Non-Invasive DNA Testing to Tell How Many Fish There Are in the Water

The new method for counting fish is comparable to that of a quantitative echo sounder method.
Loukia Papadopoulos

All natural bodies of water contain DNA belonging to living entities such as animals and plants. Would it then be possible to test the DNA of water to find out how many of these organisms live there? Ecologists seem to believe so.


They have begun to actively analyze water-based DNA molecules, called environmental DNA, to assess the distribution of macro-organisms. As such, researchers from the National Institute for Environmental Studies, Tohoku University, Shimane University, Kyoto University, Hokkaido University, and Kobe University, have revealed a new method for estimating fish population abundance by simply measuring the concentration of environmental DNA in the water. 

This is because organisms present in water release (or shed) DNA molecules and the water eventually transports and degrades them. However, the new method is not fool-proof as all these processes are undertaken in a complex way.

"This complicates and limits the traditional approach of population quantification based on environmental DNA where the presence of a definite relationship between the concentration of environmental DNA and population abundance has been critical, "explained in a statement Keiichi Fukaya, research associate at the National Institute for Environmental Studies and the lead author of the paper.

"We thought that these fundamental processes of environmental DNA, the shedding, transport, and degradation, should be accounted for when we estimate the population abundance through environmental DNA," he said.

The researchers then adopted a numerical hydrodynamic model that accounts for the processes to mimic the distribution of environmental DNA concentrations within a natural water body. Fukaya explained that by solving this model in the 'inverse direction', his team could estimate the fish population based on the distribution of environmental DNA concentrations.

For now, the method seems to be working. A case study from Maizuru Bay, Japan, revealed that the estimate of the population of Japanese jack mackerel (Trachurus japonicus), achieved by Fukaya's method, was similar to that of a quantitative echo sounder method.

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