Recent weeks have seen the mysterious deaths of more than 70 giant freshwater stingrays in Thailand's Mae Klong River. Officials are not yet certain what killed the enormous fish. Among the possibilities raised thus far include excessive water acidity or poisoning from a recent ethanol plant spill, National Geographic <a href="http://news.nationalgeographic.com/2016/11/70-giant-stingrays-die-mae-klong-river-thailand/">reported</a>. The species (Himantura polylepis) is among the largest fish living in fresh water and can exceed 6 feet wide and 8 feet long and can weigh more than 1,000 pounds. Found in larger rivers in Southeast Asia and Borneo, they eat small fish as well as various crustaceans and molluscs. They're sometimes caught accidentally in fishing lines and are under threat because of issues such as habitat loss due to dam construction and pollution from manufacturing and new construction occurring alongside their rivers. <a href="http://www.seeker.com/stingrays-chew-their-food-like-mammals-2004274358.html">RELATED: Stingrays Don't Just Suck, They Chew</a> The cartilaginous fish are considered <a href="http://www.iucnredlist.org/details/195320/0">endangered</a>, according to the International Union for Conservation of Nature (IUCN) "red list" of threatened species. "Pollution impacts the species in the Thai parts of its range especially...in the Bang Pakong River, 30 specimens were found dead in one day in 2008-9 as a result of a pollution incident," the organization <a href="http://www.iucnredlist.org/details/195320/0">notes</a>. Local wildlife officials have established a "war room" to study whether or not toxic wastewater killed the fish, and Thailand's prime minister has ordered an investigation into the deaths, asiaone <a href="http://news.asiaone.com/news/asia/thai-pm-orders-probe-mass-stingray-deaths?utm_medium=Social&utm_campaign=Echobox&utm_source=Twitter&utm_term=Autofeed&link_time=1476246656#xtor=CS2-4">reported</a>. WATCH VIDEO: How Does Mercury Get Into Fish?

Recent weeks have seen the mysterious deaths of more than 70 giant freshwater stingrays in Thailand's Mae Klong River.

Officials are not yet certain what killed the enormous fish. Among the possibilities raised thus far include excessive water acidity or poisoning from a recent ethanol plant spill, National Geographic <a href="http://news.nationalgeographic.com/2016/11/70-giant-stingrays-die-mae-klong-river-thailand/" target="_blank">reported</a>.

The species (Himantura polylepis) is among the largest fish living in fresh water and can exceed 6 feet wide and 8 feet long and can weigh more than 1,000 pounds.

Found in larger rivers in Southeast Asia and Borneo, they eat small fish as well as various crustaceans and molluscs. They're sometimes caught accidentally in fishing lines and are under threat because of issues such as habitat loss due to dam construction and pollution from manufacturing and new construction occurring alongside their rivers.

<a href="http://www.seeker.com/stingrays-chew-their-food-like-mammals-2004274358.html">RELATED: Stingrays Don't Just Suck, They Chew</a>

The cartilaginous fish are considered <a href="http://www.iucnredlist.org/details/195320/0" target="_blank">endangered</a>, according to the International Union for Conservation of Nature (IUCN) "red list" of threatened species.

"Pollution impacts the species in the Thai parts of its range especially...in the Bang Pakong River, 30 specimens were found dead in one day in 2008-9 as a result of a pollution incident," the organization <a href="http://www.iucnredlist.org/details/195320/0" target="_blank">notes</a>.

Local wildlife officials have established a "war room" to study whether or not toxic wastewater killed the fish, and Thailand's prime minister has ordered an investigation into the deaths, asiaone <a href="http://news.asiaone.com/news/asia/thai-pm-orders-probe-mass-stingray-deaths?utm_medium=Social&amp;utm_campaign=Echobox&amp;utm_source=Twitter&amp;utm_term=Autofeed&amp;link_time=1476246656#xtor=CS2-4" target="_blank">reported</a>.

WATCH VIDEO: How Does Mercury Get Into Fish?

