Halfbeaks

First catch your halfbeaks...!

Probably the most difficult thing about halfbeaks is finding them, so when you do find some, it’s best to snap them up right away. For anyone who’d like to try out ‘rare’ livebearers, halfbeaks are relatively easy to keep and mix well with other community fish. There are some things to remember though:

Halfbeaks are intolerant of heat stress
Halfbeaks are intolerant of low oxygen concentrations (e.g., inside a bag)
Halfbeaks react badly to sudden changes in water chemistry

In other words, don't buy them on the hottest day of the year, and try and get them from a store close to home so that you can get them into your aquarium quickly as possible. Once you have them back home, adapt them to your home aquarium slowly. I'd recommend piercing the bag with a needle and then letting water diffuse between the bag and the tank over at least an hour.

Distinguishing Nomorhamphus, Dermogenys, and Hemirhamphodon

The next problem is identifying your halfbeaks. Broadly speaking, retailers normally manage to separate Nomorhamphus from Dermogenys, but within these two genera, little effort seems to be made to correctly identify individual species. A batch of Celebes halfbeaks, for example, though ostensibly Nomorhamphus liemi, can, and often does, include specimens from other species, most often Nomorhamphus ebrardtii. There are two other genera of halfbeak that have been traded in the past, Hemirhamphodon and Zenarchopterus.

Separating out the four genera is in fact rather easy.

At any given size, Nomorhamphus species are by far the most sturdily built and have a deep, barrel-chested body and only a short, stubby beak.
Dermogenys, on the other hand, is comparatively slender, and when viewed from above, has distinctive “flanges” on either side of the mouth.
Hemirhamphodon is easily the most delicate of the four, with a long, narrow body and a very long beak. In fact the beak is around one-third the body length.
Compared with the others, Zenarchopterus species are much bigger and not sexually dimorphic; in appearance they look more like needlefish than halfbeaks

Behaviour can be a useful clue as well. Nomorhamphus will happily swim at the middle depths of the aquarium, and may even approach the substrate if they think some food might be found there. Dermogenys, and especially Hemirhamphodon, stay much closer to the surface of the water. Dermogenys may dive a few centimetres beneath the surface to snap up prey, but Hemirhamphodon hardly do so at all.

Another behavioural clue to Hemirhamphodon is the positioning of its tail fin; while species of Nomorhamphus and Dermogenys both ‘tread water’ with the tail fin open, Hemirhamphodon tends to have the tail fin closed and instead seem to paddle into the ambient water current using their large pectoral fins.

Zenarchopterus have a very distinctive personality compared to the other halfbeaks, being nervous, completely non-aggressive and highly sociable schooling fish.

Commonly traded halfbeak species

Identifying species of Nomorhamphus and Dermogenys is difficult. There is little in the aquarium literature that documents all of the known species (the exception being perhaps the Aqualog book); instead, most retailers assume that the halfbeaks they are trading are either Celebes halfbeaks, Nomorhamphus liemi, or wrestling halfbeaks, Dermogenys pusilla. In fact, there are multiple species of both genera in the trade. The following is a quick key to the most frequently traded species.

Key to commonly traded Dermogenys

1. Silvery green, pelvic fins closer to pectoral fins than anal fin: D. pusilla
2. Bright silver with a pink or greenish tint: D. siamensis
3. Silvery brown, pelvic fins closer to anal fin than pectoral fins: D. sumatrana

Key to commonly traded Hemirhamphodon

1. Pinkish-blue body, tail and anal fin edged with electric blue: H. pogonognathus
2. Small, with broken, red and blue stripes on flanks: H. kapuasensis

Key to commonly traded Nomorhamphus

1. Straight beak, solid orange or red fins: N. ebrardtii
2. Curly beak, fins marked with red, black, and blue: N. liemi
3. Straight beak, dorsal and anal fin orange, tail orange only towards its base: N. hageni
4. Straight beak, dorsal and tail fins red, pelvic and anal fins yellow: N. ravnaki
5. Straight beak, slightly marbled, grey body and grey fins: N. towoetii

Note that females Nomorhamphus have shorter beaks than the males and are often, but not always, less brightly coloured.

Key to commonly traded Zenarchopterus

1. Large, very long beak, thick dark band along the flanks: Z. buffonis

Learning more

There isn't much about these fish on the Internet compared with catfish or puffers, but there are some good pages worth reading. These include:

Halfbeaks, Brackish Aquarium FAQ
Halfbeaks, at the Minnesota Aquarium Society
Hemirhamphidae, at the Ferrarese Aquarium & Herpetology Association (in Italian, but a good gallery)

As far as books go, Baensch’s Aquarium Atlases cover the basics. Dermogenys pusilla and Nomorhamphus liemi are in volume 1; D. sumatrana and Hemirhamphodon pogonognathus are in volume 2; and N. ebrardtii are in volume 3. There are more species in All Livebearers and Halfbeaks from Aqualog. John Dawes’s book Livebearing Fishes: A Guide To Their Aquarium Care, Biology and Classification contains a fair amount on halfbeaks though its main focus is poecilid livebearers. Likewise, Peter Scott’s Livebaring Fishes only has a small amount on halfbeaks, though it is a useful little book otherwise.

Are halfbeaks suitable for beginners?

