From the smallest fish in the world, measuring less than a centimetre, to the Tioman stone loach fish, which is found only in a cave on Tioman Island, South-east Asia is a treasure trove of over 3,000 species of freshwater fish - many of which can be found nowhere else in the world.
An international effort, fronted by Singapore researchers, is now under way to assess the conservation status of these creatures.
The team will look at freshwater fishes mainly in the Sundaic region, which includes Peninsular Malaysia, Sumatra, Borneo and Java.
It might seem like a mammoth task, but researchers said it is a critical first step towards conservation for a vertebrate which may not be as appealing as cute or furry animals.
And the effort to assess them comes at a time when many of them are believed to be in decline. Their habitats are cleared for the planting of crops such as rubber and rice. Peat swamp habitats, the only place where many of them are found, have also been drained or cleared to make way for oil palm plantations.
Dr Tan Heok Hui, an ichthyologist (fish expert) and museum operations officer at the Lee Kong Chian Natural History Museum at the National University of Singapore (NUS), said that as freshwater fish is largely regarded as a cheap protein source, there is usually "no heed" paid to their numbers or how environmental degradations could affect them.
INDICATOR OF HABITAT HEALTH
Fish are wonderful bioindicators for the health of habitats after all. If native species are disappearing, then something is very wrong.
PROFESSOR PETER NG, head of the Lee Kong Chian Natural History Museum at NUS.
"Frequently, land developments and transformations affect the aquatic environments, but there is insufficient research to document the events or effects. Many fish species' stock levels have fallen but it is all circumstantial evidence from fisherfolk," said Dr Tan, who is one of the researchers involved in the assessment. "At this juncture, when the IUCN Red List is being done, it may already be too late for some fish species linked intricately to fragile environments."
Widely referred to as a conservation guide, the IUCN (International Union for Conservation of Nature) Red List of Threatened Species aims to provide information on the status of and threats to species.
Peat swamps are habitats that contain highly acidic waters partly because of the peat substrate, which can go to depths of several metres. Fish found in peat swamps tend to be unique to them and nowhere else.
Forest fires also have an impact on these fish populations. They cause nutrification of waters - a process in which water bodies receive an excess amount of nutrients and impact the habitats essential for the fish to thrive, said Dr Tan.
Among those species that are of concern is the Paedocypris, which can be found in the peat swamps of Sumatra in Indonesia and Johor in Malaysia, among other places (see story below).
The Paedocypris progenetica, at 7.9mm for a mature female, holds the title of the world's smallest free-living aquatic vertebrate, and was described by Dr Tan and other international scientists in 2006.
Professor Peter Ng, head of the Lee Kong Chian Natural History Museum, said that while much has been written about the threats facing fish in the Mekong and Chao Phraya rivers, there are other "less publicised" habitats, such as peat swamps and small lakes, that are now under serious threat, including from drainage and reclamation.
"Many of the species have restricted distributions with fastidious habitat requirements," said Prof Ng. "Fish are wonderful bio-indicators of the health of habitats after all. If native species are disappearing, then something is very wrong."
To start with, the team of about 10 international and local freshwater ecology and fish experts have narrowed down a working list of about 1,300 fish species they would like to assess in the Sundaic region.
The status of the species will be assessed based on factors such as population size and distribution, with data taken from published research as well as anecdotal evidence.
In February, an IUCN Red List assessment workshop was organised by NUS, the Lee Kong Chian Natural History Museum and Wildlife Reserves Singapore (WRS), where preliminary assessment of some species was conducted. Experts who attended the workshop came from Switzerland, Indonesia, Malaysia, Germany and Britain. "All are practising taxonomists with varying levels of field experience, with actual practical knowledge of the various fish taxa," said Dr Tan.
The workshop was paid for by the WRS Conservation Fund.
It is estimated that the assessment of 1,300 species will take another three to five years to be completed. The experts have divided the work among themselves according to their areas of specialisation and hope to meet yearly to discuss their progress. Dr Tan, for instance, will be assessing the carp and fighting fish families.
While there are around 20 freshwater fish species of conservation concern in Singapore's natural water bodies, most will not have high conservation value based on the broader context of South-east Asia, Dr Tan said, because they are not endemic to Singapore.
Nonetheless, he stressed that the freshwater swamp and streams within the Central Catchment Nature Reserve and Bukit Timah Nature Reserve are important as more than half of the native freshwater fish are located in those places and nowhere else in the country.
In the long run, the assessment will help provide further insights into Singapore's own aquatic fauna and what can be done to conserve biodiversity here, said Dr Sonja Luz, director of conservation and research at WRS, which runs the River Safari.
"There is a dearth of information on Sundaic freshwater fishes and their associated habitats. Habitat loss is outpacing research efforts to describe and assess them. So there is an urgent need to fill the gaps," she said.
"While many of these miniature fish are no bigger than the average human fingernail, they all play a role in the functioning of ecosystem services."