Ask the WWM Crew
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While members of the order Beloniformes are not widely kept as aquarium fish, a few species are traded regularly enough to have become fixtures in the hobby. Five families are included within the Beloniformes, of which two, the Exocoetidae (flying fish) and the Scomberesocidae (sauries) are of no importance as aquarium fish. Incidentally, the name of one genus of flying fish, Exocoetus, may be more familiar to some readers as the source of the name 'Exocet' given to the anti-ship missiles used with devastating effect during the Falklands War.
The three remaining families are the Hemirhamphidae, Belonidae, and Adrianichthyidae. The first of these, the Hemirhamphidae, includes the halfbeaks, several of which have become quite popular as aquarium fish. The Celebes halfbeak, Nomorhamphus liemi, is perhaps the most frequently seen, but the wrestling halfbeak, Dermogenys pusilla, is not difficult to find either. One or two additional species turn up from time to time, but have so far failed to establish themselves in the hobby.
Looking more like garpikes than a halfbeaks, the needlefish are predominantly marine in distribution, and anyone who has been mackerel fishing on the South Coast in summer has quite likely reeled in a specimen or two of the North Atlantic needlefish, Belone belone. This handsome fish is notorious for having emerald green bones, which do tend to put people off this otherwise very tasty fish. There are several fresh- and brackish water species, but only one, the South East Asian species Xenentodon cancila, is regularly imported.
The joker in the pack is the family Adrianichthyidae, which includes the medakas (or rice fish) of the genus Oryzias. These fish are strikingly killifish-like, and for many years they were indeed classified as killifish. To be fair, while their genetics might prove them to be more closely related to halfbeaks and needlefish than killies, they don't look very much like them. Where the other members of the Beloniformes have elongate bodies with narrow jaws often extended into beaks, the medakas have laterally compressed bodies with small, upward-pointing mouths. Although not very commonly seen, the medakas are interesting fish that are generally hardy and easy to breed, and being small and completely peaceful, make excellent fish for the community aquarium.
Like most of the other members of the Beloniformes, halfbeaks are elongate fishes with long, narrow jaws that spend most of their time swimming close to the surface of the water. Most halfbeaks are marine and feed on plankton and fragments of vegetation, particularly seagrasses, but the freshwater species are more predatory, and prefer insects and other small aquatic animals. In captivity they will accept live foods like fruit flies, Artemia, and mosquito larvae, as well as frozen bloodworms and flake foods.
My school of Celebes halfbeaks seem especially fond of shrimp eggs, and in fact I find these work well for all sorts of fish that are otherwise a bit slow at feeding time, including glassfish and bumblebee gobies. If you buy some unshelled coldwater prawns from your local fishmonger during spring and summer, the chances are that you'll find many of them 'in berry', that is, with the eggs underneath the tail. These eggs can be scooped out and laid flat on some aluminium foil and frozen for use throughout the year. Halfbeaks are often a bit underweight after a few weeks in an aquarium store, but shrimp eggs are rich in fat and protein and quickly help them recover. Don't use them as the staple food though; halfbeaks really need a varied diet, and if you can get them to take a good quality flake food, that will be the best way to ensure they get all the vitamins and minerals they might not otherwise get from things like shrimp eggs or Artemia.
Halfbeaks are paradoxical when it comes to water quality and parameters. On the one hand, some seem to be indifferent to lapses in filter efficiency, and I've used Nomorhamphus liemi to mature new aquaria without any problems. They aren't bothered by pH or hardness levels either, provided the extremes are avoided.
So far, so good, but the downside is this: halfbeaks have virtually no tolerance for sudden changes in water chemistry, even if the change is intended to be a beneficial one. Once you've bought some halfbeaks, you want to get them home as quickly and as gently as possible, and avoid transporting them on days that are exceptionally hot or cold. Carefully pierce the bags a few times with a needle and then pop the bag into the aquarium for at least 30 minutes before releasing the fish. The holes will let water move between the bag and the aquarium, helping to balance out the temperature and more importantly get the halfbeaks used to the salinity, pH, and hardness of your aquarium. Incidentally, this holds true for things like water changes, which are much more safely done in small but frequent batches (definitely no more than 10% at any one time).
