Scientists are finding new ways to detect and count fish using only the water they swim in. DNA shed by fish can reveal both what species are present and how many individuals are in a location.
Dr Haylea Power and Dr Cindy Bessey from CSIRO are testing these methods at the Aquarium of Western Australia (AQWA). The aquarium’s giant tank holds 3 million litres of seawater and 50 known fish species. This controlled environment allows scientists to check that their techniques work.
Dr Bessey develops tools to collect environmental DNA, or eDNA, which is left behind by fish in water. She tested membranes that can passively collect eDNA. Some membranes are made of hemp, others of sponge or filter paper. They collected enough DNA in just five minutes to identify species. This approach could make marine monitoring faster, cheaper, and possible in remote areas.
Dr Power focuses on collecting whole cells from seawater. She uses techniques normally applied in medical labs to sort blood cells. These cells are sequenced to match them to fish species in the tank. The technique can also distinguish individual fish. This allows scientists to count fish without catching them, helping monitor endangered species or assess commercial stock levels.
Dr Bruce Deagle from CSIRO said capturing eDNA and whole cells is a major step for conservation and fisheries management. Testing in a mesocosm, he explained, bridges lab experiments and real-life conditions at sea. The method could soon become a frontline tool for marine research.