Fishery biologists and conservationists report that the majority of the region’s large and endangered fish species – including the Mekong giant catfish, giant pangasius, Wallago attu, giant barb, seven striped barb, and giant freshwater stingray – primarily inhabit the deep waters of the Mekong River.

These deep-water areas act as a secure habitat with plentiful food sources.

The pursuit of the largest freshwater fish led to a remarkable discovery in Cambodia on June 14, 2022, when a giant freshwater stingray weighing 300kg and measuring 398cm from head to tail, with a body length of 220cm, was found in a section of the Mekong in Koh Preah commune of Stung Treng province’s Siem Bok district.

Named “Boramey” – full moon – due to its rounded shape by the Wonders of the Mekong, a conservation project funded by the US Agency for International Development (USAID), the stingray was fitted with acoustic tags before its release into the wild.

Over a year later, Boramey earned official recognition from the Guinness World Records as the world’s largest freshwater fish, surpassing the previous record held by a Mekong giant catfish discovered in northern Thailand in 2005.

Scientifically known as Urogymnus polylepis and also referred to in English as the giant freshwater whipray, this species is categorised as endangered on the International Union for Conservation of Nature’s (IUCN) Red List.

Life of Boramey after 2022 release

Wonders of the Mekong project manager Chea Seila disclosed that since its release in neighbouring Kratie province, the team has found that this species does not engage in extensive long-distance migration and has instead been moving between Stung Treng and Kratie provincial border.

This area serves as a crucial habitat, not just for the aforementioned species but also for Mekong Irrawaddy dolphins.

Seila explained that this indicates the creatures’ habitat is in the deep-water regions, which are also home to other fish species, providing favourable conditions for their food sources and a tranquil living environment.

“According to observations by experts who have released stingrays between Siem Bok and other districts, it appears that giant stingrays can also be found in other river areas. However, these stingrays tend to be smaller in size.

“In the Ramsar area of the Mekong, records indicate the presence of giant freshwater stingrays, while local fishermen have reported sightings of stingrays in the Sekong, Sesan and Srepok rivers.

“However, the fishermen claim that the stingrays in these rivers are relatively small. Despite their claims, no photographic evidence or physical samples have been provided,” she said.

Zeb Hogan, a leading fishery biologist with the project, agreed.

“To the best of my understanding, giant stingrays favour free-flowing sections of the Mekong with deep pools and sandy banks. These stingrays appear to remain in the same areas for extended periods, seeking refuge in deepwater reserves and venturing into shallow sandy banks.

“They do not exhibit extensive migratory behaviour – instead, groups of giant stingrays tend to congregate in specific areas, likely for spawning and feeding.

“The Mekong boasts an abundance of giant fish species, surpassing any other river globally. Many giant and endangered fish species trace their origins to the river. Until 2022, Thailand held the record for the heaviest Mekong giant catfish, weighing an impressive 293kg.

“This record was surpassed in 2022 when a 300kg giant freshwater stingray was caught, tagged and subsequently released in Cambodia,” Hogan said.

Guinness World Records

The Mekong, the third-longest river in Asia, extends for around 5,000km from its origin in the Tibetan Plateau. It then traverses Myanmar, Laos, Thailand, Cambodia and Vietnam before flowing into the South China Sea.

“After our team’s measurements, Wonders of the Mekong compiled data, which was then submitted to experts and subsequently presented to Guinness World Records.

“On September 24, an announcement was made by Guinness officially recognising [Boramey] as the world’s largest freshwater fish,” Seila said.

She added that while Wonders of the Mekong has released freshwater stingrays on several occasions – with the group in May successfully identified fish weighing approximately 100kg – Boramey was significantly larger.

“[Boramey] greatly surpasses previously caught fish, which typically weigh around 100kg. This specific stingray weighed a staggering 300kg, earning it the title of the world’s largest,” she said.

Seila also clarified the reason behind the timing of the Guinness World Record announcement on September 29.

“An official announcement was posted on the reference book’s website, but not within the book itself, as the stingray’s discovery occurred after the publication of the Guinness World Records Book for 2023.

“Consequently, [Boramey] will be included in the book in 2024,” she said.

Khim Finan, a spokesperson for the Ministry of Agriculture, Forestry and Fisheries, extends congratulations to the Cambodian giant freshwater stingray for achieving the Guinness World Record.

“We extend our sincere appreciation to Guinness World Records for their official recognition. While not a new discovery, it has now received official acknowledgment.

“Our nation has conserved an important fish species, and this achievement fills us with immense pride, not just within the agricultural sector but across Cambodia as a whole,” he said.

Implementing protection measures

Seila said the Wonders of the Mekong research project team has collaborated with the agriculture ministry’s Fisheries Administration (FiA) to raise awareness about the giant freshwater stingray, disseminating information to the fishing community and those along the river.

They aim to inform people about the giant freshwater stingray, which holds the distinction of being the largest endangered fish in the world.

She added that following the receipt of the Guinness World Record, people should actively participate in spreading awareness.

If a fisherman catches a giant freshwater stingray, they are encouraged to release the fish immediately and report the catch to the research project team.

Such reports help determine the population of giant stingrays, allowing them to measure length and weight and estimate the total number of these fish in nature.

She said it is essential for people to release all stingrays as their numbers and habitats are impacted by pollution and environmental changes with species having been lost or numbers significantly decreased in some countries as a result.

Finan spoke optimistically of Boramey’s impact on future conservation efforts.

“We have installed monitoring equipment for this world record-breaking giant freshwater stingray. Moving forward, I believe that our conservation efforts will be further strengthened.

“The recognition by the Guinness World Records will facilitate enhanced conservation efforts for the world’s largest stingray, especially now that the public is aware.

“Any conservation endeavour requires the involvement of the general public. The attainment of this world record has heightened attention, creating an opportunity to enhance conservation efforts,” he said.