mangrove where they will metamorphose into their juvenile form. These little gobies will then swim upstream into their coastal streams they favour. Undoubtedly this planktonic stage accounts for the very wide distribution of these fish, allowing successive generations to hop from island to island or along the coastlines of continents much more successfully than the adult gobies could under their own steam. But it also makes them difficult to raise in captivity because the fry will not accept the usual foods supplied to young fish by aquarists.

Glassfish

Warning! Periodically, glassfish are sold which have been injected with brightly coloured dyes. Besides being very cruel, this process weakens the fish and may make it more susceptible to disease. Please don’t buy these dyed fish. 

Glassfish are small perch-like fish which are found in salt and brackish water around the coastline of tropical Asia and Australia. They are laterally compressed perch-like fishes that are remarkable for their transparent bodies. Several species are offered to aquarists, but actually identifying these species is rather difficult. At least three species in the genus Parambassis that are traded fairly regularly as the ‘common glassfish’ or ‘Indian glassfish’, but of these Parambassis ranga appears to be the most frequently seen.

Glassfish are not easy to keep for several reasons. Firstly, they are very picky about their food, and while they may sometimes take dried foods this is rarely the case with newly imported specimens, and even after months in captivity most will only take live or frozen invertebrate foods. Frozen bloodworms, mosquito larvae, and lobster eggs are readily eaten, and once settled down you can try a variety of other small, meaty foods such as shrimp eggs and small pieces of shrimp or white fish.

The second problem is that none of the glassfish is really hardy in the sense of being tolerant of rapid changes in water chemistry or poor filtration. When introduced into immature aquaria they often sicken and die rather quickly, although the aquarist may be warned that something is wrong when these normally silvery or transperant fish take on a milky hue.

Finally, it is debatable whether or not these are truly brackish water fish. In the wild the species offered to aquarists normally inhabit fresh rather than salty water, but by the time these fish arrive in your local tropical fish shop they will invariably have been maintained in slightly brackish water for several weeks. At least some species appear to do well in slightly brackish water, and most aquarium books recommend keeping them in aquaria with a specific gravity of around 1.002 to 1.005. Even so, it is as well to be aware of the fact that these fish actually prefer neutral, soft to moderately hard fresh water. Glassfishes are sensitive to low temperatures, and will need to be kept at around 25° C (75° F) outside of breeding.

Otherwise these fish do not pose any major problems. Most are relatively small (typically around 4 to 8 cm in length), completely peaceful, schooling fish. They do best in planted tanks and prefer a mix of bright and shady spots and enjoy a strong water current. Good tankmates include gobies, peaceful livebearers, and halfbeaks. Some species have bred in captivity. Raising the temperature up to 28° C (84° F) and allowing the tank to get some natural sunlight in the morning appear to be most reliable triggers. The eggs are scattered among plants, and although generally ignored by the parents it is probably best to remove them just in case. The eggs are prone to becoming fungused, but this can be prevented by use of an antifungicide. Raising the fry is difficult because they are very small and can only take infusoria at first.

The most commonly seen glassfish are Parambassis ranga, Parambassis lala, and Parambassis siamensis, all of which are offered simply as ‘glassfish’. In breeding condition, male Parambassis lala have blue-white edges to their anal and dorsal fins while those of Parambassis ranga and Parambassis siamensis are off-white or grey. Otherwise, all these fish are wonderfully transparent fish and tricky to tell apart. These best indicator is body shape and markings. Parambassis siamensis have rather elongate bodies (they are about three times long as they are deep) while Parambassis lala and Parambassis ranga are much more diamond-shaped (about twice as long as they are deep). Parambassis lala and Parambassis ranga can be distinguished by their markings: Parambassis lala have three vertical bands running down the flanks while Parambassis ranga has at most a single dark spot behind the eye.

