Borneo Redline Halfbeak Care Guide - Aquarium Setup, Diet & Breeding

The Borneo Redline Halfbeak is a slender surface-dwelling fish with an elongated body and a distinctive halfbeak profile. Its lower jaw projects beyond the shorter upper jaw, while a reddish lateral line and warm red-orange markings give the species its common name. The remaining body is usually silver, olive or subtly bronze, with delicate iridescence that shows best under subdued lighting.

This species spends much of its time directly beneath the water surface, where its upturned mouth is well suited to picking insects and other small prey from the surface film. It is an alert, agile swimmer and can launch itself from the aquarium when startled, despite its generally peaceful temperament.

In nature, Borneo Redline Halfbeaks inhabit quiet or gently flowing waters shaded by overhanging vegetation. Fallen leaves, branches and dense marginal plants create a broken, dimly lit environment, and the water may be soft, acidic and heavily coloured by tannins.

They are most impressive when kept in a group, allowing natural social behaviour and courtship displays to develop. Males may spar briefly or display to females, but serious aggression is unusual when the fish have adequate space and there is plenty of cover at the surface.

Hemirhamphodon tengah is native to the island of Borneo in Southeast Asia, where it is associated with slow-moving, tannin-stained forest streams and peat-swamp habitats. Its precise distribution is linked to the freshwater systems of Malaysian Borneo, particularly areas of Sarawak and neighbouring regions.

A group should be given at least 60 litres, with a footprint of around 60 by 30 cm or larger rather than a tall, narrow aquarium. Use a secure, tightly fitting lid because these powerful surface swimmers are accomplished jumpers. Provide gentle filtration and subdued lighting, with floating plants such as Salvinia, frogbit or water lettuce creating shelter at the surface. A dark sand or fine-gravel substrate, driftwood, leaf litter and dense planting help recreate their shaded blackwater habitat, while open surface lanes should remain available for swimming and feeding. Stable, clean, soft water is more important than a strong current.

Up to about 7 cm (2.8 in) in total length. Females are generally larger and deeper-bodied than males, while males are usually more slender.

This species is primarily an insectivore that feeds at the surface. Offer a varied diet of fruit flies, mosquito larvae, daphnia, brine shrimp, small insects and other appropriately sized live or frozen foods, supplemented with quality floating micro-pellets or flakes. Foods should remain at the surface long enough for the halfbeaks to feed comfortably; occasional small live prey can help maintain their condition and encourage natural feeding behaviour.

Borneo Redline Halfbeaks can be kept with peaceful, similarly sized fish that prefer soft, slightly acidic water, including small rasboras, peaceful tetras, pencilfish, dwarf Corydoras and small freshwater gobies. They are best avoided with fin-nipping species, boisterous fish and larger predators. Do not mix them with aggressive surface-dwellers or fish likely to compete intensely for floating food, and remember that their long fins and surface position can make them vulnerable to persistent nippers.

Borneo Redline Halfbeaks are livebearers, with fertilisation taking place internally. In a mature, well-maintained aquarium, females may produce broods of relatively large, free-swimming fry after a gestation period of several weeks. Provide dense floating plants, moss or other cover so the young can avoid adults, and offer newly hatched brine shrimp, microworms and other suitably sized foods. A separate nursery tank is useful if a high survival rate is desired, as adults may eat newborn fry.

Females tend to be larger and fuller-bodied, particularly when carrying developing young. Males are smaller and slimmer, and their anal fin is modified for internal fertilisation; they may also show more pronounced colour and fin markings during display.