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  Straits Times 25 May 07
Dangerous aliens lurk in the waters of Singapore
By Christopher Tan, Senior Correspondent

THE Government's plans to open up Singapore's reservoirs for sporting activities may run into a thorny issue.

Freshwater stingrays abandoned by fish hobbyists are believed to be breeding in at least one reservoir: the Seletar. These fish, native to South America, can inflict serious wounds with sharp serrated spines on their tails.

'We have had occasional sightings,' said National Parks Board (NParks) spokesman Jean Lee. 'They are rare, but we've seen them.'

Tropical fish traders say locally caught rays have been turning up regularly in shops here for the past three years. They are supplied by a small group of trappers, who catch them with hook and line. 'If you order 20 fish, they can get them for you within a week,' said the owner of a tropical fish shop. 'That's how plentiful they are.'

Another aquarium shop owner said he sells between five and eight local rays a month. They cost anywhere from $40 for a 10cm wide fish to $120 for a 60cm adult. That is half the price of rays imported from South America.

But they are popular with hobbyists for another reason. The managing director of public-listed fish import/export group Qian Hu Corp, Mr Kenny Yap, said: 'Locally-caught stingrays are usually more hardy than imported ones because they have been conditioned to our environment.'

Although freshwater rays have been available for sale here since the 1980s, they are, in fact, illegal.

The Agri-Food & Veterinary Authority (AVA) bans fish which are venomous or have 'sharp appendages that can cause injury'. AVA spokesman Goh Shih Yong said pet shops are not allowed to sell stingrays as they may pose a danger to the public. 'Action will be taken if a pet shop is found displaying or selling stingrays,' he added.

That is good news to zoologist Peter Ng, who up till recently did not know rays were illegal.

'These fish are nasty,' said Professor Ng, who is director of the Raffles Museum of Biodiversity Research. 'In South America, they are more hazardous than piranhas. People have had limbs amputated because of stingray injuries.'

People are usually stung when they wade near rays or step on them accidentally. They can also be stung while handling caught rays. In Columbia, more than 2,000 cases of stingray injuries are reported a year.

The rays may not be the only exotic fishes in our waters. Prof Ng said there are probably others - either dumped because they outgrew home aquariums, or introduced intentionally by anglers who want new and more challenging prey.

He does not rule out electric eels, electric catfish, arowana and arapaima (one of the world's largest freshwater fish) - all of which are available at aquarium shops here.

Although these can survive here, they are unlikely to breed. In any case, Prof Ng said these fish do not pose as big a danger to humans as rays.

'Electric eels may give you a shock, but they are unlikely to kill you,' he said. 'Unless you have a pacemaker.'

Threats associated with alien species - a term for animals or plants which are not native to a particular ecosystem - go beyond stings and shocks.

An alien species can have a disastrous impact on local life forms. The Nile perch, a big game fish, was introduced into Lake Victoria in East Africa in the 1950s. It caused the extinction of some 200 species in the area.

In recent years, giant snakeheads - called toman here - grabbed headlines when introduced specimens bred and caused havoc in Maryland in the United States. US media dubbed them 'Franken-fish' because of their hardiness and ability to get from pond to pond by crawling for short distances on land.

In Singapore, the toman is one of several dozen alien fish which have established themselves in reservoirs and ponds. Although an expensive food fish and a prized catch for anglers, toman are aggressive carnivores which outcompete local species for food. Often, the locals end up as food. Several years ago, they were in the news when swans in the Botanic Gardens pond were attacked by them.

Dr Tan Heok Hui, curator of fish at the Raffles Museum of Biodiversity Research, said: 'These are foreign talent we don't need.'

He said another big alien has recently arrived: the African walking catfish. Brought in as fingerlings to feed luohan fish a few years ago, some were dumped and are now part of the fauna here. The catfish can grow to one metre in length and has a voracious appetite.

The threat of aliens is something NParks grapples with constantly. On its list of 68 freshwater fish here, 31 are aliens - including guppies and mollies. Two of them - the tilapia and mosquito fish (introduced to control mosquito breeding) - are on the World Conservation Union's list of most invasive species.

NParks spokesman Ms Lee said the list is by no means exhaustive.

Both Prof Ng and Dr Tan do not know what the current count is, but suspect there are more aliens now. They will get a chance to find out.

The Straits Times understands the Public Utilities Board (PUB), which is responsible for Singapore waterways, is commissioning an extensive census of alien aquatic species here. The study, said to span three years and cost more than $2 million, is believed to be the first of its scale here. The PUB would not comment for this report.

Meanwhile, NParks is on to its yearly awareness programme to remind people that releasing animals into the wild is not an act of kindness.

It said these animals may not adapt well to the ecosystem and will die a slow death. Those which have spent time in captivity would have lost their ability to find food.

Alien species may also bring diseases the local population has no immunity against.

Finally, releasing animals into the wild is against the law. Offenders face up to $50,000 in fines, up to six months in jail, or both.

As for alien fish which have already established themselves here, Prof Ng said there is nothing much that can be done about them. That includes the stingray.

'My worry is that some aliens will make it to the Nee Soon swamp,' he said. 'That's where half of all our native fishes are found.'
links
Exotic Species of Singapore blog
Releasing animals: good or bad? a pamphlet used during efforts to educate people NOT to release animals particularly during Vesak Day.
Global Invasive Species Database of the IUCN Invasive Species Specialist Group: introduction to the issue, top 100 worst invasive species and more.
Invasive species weblog updated reports around the world on the impact of alien introduced species.
Invasive species on the Conservation Science Institute: an introduction to this global problem with brief descriptions of major species.

Related articles on Exotic Species and pets
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