A giant among glassfish is Parambassis wolffii, which can easily reach a length of 20 cm (8 inches) or so, though once fully grown is no longer transparent but a rather plain steely-grey in colour. This is a very rarely traded species: in twenty years I have only ever seen a single adult of this species offered for sale, though juveniles may get mixed up in batches of common glassfish rather more frequently. Another large glassfish is the hump-headed glassfish Parambassis pulcinella. This species was unknown in the hobby until very recently, but it is now exported from Thailand and Burma fairly frequently. Both Parambassis wolffii and Parambassis pulcinella are unquestionably freshwater fish and should not be kept in brackish water aquaria.

Another very rare glassfish is the filament glassfish Gymnochanda filamentosa, similar in size and habit to the common glassfish but with the males possessing greatly extended anal and dorsal fin rays. They need soft, acidic water conditions similar to those of discus and tetras. Obviously this fish is unsuitable for brackish water aquaria.

Pipefish

Note: There is an excellent scientific paper on keeping pipefish written by R. A. Burhans of the Scripps Institute. For anyone interested in these fish, it is essential reading, and can be downloaded here.

Pipefish are relatives of the seahorses and share many of the same problems when it comes to life in the aquarium. They are slow-moving, rather shy fish that find it difficult to compete with other fish at feeding time. Moreover, while they can ultimately be trained to take dead foods such as frozen mysis, to begin with you will need to supply them with a mixed diet of live foods, including brine shrimps, Daphnia, mosquito larvae, and bloodworms. Because of the plates that cover the body of these fish, it is difficult to tell whether they are well-fed or not, and it is entirely possible that specimens offered for sale at your tropical fish store have not eaten properly for weeks.

All pipefish are sociable and should not be kept alone. When happy, they will breed in captivity, and like seahorses, it is the male that carries the eggs in a special brooding pouch.

Enneacampus ansorgii is sometimes sold under the name Syngnathus pulchellus and is known as the African freshwater pipefish. It is a small fish, reaching a length of no more than 15 cm (6 inches). Both sexes have brick-red to orange bellies. It needs clean, oxygen-rich water but is not especially picky about salinity provided the water is hard and not acidic. It probably does best with a little salt added though, for a specific gravity of 1.002 to 1.005. This is a relatively benthic species, and will sometimes rest on the substrate or among plants.

Microphis brachyurus aculeatus (also known as Microphis smithi in older books) is a large species, up to 20 cm (8 inches) long, and is comparatively robust and easy to keep. Besides small insects and crustaceans, it will also eat very small fish, including livebearer fry. In the wild, this fish can be found in fresh, brackish, and marine waters, so can adapt to a variety of conditions. Thse pipefish are active swimmers and like to swim in the upper level of the tank beneath leaves and floating plants.

Livebearers

Although the ability to produce live young (rather than eggs) is found in many groups of fishes, the family Poecilidae is so specialised for this mode of reproduction that the group is usually referred to simply as the ‘livebearers’. Females are generally larger than the males, and often quite drab in colouration. The males have bright colours which they use to attract the females. When they mate, the male uses the specially modified anal fin, which is shaped like a tube, to squirt sperm into the female. In many cases the female can use the sperm up a bit at a time, allowing her to produce a series of broods after just one mating.

Livebearers do not form lasting pairs; after mating the male immediately seeks out new females. For this reason it is generally considered best to either the fish in single sex tanks except for mating, or else to ensure females outnumber by two to one or more. Otherwise the persistent attentions of the males stress the pregnant females and can cause miscarriages.

Limias, Limia spp.

Several species of Limia occur in brackish water, usually in slow-moving streams and pools. They are primarily algae-eating fish though they also eat insect larvae and other small animals. In aquaria they are hardy, easy to breed, non-aggressive and generally very easy to keep. Limia nigrofasciata is known as the humpbacked limia on account of the deep body that mature males develop. They also have speckled black dorsal fins. The females are more streamlined in shape. Both sexes are yellowy-brown in colour with vertical black bands and yellow fins. Ideally suited to low salinity brackish water aquaria around SG 1.005.

