Measuring fish DNA in seawater may lead to quicker survey

Tokyo: Opening the door for quicker and more effective surveys of fish distribution, Japanese researchers have found that measuring quantities of fish DNA released into seawater can reveal how many fish inhabit that environment.

The findings were published online in the journal PLOS ONE.

Until now, the distribution of marine species was calculated using two main methods: fish capture and fish finder equipment. 

However, these survey methods involve heavy costs in time and manpower, and specialist knowledge is required to use the measuring apparatus. 

On the other hand, a method was already available for determining whether the target fish inhabit a certain area of water: analysis of the fish DNA released into the water. 

To take this step further, the researchers tested whether it was possible to discover the location of fish and size of their schools by measuring the amounts of DNA released into the environment (known as environmental DNA, or eDNA).

For the rsearch, a group led by Yamamoto Satoshi from Kobe University, and colleagues collected one-liter samples of surface water and bottom water from 47 locations in Maizuru bay, and estimated the concentration of eDNA of Japanese jack mackerel using real-time polymerase chain reaction (PCR). 

As a result of comparison between the eDNA concentration in the 47 locations and the biomass of Japanese jack mackerel that was simultaneously measured during water collection using fish finder equipment, they discovered that the eDNA concentration of a location reflected the biomass within 10-150 meters of the location. 

This proves that environmental DNA reflects the biomass of the target fish species, and environmental DNA analysis methods can be used to quantitatively measure the distribution and school size of saltwater fish.

This method is simple, requires no specialist knowledge, and can be used for large-scale surveys over a short period of time, the researchers said.