Using DNA, Researchers Count 13,000 Fish In Just 2 Pints Of Water Taken From Monterey Bay Aquarium's 1.2 Million Gallon Open Sea Tank

By Ajit Ha on January 15, 2014 5:12 PM EST

Monterey Bay Aquarium
The Monterey Bay Aquarium's Open Sea tank has 1.2 million gallons of water, but researchers only needed 2 pints of water to figure out all the species of fish living inside of it. (Photo: Shutterstock)

Researchers needed just a glass of water from Monterey Bay Aquarium's 1.2 million-gallon Open Sea tank to identify Pacific Bluefin tuna, dolphin fish, and several others from the 13,000 fish present there. This is the first time scientists have used a newly-developed method that analyzes the DNA in a small water sample to help ID species living in the area. Applied out in the real world, it will be a huge improvement over the current techniques, all of which require physical methods like catching animals in nets to determine the species present and their proportion in marine environment.  

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The next logical step in using this modern DNA identification technique will be to census fish in out in the actual ocean, according to Dr. Ryan Kelly, University of Washington assistant professor of marine and environmental affairs, and lead author of a paper in the Jan. 15 issue of PLOS ONE.

An ocean water sample contains a soup of cells shed by organisms that live there, according to Kelly. "Every one of those cells has DNA and if you have the right tools you can tell what species the cell came from. Now we're working to find the relative abundance of each species present," he said in a press release.

This technique is known as "environmental DNA," or "eDNA," and was originally developed two years ago by scientists looking for an endangered species in a river. About a year ago, another group of scientists figured out a way to use the technology to test DNA samples and quickly determine whether the animal in question has a backbone and is a vertebrate. They used molecular probes called "primers" to make it happen. Kelly and his team wanted to take this technique a step ahead, testing the primers to see if they could use them to accurately identify a local community of animals from a small DNA sample.

The researchers chose to use the sea tank at Monterey Bay Aquarium (which is among the ten largest in the world) as a sample area because they were familiar with the species present there and could, therefor, easily judge the accuracy of the technique. DNA data from two pint glasses worth of water revealed to the researchers about eighty bony fishes living in the tank, which tuna and sardines the most prevalent. The results accurately reflected reality. After analyzing the data, the scientists believe that an even smaller sample might have brought them the same result.

The technique was actually so accurate that DNA from a long-dead menhaden fish was picked up. The menhaden never actually lived in the tank - but it had been added to the tank as food for other tank residents. The primer technique was not completely free from biases; it failed to detect two groups of vertebrates in the tank: turtles and the fish with cartilage in place of bones, such as rays and sharks. Kelly suggested that this bias could be solved by designing additional general primers.

Ultimately, the technique could save scientists tons of time and money. By identifying invasive species before they turn into a threat, and also providing ways to look at basic ecosystem functions and food webs, the technique may prove immensely valuable in managing and monitoring aquatic habitats, Kelly said.

There are some challenges: a major hurdle to the application of this technique is the mixing of ocean waters by tides, currents, or other forces in the open ocean. Nevertheless, the preliminary test in Monterey Bay revealed DNA differences between near shore and farther out areas, suggesting that it will likely work out.

Monterey Bay Aquarium photo via Shutterstock.

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