Guppies, Poecilia reticulata

All guppies do very well in low salinity brackish water aquaria, and ‘feeder guppies’ and wild-caught guppies can be slowly acclimated across a few weeks to salinities as high as that of normal seawater. Fancy guppies are less tolerant, and often do not do well above SG 1.010.

Platies and Swordtails, Xiphophorus spp.

Swordtails rarely occur in brackish water in the wild, and platies hardly at all in their natural range, but both will adapt to slightly saline conditions up to about SG 1.005.

Mosquitofish Gambusia spp.

Mosquitofish such as Gambusia holbrooki and Gambusia affinis are tolerant of brackish water at least as saline as SG 1.005 and likely to SG 1.010 with careful acclimation. Lab specimens of Gambusia affinis have been acclimated to full seawater when adjusted to such conditions over a course of three days. But their value as aquarium fish is limited because they are not particularly colourful and are also very aggressive and nippy. Recommended for advanced aquarists interested in infrequently kept livebearers rather than community fish.

Pike livebearers Belonesox belizanus

Belonesox belizianus are very salt tolerant and will adapt to any brackish water aquarium. They are peaceful towards fish too large to be swallowed (for example adult scats and monos) but they will attempt to eat anything smaller than they are, including their own kind. The main problem for the aquarist is that they are reluctant to take anything other than live foods. Wild-caught specimens normal only accept live fish, large insects and river shrimps. Tank-bred specimens may be more amenable to frozen foods: check with the retailer or breeder.

Livebearing Halfbeaks

Livebearing halfbeaks (now classified as the family Zenarchopteridae) are related to the marine halfbeaks, but differ in their mode of reproduction. While they are livebearers like guppies and mollies, they are considered to be more difficult fish to keep. They need a tank with plenty of open swimming space and a steady but not excessively turbulent current. They are nervous, flighty fish that will jump when alarmed. For this reason, the tank should be kept covered and aggressive tankmates avoided. Like needlefish, they can harm themselves by swimming into the glass when frightened. Floating plants help them to feel more secure, and a few tall plants around the edge of the tank will reduce the chances of accidental collisions with the glass. Also like needlefish, they do not tolerate sudden changes in water chemistry particularly well. Once settled in though, halfbeaks at least are fairly robust and have much to recommend them as aquarium fish for more experienced fishkeepers wanting something small but unusual to keep and breed.

Halfbeaks are territorial, aggressive fish that constantly squabble, chasing one another around the tank and sometimes engaging in quite alarming fights. Males are the most aggressive, but females are only marginally less short tempered. Halfbeaks completely ignore other fish, and while they might eat small fish like livebearer fry, they are not particularly predatory and make good community tank residents. Needlefish are peaceful, schooling fish best kept in small groups. They are of course predatory and well able to eat small fish, but otherwise get along well with peaceful catfish and gobies of similar size.

Halfbeaks appreciate live foods including Daphnia, bloodworms, and brine shrimp, but in the wild all species are at least somewhat herbivorous. A diet containing vegetarian flake and frozen bloodworms will suit most species very well. Almost any small live foods are taken, including daphnia, brine shrimp, and mosquito larvae. Crustacean eggs are very popular, either frozen lobster eggs (sold for feeding marine invertebrates) or fresh shrimp eggs taken from coldwater shrimp bought at the fishmongers (in the UK at least, the shrimp have these eggs only in winter and spring). Halfbeaks also enjoy live insects, such as fruit flies and bluebottles.

Wrestling & silver halfbeaks

A variety of species are sold under this name, primarily Dermogenys pusilla, Dermogenys sumatrana, and Dermogenys siamensis. Telling them apart is not easy. These fish are relatively small, growing to between 4-7 cm (1.5-3 inches) in length.

