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
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
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.
Dermogenys pusilla Kuhl & van
Hasselt, 1823. This is the true Wrestling Halfbeak. It is widespread across
South and South East Asia, from India to the Philippines. Coloration is very
variable, but typically semi-transparent greenish-yellow to grey, with the
male having red patches on the dorsal and anal fins. Females are larger, and
they have yellowy fins, though their colors are never very strong. The
females get to be about 7 cm (3 inches) in length, while the males remain a
little smaller. Males are extremely aggressive towards one another, but the
females are more sociable, so ideally keep three or more females but only
one male in the aquarium. In terms of water chemistry, this species is very
adaptable, and can be kept in anything from soft and acidic fresh water
through to slightly brackish water with a specific gravity of around 1.005.
Dermogenys sumatrana, one of the "Wrestling Halfbeaks".
A pregnant female (top) and a male and two females (bottom).
Dermogenys siamensis Fowler,
1934. This species is limited to western South East Asia, between Thailand
and Vietnam. While it may simply be sold as the Wrestling Halfbeaks,
it is sometimes offered as the “Dwarf Halfbeak” or “Silver Halfbeak”,
references to its small size, around 4 cm (1.5 inches) and silvery color.
Males have red dorsal fins and yellow tail and anal fins. Females are less
strongly colored, with the fins being having only a slight yellow tinge and
sometimes a trace of red on the dorsal. It is otherwise similar to
Dermogenys pusilla in terms of care.
Dermogenys sumatrana (Bleeker,
1853). This species is restricted to certain parts of Indonesia,
specifically Singapore, Sumatra, and Borneo. While this species is fairly
commonly sold, it is so similar to Dermogenys pusilla in size and
coloration that the two species are rarely, if ever, distinguished.
Nonetheless, they are not impossible to tell apart, the key being the
positioning of the ventral fins. On Dermogenys pusilla, these fins
are about halfway between the pectoral fins and the anal fin, but on
Dermogenys sumatrana the pelvic fins are very close to the anal fin.
Maintenance is similar to Dermogenys pusilla, though this species is
said to be much less common in brackish water.
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 species of halfbeaks are often hard to distinguish.
From top to bottom,
N. hageni, N. ebrardtii and N.
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
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.
Hemihamphodon pogonognathus, the "Bearded Halfbeak" is common in
it's natural range, but rarely enters the pet trade.
(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.
(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
Purchasing and Acclimating Halfbeaks
N. Liemi bagged up and ready for the trip home from the local
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.
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.
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
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.
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.
Typical appearance of halfbeak fry.
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
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.
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