Grace Chua, Straits Times 25 Mar 10;
IT IS official: Freshwater stingrays the size of dinner plates are breeding in at least one Singapore reservoir.
These barbed Motoro stingrays, native to South America, are lurking in the Upper Seletar Reservoir where sport fishing, kayaking and boat rides are allowed.
These fish, likely to have been released into the reservoir by fish hobbyists, can deliver venomous stings that can cause extreme pain and even death.
But national water agency PUB, the custodian of reservoirs, said that to date, there have been no reports of stingray injuries in Upper Seletar. Still, it advises kayakers to wear protective footwear and to launch their boats from a concrete pontoon instead of the shore.
PUB also urged fish hobbyists not to release non-native animals into the reservoir because, injuries aside, these creatures can upset the food chain there by feeding on native species, out-competing them for food and spreading diseases to which the local species are not immune.
Examples of non-native species that have established themselves in Singapore include the toman or snakehead fish and the African walking catfish, both of which are voracious and aggressive.
Toman made the news in 1991 when they attacked the young swans in Botanic Gardens.
Local anglers and park staff have thus far known of the Motoro stingrays only anecdotally, but scientists from the National University of Singapore's Raffles Museum of Biodiversity Research have netted and identified them.
Their scientific paper, published late last year in the journal Biological Invasions, is the first record of these South American rays establishing a colony this far from their home in the Amazon.
The rays seem to have adapted well to life in the reservoir: The scientists' haul of five of these disc-like fish included two pregnant females.
What is to be done, now that they seem to have dug in and multiplied?
Biologist Peter Ng, one of the authors of the paper, said when alien species establish themselves, they cannot be eradicated overnight, 'so we need to be proactive and plan ahead'.
In their paper, the scientists recommended fishing or trapping the rays, educating the public on the danger of releasing non-native species into the wild and teaching people how to avoid injuries.
Recreational angler Tan Tien Yun, 28, who has seen people catch stingrays using live bait, said of the creatures' hunting style: 'Stingrays are ambush predators. They sit around where prey is likely to be, and when prey passes by, wham!'
When they are not hunting for food, these naturally shy creatures attack only when they feel threatened.
These rays are themselves snared for the pet trade. Since the mid-1990s, various species of freshwater rays have been popular with freshwater-aquarium keepers.
Adult Motoro rays can cost as much as $150 each, grow to more than 30cm in diameter and measure nearly a metre from head to barbed tail.
Since 2004, it has been illegal for pet shops to display and sell stingrays and other venomous fish or fish with spines, said the Agri-Food and Veterinary Authority (AVA).
Shops caught selling such fish can be fined $100.
But the ban does not apply to fish farms, which import the fish for re-export.
They are allowed to sell these fish to individual hobbyists who know how to handle them and are told not to release them into the environment, the AVA explained.