Eleven of the 18 freshwater stingrays living at the U.S. National Zoo died over the holiday weekened, together with two arowanas. All dead fishes were residents of the zoo’s Amazonia exhibit; a 55,000-gallon (208,000 L) aquarium designed to replicate a flooded Amazon forest. Zoo officials are now suspecting low oxygen levels to be behind the sudden mass death.

Picture of Motoro Sting Ray, Ocellate river stingray – Potamotrygon motoro. Not one of the dead rays.
Copyright www.jjphoto.dk

As soon as the deaths were discovered 7 a.m Monday morning, zookeepers tested the water and found low levels of dissolved oxygen. They immediately started supplementing the aquarium with reservoir water and no more fish have died so far. In addition to stingrays and arrowanas, the Amazon aquarium is also home to discus, boulengerella fish, and a large school of guppies. By 10:15 a.m. Monday, the oxygen levels were back to normal but zookeepers continue to monitor the health of the surviving fish just in case.

Necropsies performed on the dead fish did not unveil any definite cause of death, which makes low oxygen levels even more likely, according to National Zoo officials. They do not believe human error caused the oxygen drop, since all protocols and checks were properly followed Sunday night.

Insufficient levels of dissolved oxygen in the water are one of the most common causes of fish mass death, in the wild as well as in captivity. Last year, 41 stingrays died at the Calgary Zoo in Canada due oxygen scarcity in the water.

According to Wildlife Extra, 12 different specimens of the endangered Giant freshwater stingray were caught in over the course of just 3-4 months last year. The findings where made in both the Ban Pakong and the Maeklong Rivers, and one of the specimens was a young stingray measuring no more than 12 cm (4.7 inches). This might be a sign that the Giant freshwater stringray is somehow managing to combat the dangerous pollutions that are contaminating its habitat.

The specimen that received most attention was of course the enormous stingray caught by Tom Parker from Coventry whilst on a guided fishing tour to the Ban Pakong River. After being measured and photographed, the rare fish was fortunately released back into the wild. The Giant freshwater stingray had a wingspan of 2.4 meters (7.9 feet) and weighing it turned out to be impossible for the fishing party.

A research project has now been launched by Dr Terry Bertozi of the Evolutionary Biology Unit of the South Australian Museum in Adelaide, Australia and the fishing company FishSiam in order to find out more about the elusive Giant freshwater stingray.

You can learn more reading the full article at Wildlife Extra: http://www.wildlifeextra.com/giant-stingray930.html

Stingrays have flat bodies that make it possible for them to stay hidden in under layers of sand at the bottom until an unsuspecting animal ventures close enough to become lunch. Some stingrays grow really huge, as the one in the article, but others can be kept in normal hobby aquariums. It is very important to provide them with a suitable substrate in the aquarium to allow them to carry out their natural habits. You can learn more about a few species of stingray that can be kept in aquariums here: http://www.aquaticcommunity.com/predatory/sting.php