Halfbeak basics
Halfbeaks are small, slender surface-dwelling fish named for their elongated lower jaw. The best-known aquarium species is the wrestling halfbeak (Dermogenys pusilla), which occurs across parts of South and Southeast Asia in slow or still waters with plenty of surface vegetation. Halfbeaks are livebearers, which means females give birth to free-swimming young instead of laying eggs.
They are interesting rather than flashy: they hover right under the surface, and males of some species lock jaws in harmless-looking sparring matches. They can be delicate when first imported and are nervous fish, so a calm, well-planted tank helps.
Different halfbeak species
The trade often sells several species under the same common name. The most commonly mentioned are:
- Wrestling halfbeak (Dermogenys pusilla). Probably the most widely available.
- Dermogenys siamensis and Dermogenys sumatrana. Sometimes sold under the same “wrestling” or “dwarf” label when available.
- Celebes halfbeak (Nomorhamphus species). Often sold under the Celebes name, and tends to be a bit larger and more colorful than wrestling halfbeaks.
- Borneo redline halfbeak. A forest species that is often said to prefer softer, more acidic water than the wrestling halfbeak.
Needs differ between species, so identify what you have before setting water parameters. If a seller cannot say which species it is, treat that as a warning sign.
Platinum halfbeaks
Some specialty sellers offer a platinum or pale color form of the wrestling halfbeak. Availability varies and the fish tend to be sold in small numbers by independent breeders and online retailers rather than in every shop. Care is generally treated as the same as for standard wrestling halfbeaks. Ask the seller how the fish were kept and what they were fed before purchasing.
Tank size and layout
A small group can be kept in a tank of roughly 15 to 20 gallons, with a long footprint preferred over a tall tank. For these fish, surface area matters more than depth, because they spend nearly all their time just below the surface.
- Tight-fitting lid. Halfbeaks are strong jumpers. Leave no gaps.
- Floating plants. Frogbit, duckweed or similar plants reduce startling and give cover.
- Tall plants around the edges. These reduce the chance of fish striking the glass and damaging their delicate mouths.
- Gentle flow. Keep water clean and well oxygenated without strong currents.
Decor below the surface is mostly a matter of preference.
How long to wait before adding fish
Do not add fish to a brand-new tank straight away. A new aquarium needs time for beneficial bacteria to establish so that ammonia and nitrite from fish waste are processed. For most tanks this takes several weeks. Rather than relying on a fixed number of days, test the water: the tank is generally considered ready when ammonia and nitrite read zero and nitrate is present while the cycle is running with an ammonia source. Add halfbeaks gradually, because they are sensitive to deteriorating water quality.
Water parameters
For wrestling halfbeaks, commonly given ranges are:
- Temperature: about 75 to 82°F (24 to 28°C). Some sources give 72 to 82°F.
- pH: about 6.5 to 8.0.
- Hardness: moderate to hard, often cited around 10 to 20 dGH.
Hard, fairly alkaline water usually suits wrestling halfbeaks well. Some keepers add a small amount of salt (low brackish levels) to the water, particularly in tanks without live plants, but it is not essential if the water is hard and alkaline. Do frequent, smaller water changes rather than large ones, since sudden swings in temperature or chemistry can stress them.
Feeding
Halfbeaks feed almost entirely at the surface and rarely chase sinking food. Good foods include:
- Live or gut-loaded fruit flies, which are often described as ideal.
- Frozen or live brine shrimp, daphnia, mosquito larvae and bloodworm.
- Floating flakes or pellets, which some fish refuse at first but often accept over time.
Offer a protein-rich diet in small portions and remove what is not eaten.
Tank mates, including gobies
Halfbeaks do best with peaceful fish of similar size that share the same water conditions. Livebearers such as platies, small rainbowfish and some freshwater gobies are frequently suggested. Avoid larger or aggressive fish, which can make them shy and outcompete them for food. Fish that live at the surface and are fast feeders can also take food before halfbeaks reach it.
Are freshwater gobies hard to keep? It depends on the species. Some are small and fairly easy, while others need brackish water or specific diets. Check the needs of the particular goby before pairing it with halfbeaks.
Behavior, sexing and breeding
Males are smaller and have a modified anal fin used for mating, while adult males also tend to show a red patch on the dorsal fin. Keeping a group usually makes them less skittish. Males spar with each other, but serious damage is uncommon when there is enough space. Keep either one male or several males to spread out the aggression.
Breeding is possible but not always easy, as many females give birth to stillborn young. Good nutrition is often linked to that problem. Gestation depends on temperature, and broods are commonly 10 to 20 young. Adults may eat the fry, so removing the fry or using dense surface plants helps. The fry can usually take powdered foods or newly hatched brine shrimp.
Common problems
- Jumping out. Use a tight lid and floating plants.
- Injured mouths. Dense planting and a calm tank help.
- New arrivals declining. Newly imported fish can be delicate. Keep water stable and offer live food.
- Refusing dry food. Be patient and mix in live or frozen foods.
If you are also considering other unusual species for a different tank, our guide to freshwater eel tank size shows why predatory fish like eels are not suitable neighbors for small, peaceful surface dwellers.