If you don't let them adapt gently to the new aquarium, chances are that some, even all, of your halfbeaks will die. The symptoms of this 'water shock syndrome' varies, but a gradual darkening of the body, an upwards flexure of the spine, and rapid breathing all seem to be fairly typical. Sick fish loose condition quickly, and invariably die within a few days. Although some halfbeaks naturally inhabit soft and acidic waters, in aquaria it is probably best to keep them all in moderately hard, slightly alkaline water. This doesn't seem to be detrimental in any way, and the salts in the water will act as buffers against any sudden changes in pH.
There are a couple of other issues with halfbeaks that need addressing. The first is decorating the aquarium. While halfbeaks show no interest in things like caves or bogwood, they do appreciate plants at the surface. Floating plants are an obvious choice, but long-leaved plants like Vallisneria that cover the surface also work well. Plants serve a variety of functions in the halfbeak aquarium. They provide cover, helping the fish feel secure, and surface plants will also inhibit the tendency of halfbeaks to jump when alarmed. Plants also give the baby halfbeaks somewhere to hide; although not particularly predatory, halfbeaks have been known to eat their offspring. Finally, plants on the sides and back of the tank provide visual cues to the boundary of the aquarium, helping the halfbeaks to avoid smashing themselves against the glass.
The other issue is social behaviour: do they make good community fish? Halfbeaks certainly are peaceful and don't do things like dig up plants or nip at the fins of other fish. So in theory, they can make excellent community fish. But their companions should be chosen with caution. Fish that are apt to be aggressive or boisterous (like cichlids or blue gouramis) would not work well with halfbeaks. Halfbeaks can also be a bit boisterous among themselves. Both males and females fight with one another, and while they should always be kept in a group, it is just as important to make sure each fish has some space. Males in particular hold 'patches' for short periods, and will drive off any other male who comes too close. These patches are usually close to the leaves of some plant, so it's best to make sure that there are lots of floating plants and leaves so that each fish can stake its claim. All halfbeaks like to spend at least some of the time swimming into a strong current, but they also like to rest in relatively still areas as well. Having two or more filters (or at least additional airstones or pumps) can be a good way to provide a mix of still and moving water.
Halfbeaks are livebearers, but unlike guppies or mollies, breeding them represents a significant challenge. There are several factors to consider. The first is that these are relatively nervous fish, so for breeding purposes you either want to keep them alone or with very peaceful fish that will stay away from them (bumblebee gobies, for example). Secondly, water conditions are important, which in the case of Dermogenys pusilla means slightly brackish, rather than fresh, water. Nomorhamphus liemi appears to breed most readily in soft, slightly acidic water, but has been known to breed in moderately hard, slightly alkaline water as well. Finally, the fish will need to be conditioned well beforehand, and this means offering them live foods such as fruit flies and insect larvae or failing that good quality frozen substitutes.
The fry are quite big, around 2 cm in length, and though the adults will eat them, they are not very effective piscivores and so in a planted tank enough will survive long enough for the aquarist to find them and if necessary remove them to another tank. Do bear in mind that the fry are just as sensitive to changes in water chemistry as the adults. With both species of halfbeak, gestation takes about a month and a half, and broods are rather small, often around a dozen or so offspring at any one time. The fry are large enough to accept finely divided flake food and newly hatched Artemia.
There are several other halfbeaks that turn up very occasionally, but all require much the same thing as the species described above. Dermogenys pusilla in particular is quite probably substituted with different subspecies depending on where the shipment comes from. A very rarely seen halfbeak is Hemirhamphodon pogonognathus, the thread-jawed halfbeak, which has a very long lower jaw tipped with a distinctive 'beard'.
