Ikan Jenjulung: Halfbeak Fish Care for Malaysia's Native Surface Swimmers

The halfbeak fish (ikan jenjulung) is a slim, surface-hugging livebearer with a long lower jaw, and it's a native of Malaysian streams, ditches and paddy-field channels. In short: keep a group in a 2 kaki tank or larger with a tight lid, give them open water at the top, feed floating foods and small live insects, and avoid sharp décor near the glass, because a frightened halfbeak bumping into hard surfaces can break its beak. They are hardy at our room temperature of 26–31°C and breed readily. Some Malaysians also call it ikan julung-julung.

What Is a Halfbeak Fish?

Halfbeaks are small fish whose lower jaw is much longer than the upper jaw, giving a "half-beak" look. The species most often seen in Malaysian shops belong to the genus Dermogenys, including the wrestling halfbeak (Dermogenys pusilla and close relatives). Males use their jaws in sparring contests, hence the name.

They are livebearers: females give birth to live young instead of laying eggs, like guppies and mollies. Adults are usually around 5–7 cm, with females larger than males.

Native, so keep it responsible

Halfbeaks occur naturally across Peninsular Malaysia and Borneo. That makes them a great choice for a local biotope tank, but:

• Prefer captive-bred fish from sellers, rather than catching from the wild.
• Never release aquarium fish, even native ones, back into rivers or drains. Tank-raised fish can carry diseases into wild populations.

Halfbeak Aquarium Care Table

Factor	What halfbeaks need
Temperature	24–30°C; normal Malaysian room temperature is fine
Minimum tank	2 kaki (60 × 30 cm, about 55–65 L) for a small group; longer is better than taller
Lid	Essential; they are strong jumpers
Water	Clean, gentle flow; tolerates slightly hard water and a pinch of salt
Diet	Floating foods, small live insects, mosquito larvae, fruit flies, flakes
Temperament	Peaceful to other fish; males spar with each other
Group	1 male to 2–3 females, or one male only in small tanks
Beginner-friendly?	Yes, for keepers who can feed surface foods

Setting Up a Halfbeak Aquarium

Halfbeaks live in the top few centimetres of the water. Plan the tank around that.

• Length and surface area matter most. A long, shallow tank beats a tall one. See our tank size guide in kaki and litres.
• Lid with no gaps. They jump when startled, especially at night when lights switch on.
• Floating plants such as salvinia, frogbit or water lettuce give cover and calm the fish. Leave some open water for feeding.
• Soft edges. Halfbeaks dart forward when frightened. Avoid sharp rocks or wood right at the surface level. Keeping the tank in a quiet spot and switching the room light on before the tank light reduces panic.
• Gentle filter flow. A sponge filter or hang-on filter with the outflow spread across the surface works well.
• Tap water: always treat with anti klorin. Malaysian tap water is chlorinated; see the anti klorin guide.

Soft water and salt

Much of Malaysian tap water is soft with low KH, which halfbeaks tolerate, but many keepers report better health with stable, slightly harder water. Some add a small amount of garam ikan (aquarium salt), as halfbeaks naturally cope with slightly brackish water near coasts. Don't add salt if you keep salt-sensitive tankmates or plants, and test your water rather than guessing.

What Do Halfbeaks Eat?

This is the part that trips beginners up. Halfbeaks have mouths shaped for grabbing food at the surface, so sinking pellets are often ignored.

Good foods:

• Floating flakes and micro pellets for tropical fish
• Mosquito larvae (jentik-jentik), which they hunt eagerly; collect only from clean water you control, or buy cultured live food
• Fruit flies and small crickets dropped on the surface
• Frozen bloodworm (cacing darah) and artemia, thawed so they float briefly
• Daphnia or moina

Feed small amounts two or three times a day, because halfbeaks are slim and don't store much energy. A well-fed female has a gently rounded belly.

Tankmates

Halfbeaks pair well with peaceful fish that stay in the middle and bottom:

• Rasboras, including native harlequin and chili rasboras
• Small loaches and corydoras
• Small gouramis and wild-type bettas in larger, well-planted tanks

Avoid fish that compete at the surface aggressively, fin nippers, and anything big enough to swallow fry.

Breeding Halfbeaks

Halfbeaks breed readily in a healthy tank.

• Gestation is roughly 3–8 weeks depending on temperature and species.
• Fry are born large (about 1 cm) and can eat crushed flakes, baby brine shrimp and micro foods right away.
• Adults may eat fry, so give dense floating plants or move a heavily pregnant female to a separate tank or breeding box.
• Stillbirths are common if the female is underfed. Feed pregnant females well, with live and frozen foods.
• Males have a modified anal fin (an andropodium) used in mating, which helps you tell the sexes apart along with their smaller size and brighter colours.

Beak Injuries and Other Problems

Problem	Cause	What to do
Broken or bent beak	Panic swimming into glass or décor	Keep the tank calm, lights on gradually, soft décor; a broken beak doesn't regrow fully but many fish adapt
Thin, hollow belly	Not getting enough surface food	Feed floating and live foods more often
Jumping out	No lid or gaps in the lid	Cover every gap
Males fighting constantly	Too many males in a small tank	Keep one male, or give a larger tank with plants
Stillborn fry	Poor diet, stress	Better diet, quiet tank

Most problems come from stress and diet, not disease. For general sickness signs, see our kenapa ikan mati guide.

Buying Halfbeaks on FishyHub

Browse halfbeak fish listings from Malaysian sellers. Check:

• The species name (some listings are wrestling halfbeaks, others golden or other forms)
• Whether you're buying males, females or a mixed group
• Whether the photo is the actual batch
• Whether the beaks look intact and straight
• Delivery or self-collect options, and each listing's live-arrival terms

Halfbeaks travel reasonably well but are jumpy; ask the seller to bag them with enough water and air.

Frequently Asked Questions

Ikan jenjulung makan apa? Ikan jenjulung suka makanan yang terapung di permukaan air, seperti flakes, jentik-jentik, lalat buah, cacing darah beku dan artemia. Pelet yang tenggelam biasanya tidak dimakan. Beri makan sedikit, dua atau tiga kali sehari.

Ikan jenjulung bertelur atau beranak? Ikan jenjulung beranak. Betina melahirkan anak ikan yang sudah boleh berenang dan makan makanan halus dengan segera. Sediakan pokok terapung supaya anak ikan tidak dimakan oleh ikan dewasa.

How big do halfbeak fish get? Most aquarium halfbeaks reach about 5–7 cm, with females a little larger than males.

Can I keep two male halfbeaks together? In a small tank, males spar constantly. In a longer, planted tank with several females, two or more males can share space, but watch for injuries.

Do halfbeaks need salt? Not necessarily. They tolerate a little aquarium salt, but clean, stable water matters more. Don't add salt if tankmates or plants are sensitive to it.

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Ready for a native surface swimmer? Browse halfbeak fish, floating fish food and live fish food from sellers across Malaysia on FishyHub.