Some fish species, such as the catfish (order Siluriformes) show remarkable adaptations to their environment. For example, the labyrinth catfish family (Clariidae) is named after an organ arising from the species’ gills, which allows them to breathe atmospheric oxygen.

Borneo’s walking catfish

This peculiar family includes the forest walking catfishes, as some species are capable of travelling short distances on land. Able to survive out of water for extended periods, the walking catfishes are caught for food relatively easily and are subject to subsistence fishers and commercial farming operations.

Catfishes come in a range of colours and shapes. Species of the family Parakysidae are well camouflaged, hiding in small forest streams, and have wrinkly skin, branched barbells and a forked tail.

The family Bagridae are some of the largest catfishes in the world. They have conspicuous dorsal and pectoral spines, a distinct adipose fin (a small fin located behind the dorsal fin) and often deeply forked caudal (tail) fins.

Less conspicuous, the glass catfishes (family Schilbeidae), also known as ghost catfishes or phantom catfishes, are almost transparent, revealing their skeleton and internal organs.

Needs and lifestyles of Borneo’s freshwater fishes

Some freshwater fish have adapted to very specific habitats. For example, Waandersii's hard-lipped barb (Osteochilus hasseltii) live in clear, freshwater, tropical streams, with a preference for fast-flowing streams and rivers, where gravelly or stony substrate is available. When water levels rise, it moves into the flooded areas adjacent to rivers.

The spotted eel-loach (Pangio shelfordii), also known as the spotted coolie loach or Borneo loach, keeps to muddy, slow-flowing streams and pools in freshwater swamp forests. This orange fish, with a pattern of dark splashes, is difficult to see as it lies amongst the leaf litter and plant detritus.

Borneo also has its own bony-tongue fish (Scleropages formosus), also referred to as the Asian Arowana, which is confined to slow-flowing rivers and lakes.

Prized for the belief in its positive fengshui, large specimens can fetch up to US$20,000 and wild populations are severely threatened by habitat degradation and the aquarium trade.