By Neale Monks

Halfbeaks are slender, streamlined fish closely related to the needlefishes (family Belonidae) and the flying fishes (family Exocoetidae). Although they lack the big fins of flying fish, halfbeaks are all expert jumpers, and must only ever be kept in a covered aquarium. Like needlefish, they have specialized jaws, but with Halfbeaks only the lower jaw is lengthened. This is what gives them their common name.

Around a hundred species of halfbeak are known, and while the larger species are good to eat, they are more important as prey for big game species like marlin, dolphinfish, and tuna. Halfbeaks are omnivores and eat plankton, smaller fish, and plant material, particularly small fragments of algae and seagrasses. The majority of Halfbeaks live in the sea, but there are a significant number that live in fresh water, and some of these are quite commonly traded as aquarium fish. 

Freshwater Halfbeaks from two genera, Dermogenys and Nomorhamphus are widely traded and usually easy to obtain. These normally adapt quickly to aquarium life and pose few problems for the aquarist used to keeping the larger livebearers. Dermogenys species are typically called “Wrestling Halfbeaks” by retailers, whereas the Nomorhamphus species are normally sold as “Celebes Halfbeaks”. Both of these common names really apply only to specific fish, Dermogenys pusilla and Nomorhamphus liemi, but in practice a variety of species are sold under these names, making identifying your halfbeaks more difficult that you would imagine. 

Halfbeaks from two other genera are occasionally traded, Hemirhamphodon and Zenarchopterus. These have special needs and are best kept in a single-species aquarium.

Wrestling Halfbeaks

At least three different species are sold under the "Wrestling Halfbeak" name. Identifying them to species level is very difficult, but fortunately for the aquarist these are adaptable fish and will accept a broad range of water chemistry parameters, from slightly soft and acidic through to low-end brackish. All three species will do well between pH 6.5 and 7.5 and in soft to moderately hard water. They can also be adapted to slightly brackish water (SG around 1.005). These are generally easy to keep fish, the main problem being the aggressiveness of the males, and in small aquaria (under 30 gallons) males should be kept one to a tank. Beyond that, these are the ideal oddball livebearers to keep with guppies or mollies, though they also mix in well with tetras, Corydoras catfish, and small barbs. 

Celebes Halfbeaks 

Several species of Nomorhamphus are sold, and identifying them can be difficult. Most do best in acidic to neutral (pH 6-7), soft to moderately hard water. While they will live perfectly well in hard, even slightly brackish, alkaline water, breeding is more successful when they are kept in soft, acidic water. The exception to this is Nomorhamphus ebrardtii, which prefers hard, alkaline water. In terms of general care, these are somewhat finicky fish. They do not tolerate sudden changes in pH or hardness at all well, and this probably explains the mysterious and sudden deaths of these fish that some aquarists have encountered. On the other hand, these are colorful and lively fishes well worth keeping.

Nomorhamphus brembachi Vogt, 1978. A small species up to 4 cm (1.5 inches) only found on the Indonesian island of Sulawesi. This is a delightful species with a silvery-green body, a straight beak, and red, black and blue markings on the fins. Males are especially brightly coloured. Prefers soft to moderately hard, slightly acidic to neutral water. Easily confused with the very similar but larger Nomorhamphus liemi in earlier shipments of Celebes halfbeaks, this species is now being deliberately exported from Indonesia and given its small size and bright colors will likely become quite popular in the future.

Nomorhamphus ebrardtii (Popta, 1912). Another Halfbeak from the island of Sulawesi, this species is sometimes sold as the “red fin halfbeak” but is more often simply included in batches of Celebes halfbeaks. Unlike Nomorhamphus liemi, this species has a straight beak and the fins are edged with thick bands of orange. It is quite a large species, with females around 11 cm (4.5 inches) in length and males around 9 cm (3.5 inches). Nomorhamphus ebrardtii is found in coastal waters rather than rainforest streams, and needs moderately hard, neutral to slightly alkaline water. It will also tolerate slightly brackish water (SG up to 1.005). 

