A fish so rare it had not been seen in Hong Kong waters for a full decade has been detected again, not by a net or a diver, but by a cup of seawater.
Scientists used a technique called environmental DNA tracking to find the Tai O fish, a species named after the historic fishing village on Lantau Island. The discovery marks the first confirmed presence of the fish in local waters since 2014.
A vanishing fish from a vanishing village
The Tai O fish, known locally as the "Tai O fish," once thrived in the brackish waters near the stilt house community of Tai O. Overfishing, habitat loss and pollution had pushed the species to the edge of local extinction. For years, fishermen and researchers came up empty. The fish became a symbol of what had been lost from the area’s once rich marine life.
Researchers from the University of Hong Kong and the Agriculture, Fisheries and Conservation Department teamed up to search for the fish using a method that does not require catching a single specimen. They collected water samples from various spots in Hong Kong’s western waters and filtered them for traces of genetic material shed by fish and other organisms.
How a glass of water can find a ghost fish
Environmental DNA, or eDNA, works because all living things leave tiny genetic traces in their surroundings. Skin cells, mucus and waste all drift in the water. By analyzing these traces, scientists can identify which species have passed through an area without ever laying eyes on them.
The team found the Tai O fish’s genetic signature in samples taken near its historical habitat. The detection does not mean the fish is back in large numbers, but it proves that at least some individuals still survive in Hong Kong waters. The finding gives conservationists a starting point for protection efforts.
Local residents in Tai O had long hoped the fish would return. The village, famous for its stilt houses and traditional fishing culture, has seen its marine resources dwindle over decades. For many older villagers, the Tai O fish was a staple of childhood meals and a marker of the area’s ecological health.
The discovery does not guarantee the species will recover. But it shows that even a fish thought to be locally extinct can still be hiding in plain sight, leaving its invisible signature in the sea.