Males Dermogenys are notoriously aggressive towards one another, and will fight. Except in a really big aquarium, or in ‘colony’ tanks containing dozens of specimens where aggression is spread out, it is best to keep just a single male alongside a group of females. Male fish are smaller, more colourful, and have a distinctively shaped anal fin with bent fin rays.

Dermogenys spp. are excellent halfbeaks for the beginner. They are hardy, tolerant of a wide range of water conditions, and easy to breed. The come from India and South East Asia and live in a variety of waters from soft and acidic through to slightly brackish (up to around SG 1.005 or so). Gestation takes about a month, and the female produces around ten to twenty offspring. She will miscarry if disturbed, and the prematurely born fry are difficult, probably impossible, to rear. On the other hand, properly delivered fry are hardy, grow relatively quickly, and will accept various small live foods as well as finely ground flake.

Celebes halfbeaks

Nomorhamphus liemi liemi is the species usually sold as the Celebes halfbeak, but a number of other species, such as Nomorhamphus ebrardtii, are sometimes included in batches of Celebes halfbeaks.

N. liemi liemi is quite a big fish, females getting to about 10 cm or so, though males are a bit smaller. They are brightly coloured, sporting red, blue, and black patches on their fins. Females have virtually no beak at all, while makes have a distinctively curled beak that forms a goatee-like structure. The other species typically lack the blue having differing amounts of red or yellow in their fins, if any at all, and unlike N. liemi liemi usually have straight beaks. Identifying these unknown halfbeaks is difficult.

These fish naturally inhabit freshwaters throughout South East Asia and will do best in slightly acidic, soft to moderately hard water. They can be adapted to very slightly brackish water as well (SG less than 1.003) but few species naturally inhabit such conditions and breeding them seems to be easier in soft water. The exception is Nomorhamphus ebrardtii, a species that does indeed live in brackish water in the wild and does not thrive when kept in soft and acidic water conditions. Nomorhamphushalfbeaks are fairly robust when settled in, and breed quite readily. Gestation is about a month or so, and a small brood (around a dozen) fry are produced. These are large and grow very quickly, and will feed readily on various live foods such as small daphnia.

River halfbeaks, Zenarchopterus spp.

Zenarchopterus spp. halfbeaks are true brackish water fish that will do well in either brackish or marine conditions. Some species seem healthy enough in freshwater, too, at least for short periods. Zenarchopterus buffonis is one species that is periodically traded. It is a big fish, around 20 cm (8 inches) when mature, and can easily be mistaken for a small needlefish. It is a schooling species and no aggression has been seen between specimens. Quite the reverse in fact: these fish are very nervous and cannot be mixed with anything aggressive or predatory. Best kept in their own aquarium. Nothing is known about their reproductive biology. Wild fish feed primarily on algae, plankton, and small invertebrates.

Bearded halfbeaks, Hemirhamphodon spp.

Various species of Hemirhamphodon are sometimes sold in aquarium shops, most frequently Hemirhamphodon pogonognathus. Though these are beautiful fish, they are not normally found in brackish water, requiring instead, clean, peat-filtered, very soft (near-zero hardness), and fairly acidic (pH 4.5-5.0) water to do well.

Blennies

(See also the section on coldwater blenny species.)

Blennies are small, goby-like fishes that are found primarily in shallow marine habitats, and are especially common in the intertidal and subtidal zones. Relatively few are traded as aquarium fish. One new species in aquarium stores is Omobranchus zebra, a 6 cm (2 inch) fish that requires strongly brackish (SG 1.010) to fully marine conditions for long-term care. It will not adapt to completely fresh water. It is usually traded as the ‘striped blenny’ or ‘zebra blenny’.

Not much is known about its preferences in aquaria, but a mixed diet with plenty of small crustaceans and worms is useful. By analogy with other blennies, these fish are likely to be intolerant of immature aquaria and poor water quality. The water should have a high pH (at least 7.5), high hardness, and plenty of oxygen. Water temperature is not critical, but be aware that in warm weather (or overheated aquaria) the oxygen concentration will fall and these fish do seem to suffer.

