Every Drop Tells A Fishy Story

At first glance, a bucket of seawater from the main tank at the Aquarium of Western Australia (AQWA) might look pretty ordinary. But scientists have just shown that every drop is brimming with secrets — tiny clues that reveal which fish have been swimming by.

Environmental metazoan cells or emCells are whole cells shed into the water by marine animals. These cells contain all the DNA of the animal they came from and thanks to a collaboration with CSIRO, their scientists have discovered new ways to collect and analyse these cells – without disturbing a single fin.

Dr Cindy Bessey and Dr Haylea Power, research scientists from the CSIRO, wanted to improve the way marine environments were monitored which is essential for conserving endangered species and understanding the health of our oceans.

Working in AQWA’s mesocosm, Australia’s largest single aquarium filled with 3 million litres of seawater, they tested new ways of detecting fish species and identifying the presence of individual fish from the minute traces they leave behind in the water.

“The facility at AQWA mimics a natural ecosystem that visitors can experience first-hand from within the underwater tunnel or from above in the glass-bottomed boat,” says Mr Matthew O’Malley, Head Curator at AQWA.

“Mesocosms like this are hard to find elsewhere. We know what’s in that aquarium, from the more than 50 species of fish right down to the food we feed them, which was essential for the research.

We’re thrilled AQWA’s facilities and expertise could help with a discovery that’s as exciting for marine conservation as it is for science.”

Researching techniques for collecting environmental DNA (eDNA), Dr Bessey collected about 80 litres of water straight from AQWA’s mesocosm to test nine different membranes or filters. These were attached to an oyster frame and submerged in the seawater. The material that stuck to the membranes was then analysed.

“At first, people working with eDNA filtered it from many litres of water using pumps, which was slow and required access to a power source,” Dr Bessey said.

Surprisingly, Dr Bessy found enough eDNA could be collected in just five minutes and there was not much difference between the various filters which were made from materials such as hemp, synthetic sponge and filter paper.

“The work at AQWA opens the way to collecting eDNA from remote marine environments and using it to monitor entire ecosystems,” Dr Bessey said.

Dr Power adopted techniques normally used for sorting blood cells in medical diagnostics to analyse the whole cells in the seawater.

“My experiments at AQWA showed that we can use these techniques to sort fish cells from seawater and we validated this by using DNA sequencing to match the cells to the species we know were present in the AQWA mesocosm,” Dr Power said.

“This new technique means people will be able to use a bucket of seawater to sample fish for genetic studies, instead of needing to catch individual fish.

“Importantly, we’ll be able to count the fish present in a location by using DNA to distinguish between individuals. This is important when monitoring an endangered species or checking stock levels of a fished species.”