DNA Detectives Able to ‘Count’ Thousands of Fish Using as Little as a Glass of Water

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Newswise A mere glass full of water from Monterey Bay Aquarium's 1.2 million-gallon Open Sea tank, among the 10 largest aquariums in the world, is all scientists really needed to identify the Pacific Bluefin tuna, dolphinfish and most of the other 13,000 fish swimming there.

Researchers also for the first time used DNA from water samples to discern which of the species were most plentiful in the tank.

Being able to determine the relative abundance of fish species in a body of water is the next step in possibly using modern DNA identification techniques to census fish in the open ocean, according to 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.

Currently most scientists net, see or in other ways count fish to determine what species are present and in what proportions in marine environments.

"It might be unpleasant to think about when going for a swim in the ocean, but the water is a soup of cells shed by what lives there," Kelly said. Fish shed cells from their skin, damaged tissues and as body wastes.

"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.

It was barely two years ago that an influential paper was published by scientists who determined the presence of an endangered species they were seeking in a river using this "environmental DNA" or "eDNA." Since then the technique has been used to look for other specific species in both freshwater and one marine setting.

"Clearly this is an effective tool in the wild when you know what you're looking for," Kelly said.

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DNA Detectives Able to 'Count' Thousands of Fish Using as Little as a Glass of Water