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Official Magazine of the Nature Society (Singapore)
 
colour paintings of some fishes
Portraits of native fish
An Aquarium in the Wild

Text and illustration by Yong Ding Li
Photos by Robert Khoo

Many of us may have seen Harlequin Rasboras by the hundreds and hoards of dwarf snakeheads swimming around in aquariums and pet shops, but few have admired these aquatic jewels in the streams that snake through the forests of Singapore.
The forest streams in Singapore are home to some 30 species of local freshwater forest fishes, together with many other rare or endangered flora and fauna. These include the endangered Griffiths Cryptocoryne (an aquatic plant) and a host of rare amphibians like the Four-ridged Toad.

typical forest stream in SingaporeThe type of forest where these streams are found is dominated by pandanus, aroids, pitcher plants and rattan palms. The most visible physical character of this type of forest is that the vegetation is partially submerged in acidic water, somewhat like the flooded forest (Igápo) of the Amazon Basin.

In the smaller streams with much rotting vegetation, and therefore low oxygen levels, labyrinthic fish and air-breathing snakeheads are the dominant species, forming almost 100 per cent of the fish fauna. Here, Forest Betta (Betta pugnax) and Croaking Gouramy (Trichopsis vittata) may be found, together with the occasional Two Spot Gouramy (Trichogaster trichopterus) and Malayan Climbing Perch (Anabas testudineus). As the generic name of these fishes suggest, they have nothing to do with the labyrinth of ancient Greek Corinth, but actually refer to the organ found in their gill chamber. This has a maze of membranes which resembles a labyrinth. This organ is a special adaptation for fishes that inhabit poorly oxygenated water. The maze of membranes increases the surface area for absorbing oxygen. These fishes depend so much on atmospheric oxygen for breathing that they will drown if the supply is cut off, for example, by preventing them from reaching the surface of the water.

That partly accounts for their quick darting movements in and out of the rotting leaves at the edges of streams. Their agility also helps them to escape the ferocious jaws of the Dwarf and Black Snakeheads (Channa gachua and Channa melasoma) which are the main predators, apart from dragonfly larvae with an appetite for juveniles or hatchlings.

Spanner Barb
Puntius lateristriga


Banded Coolie Loach
Pangio semicincta


Six-banded Tiger Barb
Puntius johorensis


Harlequin Rasbora
Rasbora heteromorpha


Forest Betta
Betta pugnax


Einthoven's Rasbora
Rasbora einthovenii


Dwarf Snakehead
Channa gachua


Two Spot Rasbora

Rasbora elegans
Swimming in the
forest streams of Singapore


Two Spot Rasbora Rasbora elegans
Einthoven's Rasbora Rasbora einthovenii
Bankan Rasbora Rasbora bankanensis
Harlequin Rasbora Rasbora heteromorpha
Common Barb Puntius binotatus
Spanner Barb Puntius lateristriga
Six-banded Tiger Barb Puntius johorensis
Chemperas Cyclocheilicthys apogon
Grey-banded loach Nemacheilus selangoricus
Banded Coolie Loach Pangio semicincta
Spotted Loach Pangio shelfordi
Hasselt's Catfish Silurichthys hasseltii
Common Walking Catfish Clarias batrachus
Forest Walking Catfish Clarias teijsmanni
Wrinkle-bellied Catfish Glyptothorax major
Little Warty Catfish Parakysis verrucosus
Pygmy Halfbeak Dermogenys pusillus
Forest Halfbeak Hemirhamphodon pogonognathus
Whitespot Aplocheilus panchax
Buff-backed Spiny Eel Macroganthus maculatus
Malayan Climbing Perch Anabas testudineus
Forest Betta Betta pugnax
Croaking Gouramy Trichopsis vittatta
Two Spot Gouramy Trichogaster trichopterus
Pikehead Luciocephalus pulcher
Dwarf Snakehead Channa gachua
Black Snakehead Channa melasoma
Forest Snakehead Channa lucius
Malayan Leaf Fish Nandus nebulosus
Bumblebee Catfish Leiocassis siamensis
Members of the genus Channa are well represented in forest streams, with up to three species present, all of them endangered. In fact, the Black Snakehead was only discovered as recently as 1985. In our forest, the largest of them, sometimes reaching nearly half a metre long, is the Forest Snakehead (Channa lucius). Strangely, the Common Snakehead and the Toman or Giant Snakehead (Channa micropeltes) are only found in the larger reservoirs. I recall hearing some loud splashes coming from a stream, which I thought were caused by tomans, but now believe it was the movement of an otter or false gavial that remains to be discovered. All Channas are predatory, feeding largely on fishes like gouramys and rasboras. Harlequins seem to fall victim to them regularly. Like the labyrinthic fish, they also breathe atmospheric oxygen.
In the large streams and ponds fed by streams, a variety of fishes of the carp family can be seen. Just like wildebeest and zebra on the savannahs, here the dominant fishes are the Two Spot Barb (Puntius binotatus) and the Elegant Rasbora (Rasbora elegans) which occur in medium-sized shoals of 20-50 individuals. These gregarious fishes stay in shoals for protection—safety in numbers work with more pairs of eyes to keep a close lookout for predators as well as to confuse them from focusing on a single prey.