Recent weeks have seen the mysterious deaths of more than 70 giant freshwater stingrays in Thailand's Mae Klong River.Officials are not yet certain what killed the enormous fish. Among the possibilities raised thus far include excessive water acidity or poisoning from a recent ethanol plant spill, National Geographic <a href="http://news.nationalgeographic.com/2016/11/70-giant-stingrays-die-mae-klong-river-thailand/" target="_blank">reported</a>.The species (Himantura polylepis) is among the largest fish living in fresh water and can exceed 6 feet wide and 8 feet long and can weigh more than 1,000 pounds.Found in larger rivers in Southeast Asia and Borneo, they eat small fish as well as various crustaceans and molluscs. They're sometimes caught accidentally in fishing lines and are under threat because of issues such as habitat loss due to dam construction and pollution from manufacturing and new construction occurring alongside their rivers.<a href="http://www.seeker.com/stingrays-chew-their-food-like-mammals-2004274358.html">RELATED: Stingrays Don't Just Suck, They Chew</a>The cartilaginous fish are considered <a href="http://www.iucnredlist.org/details/195320/0" target="_blank">endangered</a>, according to the International Union for Conservation of Nature (IUCN) "red list" of threatened species."Pollution impacts the species in the Thai parts of its range especially...in the Bang Pakong River, 30 specimens were found dead in one day in 2008-9 as a result of a pollution incident," the organization <a href="http://www.iucnredlist.org/details/195320/0" target="_blank">notes</a>.Local wildlife officials have established a "war room" to study whether or not toxic wastewater killed the fish, and Thailand's prime minister has ordered an investigation into the deaths, asiaone <a href="http://news.asiaone.com/news/asia/thai-pm-orders-probe-mass-stingray-deaths?utm_medium=Social&amp;utm_campaign=Echobox&amp;utm_source=Twitter&amp;utm_term=Autofeed&amp;link_time=1476246656#xtor=CS2-4" target="_blank">reported</a>.WATCH VIDEO: How Does Mercury Get Into Fish?

<blockquote>Related on TestTube: <a href="http://testu.be/1MuwtXW">Is Farmed Fish Safe to Eat?</a> <a href="http://testu.be/1JI8ZgJ">Are the Oceans Going to Run Out of Fish?</a></blockquote>High in protein and lower in fat than most other meat, plus packed with heart-healthy Omega 3's, fish is on back on the top of many lists of essential healthy eats. But a number of health experts have warned against eating too much fish for fear that it can cause mercury build up. The only metal that's a liquid at room temperatures, mercury is also highly toxic to most living things. It builds up in the bodies of smaller fish, which get eaten by bigger fish...and so on up the food chain: this process is called bioaccumulation. Mercury bioaccumulates in fish at the top of the food chain like sharks and swordfish. Depending on the how much there is, some can wind up with big doses of the toxin. But many fear that even more common fish like tuna and salmon can accumulate fairly damaging doses, too. Ultimately, the health benefits of fish far outweigh any negatives of mercury bioaccumulation. But it does cause a particularly dangerous risk to pregnant women, potentially harming the brain and nervous system of a developing fetus. A study published in the journal Archives of Pediatrics &amp; Adolescent Medicine has linked mercury exposure to ADHD in children. The FDA recommends that pregnant and breastfeeding women avoid eating shark, tilefish, swordfish and king mackerel, which are particular fish that have shown to have the highest levels of mercury. They also recommended limiting consumption of albacore tuna to just six ounces per week.What about trying to remove mercury from the environment? The challenge is that no one is completely sure where the increase in mercury is coming from? It is a naturally occurring element, but some environmental scientists believe that humans are to blame for the increase. Mercury is a waste product from manufacturing and power plants. While some safeguards have been put in place, there have been numerous, serious leaks or disposal issues. So heavy metals like mercury get released into the air and then find their way into water systems and head out to sea. Corals are really good at filtering out these heavy metals from the water, and a group of Chinese scientists are trying to learn how they do it in hopes they can copy them. Researchers describe their new coral-inspired material in the Journal of Colloid and Interface Science.  So a biomimicry strategy could provide a solution to reducing mercury levels from the oceans, along with green energy and tighter pollution restrictions in order to prevent oceans from being polluted in the first place. Until then, follow the the FDA recommendation of eating at least two meals a week which include fish, but avoiding large species like swordfish.Learn More: <a href="http://www.scientificamerican.com/article/how-does-mercury-get-into/" target="_blank">How Does Mercury Get Into Fish?</a> (Scientific American)"Mercury in the fish we like to eat is a big problem in the United States and increasingly around the world. Mercury itself is a naturally occurring element that is present throughout the environment and in plants and animals."<a href="http://www.eurekalert.org/pub_releases/2015-07/e-scc072315.php" target="_blank">Synthetic coral could remove toxic heavy metals from the ocean</a> (Eurekalert) "A new material that mimics coral could help remove toxic heavy metals like mercury from the ocean, according to a new study published in the Journal of Colloid and Interface Science."<a href="http://www.fda.gov/food/foodborneillnesscontaminants/metals/ucm115644.htm" target="_blank">Mercury Levels in Commercial Fish and Shellfish</a> (FDA)

How Does Mercury Get Into Fish?

Photo: Fishermen in Thailand display an 882 pound (400 kilogram) giant freshwater stingray in 2015. Credit: Youtube/BKK Fishing Tour

Photo: Fishermen in Thailand display an 882 pound (400 kilogram) giant freshwater stingray in 2015. Credit: Youtube/BKK Fishing Tour

Animals

Earth & Conservation

Dozens of Giant Stingrays Found Dead in Thailand

Recent weeks have seen the mysterious deaths of more than 70 giant freshwater stingrays in Thailand's Mae Klong River.

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Dozens of Giant Stingrays Found Dead in Thailand

Experts are probing what might have killed enormous freshwater fish in the Mae Klong River.