By Jodana Anglesey
Once a popular fish for anglers, Jungle Perch (Kuhlia rupestris) has been in decline for more than 30 years, and wild populations are largely limited to a few areas in northern Queensland.
New research has helped breed the species in captivity and is evaluating the potential to rebuild populations in Queensland through a restocking program.
Jungle Perch can grow to more than 50 centimetres in length and weigh more than three kilograms. They readily take flies and lures and are usually targeted for catch-and-release fishing, which has made them an easy and popular target for anglers.
The species was once found from Cape York down to northern New South Wales. However, in the 1950s and 1960s they began to decline, eventually disappearing altogether from most rivers and streams in the southern part of their range and from the Mackay–Whitsunday Island region.
While they can still be found in northern Queensland, only a few small remnant populations occur anywhere south of Proserpine.
Responding to this decline, three recreational fishing groups – the Freshwater Fishing and Stocking Association of Queensland, the Australian National Sportfishing Association and Sunfish – recognised the need for research to assess the feasibility of a captive breeding and release program to help restore local populations.
This led Queensland Department of Agriculture and Fisheries (DAF) researchers at the Bribie Island Research Centre to begin work on captive breeding of Jungle Perch. Preliminary research focused on verifying past distributions of the species, studying their breeding biology and running preliminary captive rearing trials.
In 2012 the FRDC co-funded a project with Queensland DAF to develop Jungle Perch fingerling production, with the aim of running stocking trials and developing a hatchery production manual. This manual could then be used to scale-up production to commercial quantities if a large-scale restocking program was subsequently recommended and approved.
In 2014 more than 1000 fingerlings were successfully produced. Most of these were released into a Gold Coast hinterland stream, with a smaller batch released into a stream near Mackay. These were the first successful stockings of captive-reared Jungle Perch.
At this stage, Jungle Perch are not an approved species for restocking in Queensland. Last year’s fingerling release trials are an important step in assessing the costs and benefits of restocking as a management measure for the species.
Research leader Michael Hutchison says this was a world first. “The Jungle Perch was once endemic in the Gold Coast region where the fingerlings were released. The stream was selected because it has ideal habitat and no major barriers to prevent their spawning migration.”
The lack of barriers is important because researchers believe that barriers to fish migration, such as weirs, barrages and elevated culverts on rivers in the lower catchment, are a likely contributor to the decline of Jungle Perch. While adult fish prefer to live in clear freshwater rivers and streams with bankside shading, they need to migrate to the ocean to spawn.
After spawning, adults return to fresh water. However, juvenile Jungle Perch first migrate into freshwater when they are 40 to 50 days old and about 18 millimetres in length. Barriers to migration are thought to have disrupted this life cycle.
However, since the 1990s, many redundant structures have been removed from rivers and streams, and fishways have been installed on other barriers.
Several catchment groups including the Mary River Catchment Coordinating Committee, South East Queensland Catchments and Reef Catchments have been restoring stream-side vegetation, the loss of which has also been identified as a cause of dwindling Jungle Perch numbers. Restoration has involved replanting vegetation and installing riparian fencing to exclude livestock.
Prior to release, the captive-reared Jungle Perch fingerlings were conditioned to recognise predators likely to occur at the release site. They were also conditioned to take invertebrate (insect and crustacean) foods similar to those they would encounter in the wild. This conditioning is expected to enhance their capacity to survive.
“We believe this is the first step towards Jungle Perch forming self-sustaining populations in the stream system,” Michael Hutchinson says. “All the stocked fish have been micro-tagged and researchers are now monitoring their progress.”
The breeding program has not been without its challenges. Jungle Perch larvae are difficult to rear in the early stages of development. Standard green-water culture techniques using rotifers, which work well for species such as Australian Bass (Macquaria novemaculeata) and Barramundi (Lates calcarifer), were not successful.
Green-water culture is where a microscopic algae is introduced into the larval rearing tank. The algae provide food for live planktonic organisms on which the larvae feed.
The researchers determined that early-stage Jungle Perch larvae need to be reared on larvae (nauplii) of a type of small planktonic crustacean (copepods) under bright light. Researchers also discovered that Jungle Perch larvae must be reared in full seawater salinities and aeration of the water needs to be gentle during the early stages of rearing.
Several species that spawn at sea and migrate back into fresh water are known to follow the odours of fish from their own species back into suitable streams. If Jungle Perch also use odours as migratory cues, restocking could speed the recovery of Jungle Perch streams by attracting wild fingerlings into restocked sites.
To test the theory that Jungle Perch fingerlings home in on odours, laboratory trials will offer fingerlings a choice of two artificial streams to follow − one with Jungle Perch odour, the other stream without. The experiment will be replicated at least 10 times and odour sources will be rotated to eliminate bias. Ongoing monitoring could also help validate this in the wild.
In 2015 further fingerlings will be produced with the next batch soon to be released into a Sunshine Coast stream. Post-stocking monitoring of the fingerlings stocked in the Gold Coast hinterland has shown encouraging results.
The fish have dispersed over several kilometres of stream and are growing well. Researchers will continue to monitor the progress of the stocked fingerlings to properly document the costs and benefits of the trial stocking program.
Michael Hutchison says if the stocking trials are successful and cost-effective, Jungle Perch could ultimately become an approved species for large-scale stocking in Queensland. Over time, restocking and improved habitat management could help re-establish self-sustaining Jungle Perch populations in the streams where they previously occurred.
This would benefit anglers and regional economies.
“All going well, we would expect that many anglers from southern states would travel to Queensland to fish for Jungle Perch,” he says.
Beyond Australia, Jungle Perch occur in rivers and streams in some of the wetter parts of the Indo-Pacific region. This includes parts of eastern Africa, Madagascar, Mauritius, Reunion, India, Sri Lanka, western Malaysia, Taiwan, the Philippines, southern Japan, New Guinea, New Caledonia, Vanuatu, Fiji and Samoa.
“Jungle Perch have declined in some of these regions also, including in Taiwan and Reunion, and there is interest in restoring populations in those countries.”
Looking to the future, researchers at Queensland DAF’s Bribie Island Research Centre are developing a hatchery production manual, which is expected to be completed by July 2015. Staff are keen to host visits by hatchery operators at the research site to share their knowledge.
The project is supported by the FRDC, with James Cook University and the Freshwater Fishing and Stocking Association of Queensland as project partners.
FRDC Research Code: 2012-213
Michael Hutchison, 07 3400 2037, firstname.lastname@example.org