Nomorhamphus hageni Vogt, 1978. A rare stowaway species from Sulawesi, this species has a greenish-grey body that can sometimes take on a spectacular coppery tone. The anal and dorsal fins are orange, while the tail fin has a vertical orange band about halfway out from its base. Males have short, straight beaks. A fairly large species, females are about 10 cm (4 inches) in length, and males a bit smaller. Because it is not widely kept, its preferred water conditions are unknown, but are likely to be similar to those of Nomorhamphus brembachi. 

Nomorhamphus liemi Vogt, 1978. Restricted to the Indonesian island of Sulawesi (Celebes), this is the standard issue Celebes halfbeak and one of the most widely traded halfbeaks. Males can be immediately recognized by their goatee-like beak, which curls downwards under the mouth. Both sexes are marked with red, blue, and black patches on the fins and face, though the male is the more brightly coloured of the two. Females get to about 10 cm (4 inches) in length, and the males around 6 cm (2.5 inches). This species prefers soft and acidic water conditions. 

Nomorhamphus ravnaki Brembach, 1991. Not deliberately imported, but this Sulawesian species seems to be a regular stowaway in batches of Nomorhamphus liemi. The most immediate difference between the two species is that Nomorhamphus ravnaki has red rather than red, black, and blue patches on the dorsal and tail fins. The anal fin is yellow edged with black. Males and more brightly colored than the females, and have a straight beak marked with red. Otherwise it is very similar to Nomorhamphus liemi in terms of size and maintenance. 

Rarely-Traded Halfbeaks

Hemirhamphodon pogonognathus (Bleeker, 1853). Widely distributed across Southeast Asia but nonetheless relatively rare in the hobby. The bearded halfbeak is a very beautiful but challenging species. Both sexes have pinkish-blue bodies and fins edged with electric blue. Males have a long “beard” dangling from the tip of the lower jaw and the anal fin is bent about halfway down and forms a structure that points backwards a bit like the sword on the tail of a male swordtail. Females lack the “beard”, and the anal fin is not bent, and has a simple approximately triangular shape. Males are about 9 cm (3.5 inches) in length; females are smaller. In the wild, these fish live alongside Chocolate Gouramis, rasboras, and other soft water fish. They need very soft (ideally below 5 degrees GH), fairly acidic (pH 5-6) water filtered through peat to last any length of time. In harder, more alkaline water they tend to be sensitive to bacterial infections and parasites. Floating plants, such as duckweed or Ceratopteris will help these fish settle in and inhibit their tendency to jump. 

Hemirhamphodon kapuasensis Collette, 1991. Similar to the bearded halfbeak in shape, but the males lack the beard. Distinguished by having a very attractive pattern of irregular red and blue stripes along the flanks. Hemirhamphodon kapuasensis is similar to Hemirhamphodon pogonognathus in requirements, but is much smaller, males only getting to around 5 cm (2 inches) in length. 

Zenarchopterus buffonis (Valenciennes, 1847). These fish are common in shallow seas and estuaries along the coastlines between India and Australia. It is sometimes sold as a freshwater fish, though over the long term should be kept in brackish or marine conditions. Easily distinguished from other Halfbeaks by its size, very long beak, and the dark band running from above the eye to the base of the tail. These fish are very nervous and need to be kept in a large, quiet aquarium, preferably on their own. A high hardness and pH (7.5+) is essential, and these fish are best maintained in a brackish water aquarium with a specific gravity of 1.010 or more.

Purchasing and Acclimating Halfbeaks 

Dermogenys and Nomorhamphus spp. Halfbeaks are quite robust little fish, though the first few days can be dicey. When you buy your fish, avoid exposing them to extremes of heat or coldness on the way home. Once you have them home, acclimate them to the water conditions in your aquarium gently. Ideally, put the halfbeaks in a large, covered bucket containing the water they came home it, and add small amounts of aquarium water every 10-15 minutes. Keep the lid on the bucket the rest of the time because these fish jump when scared! After 1-2 hours, the fish should have been adjusted to the new water chemistry conditions and can be carefully netted out and transferred to their new home.

The other Halfbeaks are significantly more delicate, and you will need to adjust them even more carefully. These fish should certainly be kept in isolation until you have them feeding properly, and it is questionable whether any of them are really suitable for community tanks. 