Halfbeaks are small, lively, and inexpensive, and are consequently considered attractive fish by newcomers to the fishkeeping hobby. They can in fact make very good fish for beginners, as they are not especially demanding as far as food and water chemistry go. In fact, once settled in they are adaptable and quite easy to keep.

However, they can be delicate for the first few days after being placed in a new aquarium. Some species prefer live foods, and all will more readily take frozen foods (such as bloodworms) over flake or pellets. No halfbeak appreciates a sudden change in water chemistry, and they are thus best suited to aquaria that have been running for a few weeks and acquired some degree of stability.

Water conditions and filtration

Generally speaking, halfbeaks are adaptable and do not have specific water chemistry requirements. Breeding Nomorhamphus liemi is said to be easier in soft and acidic water, and my fish have certainly bred well in water with a pH 6.5-7.0. Nomorhamphus ebrardtii possibly prefers harder, more alkaline conditions. Dermogenys spp. are very adaptable, and will tolerate anything from soft and acidic through to slightly brackish. Contrary to popular belief, Dermogenys spp. do not need brackish water, though many species will certainly tolerate it and Fishbase at least reports that Dermogenys pusilla is occasionally found in the sea.

As far as water quality goes, halfbeaks appreciate good clean water as much as any other fish, but they are not put out by high nitrate levels. Indeed, my experience is that performing very large water changes can cause problems if the pH and hardness levels suddenly change. Regular, but small, water changes seem to work best.

Both Normorhamphus and Dermogenys appreciate a good strong water current, but oddly Hemirhamphodon seems not to, preferring to rest in shady corners with a more sluggish flow of water.

Food

Freshwater halfbeaks are usually said to be carnivorous, feeding primarily on insects such as mosqitoes and mosquito larvae. Fishbase also reports them taking worms and crustaceans. In captivity they will sometimes take algae-based flake food, so like their marine relatives, freshwater halfbeaks may well be omnivores rather than strict carnivores.

My first batch of halfbeaks showed no interest in flake foods and only ate things like shrimp eggs and bloodworms. The second batch ate flake foods as well, and this encouraged the other halfbeaks to eat flake foods as well, so to some extent they seem to eat whatever other members of the school are eating. Foods my halfbeaks enjoy include:

Bloodworms (live or frozen)
Daphnia (live)
Mysis and krill (frozen)
TetraMin flake
Spirulina flake
Shrimp eggs (scraped from shrimp sold at the supermarket)
Lobster eggs (frozen, sold for feeding marine invertebrates)
Small pieces of frozen prawn, squid, etc.
Insects such as flies and live mosquito larvae

They have little to no interest in frozen Daphnia or Artemia, and only certain types of dried food are consumed, notably Hikari Micro Pellets, which are eaten even by the otherwise rather fussy Hemirhamphodon.

Wild fish are said to be partially herbivorous, with fish collector and writer Frank Schaefer having mentioned that Dermogenys feed on pollen grains in the wild. Sometimes my halfbeaks will consume Spirulina-based flake foods, though not with much enthusiasm.

One tablet of frozen mysids had a small fish in it, and this was immediately eaten by the largest halfbeak; it is therefore quite possible that large halfbeaks will also eat livebearer fry and other small fishes. That said, my adult Nomorhamphus, despite being anything up to 10 cm long, have shown no interest in fish as small as cardinal tetras.

Social behaviour

All halfbeaks are aggressive towards one another to some degree, and they will spend much of the time chasing one another or engaging in threat displays and fights. Males attempt to monopolise access to the females, and will drive subdominant individuals into hiding. These vanquished males will often swim into deeper water or hide among plants. Females are less aggressive, and while they will chase other individuals or threaten them, they don’t seem to fight much, if at all.

Aggression will certainly cross the species boundary within the confines of the aquarium. Where there are multiple Nomorhamphus species in the same aquarium, males of all species will threaten and attack one other indiscriminately. Some Nomorhamphus species are more aggressive than others, N. ebrardtii especially seeming to be very pugnacious and able to dominate even a 180-litre aquarium.

Fighting may occur between species from different genera, too. Species of Hemirhamphodon will threaten species of Dermogenys, for example. However, these intra-generic fights seem to be brief and usually harmless. There may be a pecking order of some type between the genera, so while the three genera of freshwater halfbeak might be mixed, bear in mind the size differences. Adult Nomorhamphus males in particular will bully the smaller Dermogenys.

As far as other species of fish go, halfbeaks are easy to accomodate. My specimens have coexisted amicably with tetras, glassfish, hatchetfish, small pufferfish, and dwarf cichlids.

Lifespan and fertility

Although they are not particularly disease-prone, halfbeaks do not seem to be very long lived fish. The smaller Dermogenys species may well be annual fish, and only exceptionally last for more than 18-24 months after purchase, at which point they are likely a good six months old already. The bigger Nomorhamphus species may live a little longer, but 2-3 years seems to be the upper end of their lifespan range.

One peculiar but widely reported aspect of their aging process is a distinct reduction in fertility as they age. Whether this is related to the males, females, or both sexes is unknown. But in any event, if you want to breed these fish, it helps to start with relatively young livestock. Successive broods seem to get smaller and less frequent, and older females appear, in my experience, to have a greater risk of miscarriages and other (apparently lethal) problems with the gestation process where the embryos fail to be delivered properly.

On the next page, Breeding

Nomorphamphus liemi liemi bagged and ready for transport