A team of six scientists from Incheon National University in South Korea has just cracked the code on how to reliably monitor fish in our waters without ever catching a single one. By analyzing 59 carefully controlled experiments across 30 independent studies, Dr. Chang-Bum Jeong and his colleagues have shown that environmental DNA (eDNA) metabarcoding—a technique that identifies fish species from traces of DNA in water—is remarkably effective at answering one critical question: which species are living here?
This matters because knowing which fish species inhabit our waterways is essential for conservation, fisheries management, and detecting invasive species. Until recently, scientists had to rely on traditional fishing nets and trawls, methods that are invasive, labor-intensive, and can stress or harm the very animals being studied. eDNA metabarcoding offers a gentler alternative: researchers simply collect a water sample, extract the DNA fragments fish naturally shed, and identify the species without disturbing them.
But as with all powerful tools, reliability depends on technique. The Incheon team's synthesis review, published in Reviews in Fish Biology and Fisheries, reveals that success hinges on two critical methodological choices. First, which genetic primers the researchers use matters enormously. The team found that primers targeting the 12S rRNA gene—specifically those called Teleo, MiFish-U, and 12S-V5_1—consistently detected fish species and correctly identified them. Second, the quality of the reference database against which researchers compare their results is equally important. Studies that used locally curated DNA barcode libraries achieved substantially higher identification accuracy than those relying solely on public databases.
"eDNA metabarcoding is already highly effective for detecting fish diversity, but its reliability strongly depends on methodological choices such as primer selection and reference database quality," says Dr. Jeong. This finding has immediate practical implications: building comprehensive regional DNA barcode libraries could significantly enhance the reliability of biodiversity assessments worldwide.
The team also investigated whether eDNA metabarcoding could estimate fish abundance and biomass—data that would be invaluable for tracking population health and managing fisheries. Here, the results are more sobering. While the technique excels at answering "which species are present?", sequencing read abundance showed weak relationships with actual DNA concentration across diverse fish communities. This means eDNA metabarcoding cannot yet reliably estimate total biomass in a given area. However, the researchers identified a silver lining: within individual species or closely related groups, the relationship between DNA concentration and sequencing reads strengthens considerably, suggesting the technique could usefully track relative abundance trends in targeted monitoring programs.
As eDNA metabarcoding gains traction globally, these findings offer a practical roadmap. Researchers now understand which primers work best, why reference databases matter, and where the technique's limits lie. By making more standardized methodological choices and investing in regional DNA barcode libraries, scientists can produce more robust results and avoid over-interpreting data. The long-term payoff could be transformative: more reliable biodiversity assessments that support fisheries management, conservation planning, invasive species detection, and ecosystem restoration efforts across the world's waterways.