Identifying halfbeaks can be tricky because few aquarium books feature more than a single species (if that). Moreover, exporters seem to make no efforts at all to identify these fish, hence multiple species can get traded under the "Celebes halfbeaks" and "wrestling halfbeaks" names.

Only four genera have been traded as aquarium fish, of which only two, Dermogenys and Nomorhamphus, are common. The other two genera are Hemirhamphodon and Zenarchopterus, but these are extremely rare in the hobby.

Hemirhamphodon pogognathus is a small, freshwater species distinguished by a very slender appearance and a small, beard-like tassle under the beak. Zenarchopterus dispar is large (15 cm+), very slender, and is a brackish water fish that closely resembles a needlenose gar.

Genus-level identification

Species of Nomorhamphus seem to be the most commonly seen halfbeaks in the UK, while in the US species of Dermogenys are perhaps more widely seen. The two genera are relatively easy to tell apart. Nomorhamphus tends to be bigger and is invariably more solidly built, with a distinctive, barrel-chested appearance. Dermogenys species are slender. In terms of behaviour there are some differences, too. Nomorhamphus species halfbeaks will swim at the top and midwater levels of the aquarium, whereas Dermogenys species invariably stay close to the surface. Male Nomorhamphus halfbeaks are also not quite so aggressive as male Dermogenys.

However, the best way to tell the genera apart is to look at them from above. All Dermogenys halfbeaks have a pair of semi-transparent flanges on either side of the mouth, resulting in a scoop-like structure. This structure is not seen on Nomorhamphus.

The common species of halfbeak

By far the most common species of Nomorhamphus is Nomorhamphus liemi. Males have curly beaks and patches of red, blue, and black on their fins. Females of this species can get very big (around 10 cm), while males are smaller (6-7 cm).

The only other Nomorhamphus that seems at all widely sold is Nomorhamphus ebrardtii, known as the red-fin halfbeak. Males have stubby, straight beaks and the fins, if marked at all, are edged with red or orange. Sometimes the bodies of both males and females have a coppery hue.

Nomorhamphus ravnaki may also be seen. Males have fairly long, straight beaks, and the fins are fairly solidly marked with yellow, orange, or red. With the exception of Nomorhamphus ebrardtii, all the Nomorhamphus halfbeaks want soft to moderately hard water; uniquely, Nomorhamphus ebrardtii occurs in slightly brackish water, and doesn't do particularly well in soft, acid water conditions.

Within Dermogenys, identifying species is very difficult. There are probably three species sold, Dermogenys pusilla, Dermogenys siamensis, and Dermogenys sumatrana. Contrary to popular belief, these fish do not need brackish water.

Identifying them to species level is difficult. Male Dermogenys pusilla is brightly marked with red and yellow on the fins but females may lack these markings. Dermogenys siamensis and Dermogenys sumatrana are silvery fish without much colour at all. They are often sold as "silver halfbeaks" or "albino halfbeaks".

Further reading

Baensch's Aquarium atlases (particularly volumes 1 to 3) cover most of the species mentioned here. The Aqualog book, Brackish Water Fishes, covers Zenarchopterus in depth and explains clearly why Dermogenys halfbeaks don't need salty water. The Aqualog Livebearers book has a photo guide to all the traded species as well as many other halfbeaks less frequently seen, if at all. I've collected some information on a few of the halfbeaks on my web site, here and here.

Cheers,

Neale

This post has been edited by nmonks: Jun 6 2006, 12:02 PM

thanks for the info...so basically i have one of the three Dermogenys awesome.

lol nice guide. Now when people buy my dermogenys pusila, they won't have to ask me what kind they are.