They are the commonest representatives from the cyprinid or carp family in our forests. The Elegant Rasbora is also the largest species of native rasbora here. Closely related to the Two Spot Barb, the Spanner Barb (Puntius lateristriga)

is rather rare here. This species is more of a midwater feeder than the Two Spot which spends a lot of time probing the substrate with its sensitive barbels. Four other species of cyprinids that inhabit streams are the Chemperas (Cyclocheilicthys apogon), Bankan Rasbora (Rasbora bankanensis), Einthoven's Rasbora (Rasbora einthovenii) and the famous Harlequin Rasbora (Rasbora heteromorpha). The last can be found in quite large shoals. Highly popular among aquarists, the Harlequin Rasbora, with its hues of pink, red and silver is perhaps one of the most beautiful native fishes. This interesting fish lays its eggs on the undersides of Cryptocoryne plants. It was actually first discovered in Singapore by an ichthyologist named Duncker in the Botanic Gardens lake.

Not so popular but equally beautiful is the orange-coloured Einthoven's Rasbora. Easily identified and separated from similar Rasboras by its lateral stripe that stretches from the head to caudal fins, this hardy fish is the most wide-ranging Rasbora in Singapore, being the only one to be found on our offshore islands. Occasionally, one may see a fish with six bands on it which bears some similarity to the Sumatran Tiger Barb. This fish is the aptly named Six-banded Tiger Barb (Puntius johorensis), a fish that has a confusing taxonomy. Nevertheless, it is highly prized by collectors and any further collecting will definitely push the species right to the brink of extinction.

Some forest fishes are very difficult to observe in the wild. These are loaches, mostly shy and secretive fishes save for the Grey-banded Loach (Nemacheilus selangoricus). All are also locally endangered. The Banded Coolie Loach (Pangio semicincta) and Spotted Loach (Pangio shelfordi) are aquarium favourites, the same reason that has caused it to be rare in the wild. These fishes are benthic feeders, meaning they feed in the bottom substrate of streams. Given their habits of burrowing into sand and rotting vegetation, it is not surprising to miss them altogether. The beautiful Grey-banded Loach is easier to see as it often forages in the open, in groups of three or four.

'Splish, Splash!' - this sound is one of the first indications of the Common Walking Catfish's (Clarias batrachus) presence. It is the largest native catfish present in our forest streams. The walking catfishes are more catlike than the other three catfish species found in the same habitat in that they can walk on land with the help of their pectoral spines and wiggly bodies, just like the Climbing Perch. They are unfortunately unable to mew or purr like a cat. Two species are found here, the Common Walking Catfish and the endangered Forest Walking Catfish (Clarias teijsmanni). The other three catfish species include the very rare Wrinkle-bellied Catfish (Glyptothorax major), the nocturnal Hasselt's Catfish (Silurichthys hasseltii) and the restricted range Little Warty Catfish (Parakysis verrucosus). The last of this trio is now known to be a new species restricted only to streams in Singapore and Southern Johore.

Ripples that you see on the surface of streams and ponds will draw your attention to a more bizarre type of fish. Halfbeaks, as they are known, have a much longer lower mandible. To visualise this fish, imagine a scissors with half of one cutting end broken off. Being surface feeders, halfbeaks skim for insects that have fallen onto the stream's surface. Halfbeaks are the only native live-bearing fishes. The species most likely to be spotted are the ubiquitous Pygmy Halfbeak (Dermogenys pusillus), a midget shorter than 5 cm, and the much larger and more colourful Forest Halfbeak (Hemirhamphodon pogonognathus).

The terror of fishes, the Pikehead (Luciocephalus pulcher), is like the Pike of European rivers. This is a voracious predator of smaller fishes, especially the diminutive rasboras. A frequent user of 'strategic' ambush tactics, this fish pretends to be a twig (something that it does excellently) and stealthily swims towards its desired meal. When it is close enough, its mouth suddenly throws out a membranous funnel, engulfing the victim and swallowing it whole.

Singapore may not have wild elephants, but it certainly has the elephant fish, the alternative commercial name for the spiny eels. This local icthyological curio has a long sensitive probing nose just like the elephant. This feature allows them to feel for bottom- dwelling prey like prawns, larvae and worms. Shy and nocturnal spiny eels conceal themselves in the thick cover of aquatic vegetation during the day, feeding mostly at night. Two species of Spiny Eels (Macrognathus maculatus and Macrognathus perakensis) have been recorded locally, but the latter may have gone the way of the dodo.

Any leaf that can swim or move around may actually be a fish. The uncannily shaped Malayan Leaf Fish (Nandus nebulosus) looks more leaf-like than fish-like. This natural wonder hunts just like the Pikehead by employing ambush tactics, except it lacks the protractile mouth. It also takes advantage of its cryptic coloration and odd shape to conceal against its predators, like the snakeheads and piscivorous birds.

Our forests offer refuge to some of Singapore's rarest fishes, not forgetting many species of plants, mammals, birds, reptiles and invertebrates. It is a living biological heritage that should deserve more appreciation and recognition than it gets now. In the future, research on the forest may yield even more new and interesting species that might promise cures for some of our diseases. In order for this to happen, the forests and its unique wildlife must be fully protected.

Further reading

  • Kottelat, M., Whitten, A.J., Kartikasari, S.N. and Wirjoatmodjo, S. (1993). Freshwater Fishes of Western Indonesia and Sulawesi. Periplus Editions.
  • Lim, K. K. P. and Ng, P. K. L. (1990). A Guide to the Freshwater Fishes of Singapore. Singapore Science Centre.
  • Ng, H.H. and Ng, P.K.L. (1995). Fishes of the Forest. Nature Watch Vol. 3 No. 2:14-17.
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