Rare fish rediscovered in Pasir Ris Park; species was first documented in 160-year-old painting

A dog-faced water snake biting a ladder gudgeon. - DARYL TAN

SINGAPORE: When Daryl Tan, an avid photographer of snakes, went on a trip to the mangroves at Pasir Ris Park in June 2023, he made a monumental discovery - a creature that was previously thought to be extinct in Singapore.

Except that it was not a snake, but a fish whose existence was recorded only in a watercolour painting more than 160 years old.

The ladder gudgeon, or bostrychus scalaris, is a rare and little-known fish named for the step-ladder-like banded pattern on its body. French naturalist F. L. de Castelnau first documented the fish via a watercolour painting in a notebook compiled in Singapore between 1858 and 1862.

Tan’s photographs, taken at the mangroves at Pasir Ris Park on June 3, 2023, might be the first photographic evidence of the creature’s existence in Singapore, said Dr Tan Heok Hui, an ichthyologist at the Lee Kong Chian Natural History Museum.

Tan, a 35-year-old educator, has been photographing snakes in Singapore since 2005, and began embarking on more night walks since late 2021 to observe more nocturnal species of snakes.

“That night, I saw that the tide was high so I decided to drop by the mangroves at Pasir Ris Park to see what species of snakes I would be able to find at high tide and when the tide recedes,” he said.

“I was alone and just as I was about to reach the mangroves, I heard a splash and turned to see a flash of white followed by a thin tail.”

At the time, he knew that high tide was a good time for water snakes to hunt for their prey, and figured that one of them had snagged a fish. Moving closer to the source of the splash, he saw a dog-faced water snake biting a fish.

Tan did not know much about fish, but even with his limited knowledge, he could tell it was not a common fish.

Following the encounter, he asked his friends for help to identify the fish, but none were able to. He then posted photos on his Instagram page.

It was only three months later in September 2023 that Lin Jiayuan, a first-year student at Nanyang Technological University (NTU), came across Tan’s post and realised what he had found.

“The ladder gudgeon is an extremely distinctive species despite its elusiveness, because it has a very unique barred body patterning,” said Lin, who is studying bioengineering at NTU.

Although the 22-year-old, who has been interested in fauna, especially invertebrates and fish since he was in primary school, was not able to see the fish’s body clearly at first glance, looking through the rest of the photos helped him identify the specimen.

“After viewing one of the images which showed the fish’s patterning in great detail, I was almost entirely sure of its identity,” he said.

After commenting on Tan’s post, Lin then shared it with two members of staff at the Lee Kong Chian Natural History Museum - Dr Tan, as well as Kelvin Lim, the museum’s curator of amphibians, birds, fishes, mammals & reptiles. Both agreed with Tan’s identification.

Tan and Lin also jointly submitted a Biodiversity Record in the museum’s publication Nature In Singapore, a free, peer-reviewed, online journal which publishes articles on the flora and fauna in the country.

Dr Tan told The Straits Times that such rare sightings are indicative of how much we still do not know of what remains within natural, improved or altered habitats in Singapore.

“(But) once the presence of such uncommon or rare animals is known, efforts can be made to monitor and conserve them. If enough information is gathered, the species can be assessed and their conservation status can be updated on the Singapore Red Data Book, said Dr Tan.

The Singapore Red Data Book provides information such as the scientific and common names and description of each plant and animal species. It uses the same evaluation metrics and references the international conservation status of how threatened a species is, but also assigns a local status for the animal.

Lin told ST that the discovery raises the possibility that other species of fauna, which may have been thought to have died out in Singapore due to habitat loss caused by urbanisation, may still be surviving in remaining mangroves.

This can even be viewed as a “symbol of hope” for not just this species, but other species that share similar habitats but have not been sighted for a long time as well, he said.

“(The discovery) casts into the spotlight how relatively small natural spaces like the mangroves at Pasir Ris Park can still serve as sanctuaries to rare and/or threatened species of wildlife,” said Mr Lin, adding that it highlights the rich biodiversity Singapore still possesses.

“It also serves as a reminder of how disturbance from human activities may have unseen impacts on the ecosystem in such wild spaces - a decline in bird populations will be noticeable, but what about the dying out of a fish that lurks in murky mangrove backwaters, out of sight of most humans?”

Tan, who said he “cannot fully comprehend just how significant this sighting is to the ichthyologists”, noted that there are plans to develop a housing estate near the location of the sighting.

“How that might impact the wildlife in that section of Pasir Ris Park and the mangroves is anyone’s guess,” he said. “If it is negative, then this discovery is all the more significant because it might be the first and last sighting of a bostrychus scalaris.” - The Straits Times/ANN

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Singapore , fish , snake , Pasir Ris , rare , species , ladder gudgeon ,


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