Flat-head galaxias (Galaxias rostratus) is one of the ‘magnificent six’ native threatened floodplain specialist fish. It’s in dire trouble in the Southern Murray-Darling Basin, having almost declined out of sight.
The species were historically widespread and abundant throughout the Murray River Corridor but are now nowhere to be seen in NSW or South Australia, and only infrequently encountered in Northeast Victoria. It was nationally listed as Critically Endangered in 2016, due to its dramatic decline in distribution and abundance over the last 50 years.
Fish ecologists affectionately dub the species ‘The Ghost Fish’ due to its enigmatic status. If it’s spotted in a billabong or farm dam, which is extremely rare, by the time researchers arrive to investigate, it has disappeared!
The fish are also very fast moving and on the rare occasion where they are seen, it’s usually as a tell-tale bow wave of shimmering water zipping away in front of the seine net or electrofishing wand of even the most agile of fish ecologists.
So what else do we know about the Ghost Fish?
The species prefers still or slow flowing habitats such as billabongs, lakes, swamps, and is also sometimes found in small creeks and rivers. The species also tends to school in midwater and has a diet of macroinvertebrates and zooplankton. There are indications that the species may move upstream in November and December.
The exact reasons for the species decline are unknown, but like most of the magnificent six, it likely includes a combination of river regulation, reduced connectivity of floodplain wetlands, habitat degradation, competition with and predation by invasive fish species, water pollution, and a drying climate.
It’s clear that further work is needed to understand the basic biology and ecological requirements for this species, but even more pressing information to know is, are we too late? Where is this species hiding? Are there any remaining large populations? What can we do to bring this species back?
The time had come to unleash the Ghost Busters!
In recognition that time may be running out, the Tri-State Alliance has commenced a collaborative project to locate and secure the species, as part of the Mid-Murray Floodplain Recovery Reach Program. Project partners at NSW DPI Fisheries have developed an eDNA probe, using fin clips from past collections, as a new tool to track down the Ghost Fish.
eDNA methods involve collecting a water sample, which may contain DNA from a target organism present in the water column (e.g., from tissue, faeces, urine, eggs etc.). The sample is filtered, and the filter paper is preserved and analyzed using a unique genetic probe that can infer presence or absence of the target species at a site.
A key step in the probe development is ensuring that it’s sensitive enough to detect low concentrations of flat-head galaxias DNA. Also, if it’s not specific enough to flat-head galaxias DNA, it runs the risk of picking up closely related species such as obscure galaxias or common galaxias which may share habitats with the ghost fish.
Meanwhile, researchers from the Arthur Rylah Institute (ARI) have narrowed in on the most likely places the species could still be persisting in the Goulburn and Mitta Mitta catchments in northeast Victoria. In April 2022, they undertook physical fish surveys as well as eDNA sample collections at approximately 40 sites, with the aim of confirming that the eDNA probe is an effective tool for detecting the species.
Ghost Fish Found!
Excitingly, ARI staff captured the Ghost Fish at four sites, three in the Goulburn catchment and one in the Mitta Mitta catchment. Encouragingly, one of the populations near Alexandra appears to be sizeable, with 14 individuals captured!
As a bonus, a new Southern Pygmy Perch population was discovered in one of the Goulburn River lagoons.
As well as locating remnant populations, the project has collected important information on Ghost Fish habitat which will help in identifying sites with similar characteristics where the species could thrive as part of future conservation work. It’s also helped refine physical sampling techniques for this overlooked cryptic species.
So, Where to From Here?
Fin clips were collected from 41 individuals. These will be analysed in the coming months to gain information about population genetics and genetic diversity of the species, which will guide future conservation approaches (e.g., keeping populations separate or mixing).
Once the eDNA probe has been deemed ‘field validated’ and effective, the Tri-State Alliance will work with researchers and citizen scientists to search far and wide for additional remnant populations.
The information collected as part of the project will direct protection and management efforts at sites where the species persists and will also guide future conservation advice for the species.
The next steps will be determining how to bring the species back to its former range at scale; this may include captive breeding and/or translocation to suitable ‘surrogate’ habitats or wild sites. Recovery of the Ghost Fish will require ongoing collaboration between researchers, government, community, private landholders, and land managers across three states.
Stay tuned for the next update. We’re hoping that in 10 years’ time, a Ghost Fish may be heard while you’re camping by a billabong…
Main photo: Galaxias rostratus aka Ghost Fish
Source: Dan Stoessel