The Asian freshwater needlefish Xenentodon cancila is in some ways a scaled-up version of the halfbeaks. Like the halfbeaks, it appreciates a roomy, well planted aquarium without too much clutter and a fairly strong current. Also like the halfbeaks, this fish has a reputation for being delicate primarily because it handles sudden changes in water chemistry very badly. But unlike the halfbeaks this is a large, predatory fish. Adults can easily polish off fish as large as swordtails.
Having said this, like many other specialised piscivores (garpike and pike cichlids spring to mind) these fish are otherwise very quiet, and need to be kept either by themselves or with other peaceful species. Fish that stayed on or close to the bottom would probably be the best bet, such as loricariid catfish, peaceful cichlids, and large sleeper gobies. Anything that swims in the midwater and is either very active or overly curious is likely to stress these fish, so things like silver sharks and tinfoil barbs are best avoided. Needlefish are sociable, and do best in groups of three or more, and all things considered it is probably best to keep a small school alone or perhaps with one or two catfish.
One reason needlefish have never become popular is that they really only show much enthusiasm for live food. In the wild they primarily eat large insects and crustaceans, and things like river shrimps and crickets will certainly be accepted. However, most aquarists keeping these fish prefer to offer them small live fish, presumably because they don't realise that crickets, shrimps, mealworms, and earthworms are just as easy to obtain (not to mention a good deal cheaper). Moreover, feeding these fish on invertebrates is not only closer to their natural diet but greatly reduces the risk of transferring parasites. Adult needlefish are gorgers: they will eat lots one day, and hardly anything the next. This is quite normal, and actually a lot like many other large predatory fish. Take care not to overfeed them! What goes into a fish comes out eventually, and if you overfeed them this can put a mighty strain on the filter.
Needlefish rarely, if ever, go for flake food or pellets, and even frozen foods don't seem to be readily accepted. Dedicated aquarists could try employing the same tricks with needlefish as work well with marine fish like morays and lionfish, namely, tying thawed lancefish to cotton and then dangling the food in front of the fish until the needlefish bites. Some people have successfully weaned them onto dead foods, and this makes the aquarist's life a lot simpler.
Bearing in mind that adults are 30 cm in length, you'll need a tank at least 50% wider than that for them to be able to turn around, let alone swim freely in. Bottom line, if you want a school of these fish, you'll need an aquarium at least 60 cm wide and 150 cm long. Depth, on the other hand, hardly matters at all. There is probably some sense to using a deep tank but only partially filling it with water: even more than with halfbeaks, these fish are given to jumping when alarmed, and a thick layer of floating plants as well as some space between the top of the water and the hood will go a long way to mitigating this. If they jump and hit something, needlefish often damage themselves, and injured fish seem to be very prone to fatal secondary infections. One thing to bear in mind with needlefish is that the more you can avoid startling them, the longer they will live. This is especially important with regard to aquarium lighting, which needs to be arranged so that the tubes (if there is more than one) come on one at a time, and that when the lights are turned off the room is kept lit for a while so that the fish have some 'twilight' to settle down by before the room goes completely dark.
Breeding in captivity is extremely uncommon, primarily because not many people keep these fish in groups and in tanks big enough for them to feel comfortable. Needlefish are egg layers rather than livebearers, the females scattering the eggs among the plants and afterwards taking no interest in them at all. The resulting fry are a bit smaller than baby halfbeaks but are still able to take newly hatched Artemia and straight away. Juveniles can be raised on virtually any appropriately sized live food.
Needlefish are sometimes sold as brackish water fish, and it is true that a little salt in the water does seem to have a therapeutic value, particularly with newly imported fish. But in the wild these fish are only rarely found in brackish water, and are far more common in soft, acidic conditions. Mimicking this is probably essential to breeding, although removing the salt may make them more sensitive to bacterial and fungal infections. All in all, needlefish are difficult fish that can really only be recommended for advanced aquarists.
