Red-line Halfbeak "Sijuk"

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The Red-Line Halfbeak “Sijuk” (Hemirhamphodon phaiosoma) is a rare freshwater halfbeak from Indonesia. It has a slender body, a long lower jaw, and a vivid red line that becomes especially noticeable once the fish settles into a dark, planted aquarium.

Unlike many commonly sold halfbeaks, this is a true soft-water species. It is best suited to experienced aquarists who can provide a mature blackwater-style aquarium, gentle tankmates, and plenty of room at the surface.

About This Fish

The “Sijuk” name refers to the locality associated with this form. These fish come from the island of Belitung in Indonesia, where they inhabit quiet, forested waterways.

Red-Line Halfbeaks spend nearly all their time close to the surface. Their unusual shape, bright markings, and alert hunting behavior make them unlike almost anything else in a freshwater aquarium.

They can be nervous when first introduced but usually become more confident in a quiet tank with floating plants and plenty of cover.

Aquarium Care

This species needs very soft, acidic water and should only be added to a mature, stable aquarium. It is not a good choice for hard water or alkaline community tanks.

Keep the current gentle and maintain good oxygen levels without creating rough surface movement. These halfbeaks are sensitive to sudden changes, so careful acclimation is important.

A tight-fitting lid is absolutely necessary. Halfbeaks are excellent jumpers, especially when startled. Cover any gaps around filters, airline tubing, and cables.

Tank Setup

Surface area is more important than depth. A long aquarium gives these fish room to swim without damaging their delicate lower jaws against the glass.

Use driftwood, leaf litter, subdued lighting, and plenty of floating plants. Red root floaters, Salvinia, and other plants with hanging roots provide excellent surface cover. Leave some open water between the plants for feeding and swimming.

Avoid sharp decorations near the surface. Position the aquarium in a quiet area where the fish will not be startled by constant movement.

A 20-gallon long aquarium can house a small group, although 30 gallons or larger is preferred.

Diet

Red-Line Halfbeaks are surface-feeding micro predators. They do best on small live and frozen foods such as fruit flies, mosquito larvae, baby brine shrimp, daphnia, cyclops, and small bloodworms.

Food should float or remain near the surface long enough for the fish to find it. Some individuals may learn to accept small floating pellets, but dry food should not be their only diet.

A varied diet will help maintain good condition and bring out their red coloration.

Tankmates

Choose small, peaceful tankmates that prefer the same soft, acidic water. Good options may include small rasboras, pencilfish, peaceful kuhli loaches, and other calm blackwater species.

Avoid fast surface feeders, aggressive fish, fin nippers, and anything large enough to treat the halfbeaks as prey. Busy tankmates can prevent them from feeding properly.

Males may display or chase one another. Keep a group in a roomy aquarium with floating cover, and watch for any fish being pushed away from food or confined to a corner.

Small shrimp and shrimplets may be eaten. Larger shrimp may be left alone, but they should not be considered completely safe.

Breeding Notes

Red-Line Halfbeaks are livebearers. Females give birth to fully formed fry rather than laying eggs.

Breeding is possible, but it is not considered easy. The adults must be kept in excellent condition with soft, acidic water and a steady supply of small live foods.

Dense floating plants give newborn fry a place to hide. Fry can be started on newly hatched baby brine shrimp, microworms, and other tiny live foods. Separate them if the adults or tankmates begin hunting them.

Recommended Water Parameters

Temperature: 73° to 81° F (optimal 75° to 79° F)
pH: 4.5 to 7.0 (optimal 5.5 to 6.5)
KH: 0 to 2 dKH (optimal 0 to 1 dKH)
GH: 0 to 4 dGH (optimal 0 to 2 dGH)
Minimum tank size: 20-gallon long for a small group, with 30 gallons or larger preferred
Adult size: Approximately 2 to 2.5 inches
Typical purchase size: Approximately 1.5 to 2 inches
Origin: Sijuk, Belitung, Indonesia

What We Like About This Fish

• Rare and unusual Indonesian halfbeak
• Beautiful red line along the body
• Spends most of its time near the surface
• Fascinating surface-hunting behavior
• Excellent choice for a specialty blackwater aquarium
• Safe with live plants
• Gives birth to live young

Important Notes

This is a specialized soft-water fish and is not recommended for beginners or newly established aquariums. It requires very soft, acidic water and may not adjust well to hard or alkaline conditions.

A tight lid is essential because this species can jump through very small openings. Its extended lower jaw is delicate, so provide plenty of surface swimming space and avoid anything that may cause the fish to panic.

These halfbeaks may arrive with subdued coloration. Their red markings usually become stronger after they settle in and begin feeding well. Color, size, and markings will vary between individuals.