Malayan bonytongue

Scleropages formosus

Order: Osteoglossiformes

Family: Osteoglossidae

Genus: Scleropages

Malayan bonytongues are considered an archaic (ancient group of fishes) freshwater species. They grow to 90 cm in length, and have a long body with large, elongated pectoral fins with the dorsal and anal fins located quite far back on the body. The caudal fin is much larger compared to the fin size on related bonytongues. The mouth is oblique with a very wide gape. The prominent lower jaw has one pair of barbels at the very tip. They have teeth on a number of bones in the mouth including the jaw, as well as on the tongue, hence the name “bonytongue” The scales on the body are large, cycloid with a distinctive mosaic-like pattern. Individual scales are very stout and bony, with canals which form this mosaic-like pattern. The lateral scales are arranged in horizontal rows. The mature fish has brilliant metallic gold lateral scales, gill covers, and fins, becoming darker towards the tail. The anal fin and bottom portion of the caudal fin are light brown to a dark red. Juveniles start out being metallic silver before developing into the golden colour. Colour variations are bred by hobbyists.

Conservation Status: IUCN

Distribution

They are native to Asia: southern Myanmar to the Malay Peninsula and Indonesia, eastern Thailand into the Cardamon Range.

Habitat

Tropical - Freshwater. They inhabit tannin stained (black water) streams and/or slow moving, forest covered waters flowing through swamps and peat saturated wetlands.

Diet

Malayan bonytongues are a predatory fish. Adults feed on other fishes, amphibians and small waterfowl. Juveniles primarily eat insects taken at the water/air interface.

Reproduction

Adult pairs have a lengthy courtship; it lasts from several weeks to months. During this stage, the breeding pair swims near the water surface (usually at night). The male chases the female; sometimes the pair circles each other nose-to-tail. About one to two weeks before spawning takes place, the fish swim side by side with their bodies touching. Eventually, the female releases a cluster of orange-red eggs. The male fertilizes the eggs and then scoops them into his mouth where he incubates them. The eggs are about 8 -10 mm in diameter and rich with yolk. After hatching, which occurs in about a week, the young larvae continue to live in the male's mouth for seven to eight weeks until the yolk sac is totally absorbed. The fry then leave the mouth and become independent.

Adaptation

The bonytongue is an obligate air breather. This means that this fish must gulp air above the water’s surface. It has a specially adapted swim/air bladder, which opens by a duct at the back of the pharynx. Most fish species have a swim bladder. Normally, fish can vary the amount of gas in the bladder, which raises or lowers their body weight, allowing them to easily maintain neutral buoyancy and remain suspended at any given depth of water. Airbreathers, such as the bonytongue, also use the swim bladder to absorb oxygen from the air, thus using it as a supplementary breathing organ. This ability to survive in water with low oxygen content gives air breathing fish two advantages. Firstly, it protects them from those potential predators who are not themselves air breathers. Secondly, it allows them access to potential food sources that are unavailable to non-air breathing fish. Another characteristic of this species is a helical organ on the fourth gill arch which serves as a filter. Water that has already been filtered through the gill-rakers, passes through the helical organ and fine particles, such as phytoplankton, are trapped in mucus and carried back to the stomach.
The bonytongue’s mouth opens upward, an adaptation required because it feeds near the surface of the water. (Bottom feeder mouths are normally on the bottom of the fish, while fish that eat from the middle of the depths usually have mouths located in the middle of their heads). As well, the size and the placement of their fins (with an especially large caudal (tail) fin) give them the ability to jump out of the water to catch airborne prey or avoid capture by larger predators.

Threats to Survival

Asian cultures consider the bonytongue to be a “lucky” species. Apparently, this species resemble the Chinese dragon; metallic scales, barbels, and large pectoral fins, which compares it to “a dragon in full flight “. In addition, positive Feng Shui associations with water and the fish’s red and gold colours make it a popular item for aquariums; it is said that the fish will save the owner from death by dying first. This results in critical over-fishing. However, habitat destruction is likely a greater threat to this species than aquarium collecting because of breeding by hobbyists and aquaculture.

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