Water Chemistry and Filtration 

Halfbeaks are generally fairly adaptable, with the exception of Hemirhamphodon and Zenarchopterus spp. However, sudden changes in water chemistry can often be lethal and must be avoided. For breeding purposes, providing water chemistry values closer to the optimal range for the species in question is often helpful. While halfbeaks will breed outside their preferred range, they do less frequently. Water quality is also very important. Though Dermogenys spp. Halfbeaks are about as tough as any community tank tetra or barb, all Halfbeaks benefit from being kept in tanks with good filtration, frequent water changes, and lots of oxygen. 

Aquarium 

Halfbeaks have evolved to utilize open water. They are completely indifferent to things like substrate and rocks, though floating plants and leaves are appreciated. Females and subdominant makes will hide among tall plants when chased by dominant males, and the fry invariably hide in floating plants given the option. For the latter purpose, hornwort and Cabomba are especially useful. Water depth is relatively unimportant.

 Behaviour

Possibly the most entertaining thing about halfbeaks is their social behaviour. Apart from Zenarchopterus spp, they are not really schooling fish except when very young. Males are invariably territorial, and Dermogenys are so fierce that in parts of Asia they are used as “fighting fish” for the purposes of gambling in much the same way as Siamese fighting fish. It is from this that they are called “Wrestling Halfbeaks”. Nomorhamphus and Hemirhamphodon are not so violent and males will coexist in large tanks with plenty of hiding places.

Female Nomorhamphus are sometimes a little snappy, especially towards males that annoy them, but this rarely causes any problems in the long term. By contrast, female Dermogenys and Hemirhamphodon are fairly placid and tolerant. Neither male nor female Zenarchopterus show any aggression towards one another, and in fact seem to be perfectly normal schooling fishes that must be kept in groups.

Finally note that different species of halfbeak can be aggressive towards one another, and because of the differences in size and temperament, males of different species should not be mixed. A large, aggressive species could easily damage, even kill, a smaller, more passive one.

 Food

As mentioned earlier, halfbeaks are omnivores. In the wild, freshwater species feed on a variety of things, from insect larvae to pollen. In captivity, an algae-based flake food (such as that formulated for mollies and guppies) is the ideal staple, supplemented with frozen bloodworms a few times a week. Among the live foods they enjoy are mosquito larvae, Daphnia, and fruit flies, all of which are excellent for conditioning females for breeding. Useful treats include krill, lobster eggs, and small pieces of prawn and fish. 

Breeding 

With the exception of Zenarchopterus spp., all the freshwater halfbeaks described here are livebearers. The exact details vary markedly from species to species, with some species being ovoviviparous (like Guppies) and other viviparous (like goodeids). Some species even practice oophagy, with embryonic Nomorhamphus ebrardtii eating some of their siblings in the ovary with them! 

Male halfbeaks are equipped with a modified anal fin called an andropodium that delivers sperm into the female. Some halfbeak species can store sperm long enough to fertilize three or more broods, but not all of them. The males flutter their fins in front of the female and then spend much of the time following her about, staying behind and below her. Mating itself is brief. After being fertilized, the female will often drive the male away, or at the very least show her irritation if he approaches her again. 

Broadly speaking, Halfbeaks produce smaller broods than the common Central American livebearers, and while raising the fry isn’t especially difficult, ensuring that the female carries them to term can be. For best results, the female should not be moved at all after fertilization, and she should be kept warm and provided with a high-quality diet. Water chemistry and quality should be monitored carefully. The gestation period varies from species to species but is typically 4-6 weeks. 

Around 10-20 fry are produced per batch. Nomorhamphus fry are quite large -- around 12 mm (0.5 inch) in length -- and will take powdered flake and live foods such as small Daphnia at once. Dermogenys fry are a bit smaller, so newly hatched brine shrimp or small pond foods should be used instead. Halfbeak fry grow rapidly and are easy to care for. 

Final Thoughts 

Halfbeaks are lovely fish; they are colorful, lively, and full of personality. In many ways they are the Asian equivalents of the Central American Poecilidae and occupy a similar ecological niche in the wild. For the aquarist after a sociable, relatively easy to breed oddball, they make an excellent choice.