Wastewater-borne DNA reveals endangered species in fish markets

Despite protective measures being in place, endangered fish species are regularly caught then sold in open markets. And while visually searching them out can be difficult, a new technology could more easily allow authorities to know which species are being sold at one location.

Aquatic animals are constantly releasing their DNA into the water, in the form of body fluids, sloughed skin and excrement. This cast-off DNA is known as environmental DNA, or eDNA for short. By taking a water sample from a given geographical location, then determining which species' eDNA is present in that sample, it's therefore possible to ascertain which species are living in the area.

Now, scientists from The University of Hong Kong have utilized the technology to look for endangered species at wet markets. In a recent study, the researchers collected drain water samples from three Hong Kong fish markets, over a five-day period. Tissue, blood and other cellular debris was obtained from those samples via either filtration or precipitation.

When that material was analyzed, it was found to contain the eDNA of protected species such as the brown-marbled grouper, two types of bream fish, and three types of eel. Subsequent visual inspections of the vendors' stalls confirmed that all these species were indeed present.

The problem with relying solely on visual inspections lies partially in the fact that many wet markets are huge, containing a great number of fish that would take a long time to check by eye. Additionally, endangered species are often butchered or sold alongside similar-looking non-endangered species, making them difficult to visually identify.