Medakas, or ricefish, are oddballs among the Beloniformes, having nothing obviously in common with the others members of the group. They aren't particularly streamlined, don't have elongated jaws, and aren't fast swimmers or accomplished jumpers. But recent studies of the genes of all these fishes appears to show that they are quite closely related, despite the fact medakas look much more like killifish than anything else.
Compared with halfbeaks and needlefish, which are fairly demanding fish as far as aquarium maintenance goes, medakas are extremely easy to keep and breed. They have in fact become important laboratory fish (an aquatic equivalent of the white rat!) thanks to their minimal demands, rapid growth rate, and willingness to breed in captivity. The medaka most commonly seen is Oryzias latipes, the Japanese ricefish, a coldwater species that will do perfectly well in ponds during the summer. Tropical species seen from time to time include Oryzias javanicus and Oryzias celebensis, but these tropical species are notably more delicate than the coldwater ones.
Medakas breed in an extremely unusual way. Females exude their eggs into the milt shed by the male, but the eggs remain connected to the female by threads, resulting in something like a bunch of grapes. These eggs are then brushed off on plants over the next few eggs, one at a time. Once they hatch, the fry can be raised in the same way as killifish fry, with powdered or liquid fry foods augmented with newly hatched brine shrimp. Some algae in the aquarium appears to be beneficial as well.
The Beloniformes are not major players in the aquarium hobby like the catfish or the cichlids, but they do include some very appealing species. Most are quite demanding though, so they can't be recommended as fish for the beginner, but the halfbeaks at least would make good subjects for an aquarist with a year or two of experience and an interest in breeding some interesting fish.
Latin name: Dermogenys spp.; while most imports are tagged as Dermogenys pusilla, since that fish comes from Indonesia, imports from Thailand are more likely to be Dermogenys pusilla siamensis. Some other halfbeaks, including Dermogenys pusilla sumatrana and Dermogenys montanus, may be sold under the Dermogenys pusilla name as well.
Size: Typically 6 to 7 cm in length, with females being larger and more robust.
Water requirements: Hard, alkaline water with a small amount of salt added (SG 1.002-1.005). Oxygen levels must be high, and sudden changes in water parameters avoided.
Food: Primarily small flies, mosquito larvae, bloodworms, and other small invertebrates. Flake foods may be accepted, but do not rely on it.
Social behaviour: Males are quarrelsome among themselves and it is best to keep only a single male per tank. Otherwise a peaceful fish that should be kept in groups and away from aggressive species.
Breeding: Livebearer, but not easy to breed.
Latin name: Nomorhamphus liemi liemi is the most frequently seen but a subspecies, Nomorhamphus liemi snijdersi is sometimes imported too. Quite probably other species of Nomorhamphus turn up occasionally as well.
Size: Females up to 10 cm in length, males considerably smaller.
Water requirements: Not picky, prefers neutral water conditions but will adapt to slightly acidic or alkaline conditions if necessary. Can be kept in slightly brackish water (SG up to 1.003).
Food: Prefers small live and frozen foods, but generally takes flake foods quite willingly.
Social behaviour: While males do fight with one another, they rarely do any harm, and in a large tank it is possible to keep several males together provided there is plenty of space and lots of cover.
Breeding: Livebearer, but not easy to breed.
Latin name: Xenentodon cancila, other species exist but are rarely, if even, imported.
Size: Up to 30 cm.
Water requirements: Neutral water conditions best.
Food: Live foods at first, can be trained to accept frozen and dead foods.
Breeding: Egg-layer, this species is only rarely bred in captivity and the fry are considered to be difficult to raise.
Latin name: Oryzias spp.
Size: 1.5 to 4 cm, depending on the species.
Water requirements: Neutral to slightly alkaline water conditions preferred, but this fish is adaptable provided extremes are avoided. Some species require tropical conditions, others do best in an unheated aquarium.
Food: Flake, as well as frozen and small live foods.
Social behaviour: Peaceful, schooling fish.
Breeding: Egg-layer, with the fry being relatively easy to raise.