field guide to the freshwater fishes of singapore

Index of fishes
General parts of a fish
Kelvin K P Lim and Peter K L Ng
  Freshwater habitats
Map of freshwater habitats in Singapore

Contrary to popular belief, the freshwater habitat is not as homogeneous as it seems. There are many types of freshwater, each with its own fauna. For convenience, we have recognised several kinds here. It must be emphasised that many of these habitat types gradually merge into each other, and the categorisation used here is purely for convenience. It must also be noted that Singapore's natural environment has altered considerably in the past 100 years, and many areas have been lost to development.

Perhaps the most prominent and obvious to the majority of us are urban habitats, i.e., drains and canals. These habitats are challenging in the sense that there is almost no place to hide, the waters constantly flowing, pollution may be rife, water sometimes very shallow, temperature and pH fluctuations often extreme and predation serious owing to lack of cover. Only the toughest fishes survive. Most are introduced. Typical fauna include tilapia, guppies, mollies and sometimes snakeheads. As increasingly more streams become "upgraded" and "concretised", it must be anticipated that such "immigrant" fishes will spread, always at the expense of native ones.

Reservoirs represent another common source of freshwater for Singaporeans. They consist of two main types, namely the central catchment reservoirs, surrounded by secondary forest, and the estuarine reservoirs which are actually dammed up river mouths. The fauna here is more diverse, but again, many species have been introduced. In the latter type, certain species of euryhaline fishes are thus confined permanently to freshwater. Fish ponds offer a similar habitat. The ubiquitous tilapia is most abundant, as well as snakeheads, eels, labyrinth fishes and some carps.

Of the natural flowing waters, three types may be discerned: open country, secondary forest and primary forest streams. Open country or rural streams are generally more common, but the fauna here is often restricted to the tougher labyrinth fishes, catfish, snakeheads, swamp eels, guppies and mollies. When such streams drain from catchment areas, the diversity is greater, including barbs and rasboras. The habitat in open country streams is generally less predictable, with higher temperatures, greater silt levels and increased risk of pollution. Many streams in the Lim Chu Kang area are intermediate in character, having reasonable shade. The waters, however, tend to have muddy bottoms, and organic pollution as a result of chicken and duck wastes, discourages any great variety of fish life.

The secondary forest streams abound in the catchment area. In the less disturbed areas, more native fishes are present. The fauna here includes barbs and rasboras as well as snakeheads, eels, etc. Interestingly, many of these streams are free of introduced fishes like tilapia and guppies. In the less disturbed areas in the centre of the catchment area, acid water streams and swamps may be found. Singapore's rarest fishes can be found here, most occurring nowhere else. In the least disturbed areas, many of the habitats must have closely resembled what much of Singapore was like a hundred years ago.
photo of a monsoon drain at low water
Monsoon canal

panoramic photo of reservoir

photo of stream under trees
Stream in catchment area

photo of grassy swamp
Acid water swamp forest stream

panoramic photo of stream
Open country stream

photo at high tide
Estuarine area

The last category are the primary forest streams, and these occur only inside Singapore's last patch of primary rainforest, mainly in Jungle Falls Valley. The waters here, however, although pristine and clean, only shelter the Forest Betta. In the drainages at the base of Bukit Timah Hill, some natural ponds can be found. In these, rasboras, barbs and snakeheads still abound.

The estuarine habitat is perhaps the most arduous for fishes which have not overcome their osmoregulation problems. In this habitat, the tides, outflow of freshwater (via drains) and amount of rainfall cause the salinity levels to constantly fluctuate. The unpredictable salt water concentrations encourage euryhaline fishes like scats, mollies and gobies. Tilapias are also common in some areas. Mangrove habitats present similar challenges. Both are considered together under estuarine habitats. The substrate varies from rocky to muddy. Many of these fishes will spend long periods in freshwater, but do better in slightly salty (brackish) waters.
Freshwater habitats
Fishes in Singapore
Amazing Fishy Facts
About the guidebook
From A Guide to Common Freshwater Fishes of Singapore by Kelvin K P Lim and Peter K L Ng
Published by the Singapore Science Centre and sponsored by BP

@Raffles Museum of Biodiversity Research and Singapore Science Centre