THE LAST surviving giant freshwater stingray of those rescued after the mass deaths of more than 50 of the rare fish in the Mae Klong River in October will be returned to its natural habitat this month.
The stingray, nicknamed “Mae Buaban”, is being kept at the Samut Songkhram Coastal Fisheries Research and Development Centre. Authorities say it will be released back into the river when the water quality improves to a safe level and the Fisheries Department officially allows the release.
“We just lost ‘Mae Nongpho’, another giant freshwater stingray, which died on February 13 due to a miscarriage. We also found that Mae Buaban had also lost her babies too, so we have no reason to keep it,” said centre director Kobsak Khetmuan.
“We wrote a letter to the Fisheries Department to ask for permission to return it to the river, as the water quality is now safe. After we receive a letter from the department, we will consult with the provincial governor and people in the province to set up a time and place for releasing the stingray back into the river this month.”
In October last year, more than 50 giant freshwater stingrays were found dead in the Mae Klong River and its tributaries in Samut Songkhram. Only two pregnant giant freshwater stingrays were saved and taken to the centre for treatment.
Both giant freshwater stingrays were recovering and in good condition after intensive treatment for sicknesses related to water pollution. However, both were kept at the centre as officials were worried that the water quality in the river was still too poor for them to survive.
Kobsak said a veterinarian team from Kasetsart University had confirmed that the death of Mae Nongpho was caused by an infection in her blood system related to an unexpected miscarriage.
Low birth rate
“She died very suddenly. First she was healthy and then she stopped eating and died within one day. We found from the preliminary autopsy that there was pus inside her uterus, which indicated infection from the miscarriage. However, the official cause of death for Mae Nongpho is still under examination,” he said.
Following the unexpected death, the veterinarian team examined Mae Buaban and found that she had also lost her offspring. However, she was still healthy.
Nonn Panitvong, a freshwater fish specialist from the Siamensis biodiversity network, said giant freshwater stingrays should not be kept in captivity for long.
“A giant freshwater stingray is a big fish, which is very hard to raise in captivity. This is because of its gigantic size and the large amount of waste that it produces every day. If the pond is too small and does not have a good enough water purification system, the fish will die,” Nonn said.
“Moreover, this kind of stingray lives in deep, turbid riverbeds, so … raising it in shallow, clear water for a long time can make it strain and affect their health, especially pregnant fish which are very sensitive to the changing environment.”
He said both stingrays should have been released as soon as the water quality was safe enough and their health had recovered, adding that after four months in captivity one of the critically endangered species had died.
“We should be very careful when dealing with this kind of rare fish, because the giant freshwater stingray is a viviparous fish and it will take decades for one to be ready to reproduce, so the birth rate is very low and one adult stingray is very valuable to keep the species from extinction,” he said.
Giant freshwater stingray (Himantura polylepis) is an endangered species of stingray found only in the Chao Phraya River Basin, the Mekong River Basin and some rivers in Malaysia. Its numbers are decreasing due to the loss of habitat and increasing water pollution.
It was estimated that the mass death in October killed over two-thirds of the population in the river, which is an important habitat for the fish.