Counting fish within the sea with out seeing them

By 
Andrea Wild

15 September 2025
3 min learn

There are loads of fish within the sea however how are you going to rely inventory ranges or shield endangered fish with out seeing or catching them?

For analysis scientists Dr Haylea Power and Dr Cindy Bessey from CSIRO, Australia’s nationwide science company, seawater itself holds the reminiscence of what lives beneath the floor.

They’ve been working within the Aquarium of Western Australia (AQWA)’s mesocosm, a large tank full of 3 million litres of seawater to check new methods of detecting fish species and figuring out the presence of particular person fish from the traces they go away behind.

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

 “Mesocosms like ours are laborious to seek out elsewhere. We know precisely what’s within the aquarium, from the 50 species of fish proper right down to the gadgets we feed them, which is why it’s so helpful for science.

“We’re proud AQWA could support this important marine research that will contribute to the understanding and conservation of marine life.”

Collecting DNA from the water

Dr Bessey is a marine ecologist who invents totally different strategies for gathering environmental DNA (eDNA), which is DNA shed into the surroundings by vegetation and animals. Collecting and sequencing eDNA can reveal the presence or absence of a species.

“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 mentioned.

“Our idea was to make marine monitoring faster, cheaper and possible in remote places by developing membranes that could be submerged in seawater to collect eDNA passively.”

Dr Bessey tested her idea in the mesocosm at AQWA, submerging 9 totally different membranes hooked up to an oyster body and analysing the fabric that caught to them.

Surprisingly, she discovered helpful quantities of eDNA might be collected in simply 5 minutes and there was little distinction between utilizing supplies as various as hemp, artificial sponge and filter paper.

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

Counting fish with out wanting

Dr Power develops ways to collect and analyse whole cells that are shed by fish into seawater.

“I use techniques that are normally used to sort blood cells in medical diagnostics. 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 present in the mesocosm,” Dr Power mentioned.

“This new approach means folks will have the ability to use a bucket of seawater to pattern fish for genetic research, as an alternative of needing to catch particular person 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 assessing stock levels of a fished species.”

Dr Bruce Deagle from CSIRO’s Australian National Fish Collection makes use of eDNA to watch the marine surroundings.

“Being able to efficiently capture eDNA from fish and other marine species is in seawater – and also capturing the rich information in whole cells – are key steps that will engage more people working in conservation and fisheries management,” Bruce mentioned.

 

“Testing this expertise in a mesocosm bridges the hole between the doing managed experiments in a lab and actual life science out at sea. It’s wanted to remodel new applied sciences right into a frontline instruments for conservation.”