Some specimens, presumably dominant males, seem to very territorial towards conspecifics to the point where they have been reported to kill other blennies in the tank with them. So in small aquaria is probably best to keep one to a tank. In larger tanks it may be possible to keep them either in large groups so that aggression is spread out, or else in small groups but with each fish having a clearly defined territory, such as an artificial cave of some type.

Spaghetti Eels (Moringua spp.)

Spaghetti eels are closely related to moray eels anmd strongly resemble them in terms of overall shape, but tend to be thinner and equipped with more delicate jaws. They are predominantly marine fish and are found throughout the Indo-Pacific region in a variety of coastal marine habitats. However, a few species may be found in estuaries and rivers, and are consequently of interest to brackish water fishkeepers.

Spaghetti eels are non-territorial, and in fact rather gregarious, so aquarists should try to keep them in groups of three or more specimens. They like to dig, and are best kept in tanks with a sandy substrate. As with most eels, spaghetti eels prefer shady tanks with lots of hiding places, and in brightly lit tanks will rarely swim about during the day. In fact even in optimal conditions they will prefer to stay buried in the substrate most of the time.

Spaghetti eels are predators, but they take very small prey, primarily insects, worms and other small invertebrates. So while they may consume livebearer fry, they can otherwise be considered good community fish. Indeed, the main thing is to avoid mixing them with anything so large or aggresive the spaghetti eels would be at risk of being nipped. Their diet should be based primarily on live or wet-frozen foods such as bloodworms, mosquito larvae and tubifex.

The species most often traded is Moringua raitaborua, the purple spaghetti eel. It gets to a maxium length of around 40 cm and varies in colour from pinkish-gold to purple. It is found in fresh, brackish, and saltwater environmental. It is an adaptable species that does very well at middling salinity levels, a specific gravity around 1.010 being ideal.

Glass Eels and Rice Paddy Eels (Pisodonophis spp.)

The family Ophichthidae contains a few hundred mostly marine eels that are peculiarly well adapted to burrowing through silt and sand. A few species enter brackish and freshwater habitats, and at least one species, Pisodonophis boro, known as the rice paddy eel, has been traded as an aquarium fish.

Pisodonophis boro is reported to reach an adult length of up to 100 cm, but aquarium specimens are likely to remain somewhat smaller. It is primarily found in shallow marine and brackish water habitats but sometimes swims into adjacent freshwater areas, and it is reported to spawn in rice paddies. Wild fish are nocturnal and feed mostly on small fish though it has also been reported to eat small crabs, specifically fiddler crabs. Pisodonophis boro is greenish-brown in colour, has a very thin snake-like shape, and remarkably reduced fins. Pisodonophis boro is able to burrow into the sediment either head-first or tail-first, but has relatively poor eyesight and likely hunts primarily by smell.

Rice paddy eels have not been commonly traded and little is known about their care. Basic maintenance is likely very similar to that of spaghetti eels, as described above, though allowance should be made for their potentially larger size and more piscivorous nature. A mixed diet of insect larvae such as bloodworms, earthworms and river shrimps will likely work well, and settled specimens should adapt to taking wet-frozen foods of all kinds.

Since Pisodonophis boro are burrowing fish, the aquarium must contain a soft, sandy substrate. River sand or smooth silver sand would be best; a little coral sand might be added to raise the pH and hardness should that be required. Salinity is of secondary importance, and something between SG 1.005 to 1.015 at 25 degrees C should suit them well.

Because this species has only very recently appeared in the trade, little is known about how well adult Pisodonophis boro behave in community tanks. Juveniles at least appear to be peaceful, even gregarious. However, given its size and predatory nature, anything small enough to swallow whole will likely end up being eaten, and adults would probably have to be mixed with robust fast-moving midwater fish such as monos and scats.