ONE of the most popular target species found in our inland rivers and impoundments is the golden perch (Macquaria ambigua), also known as yellowbelly or callop.
These fish are found only in Australia’s inland waters, occurring naturally throughout the entire Murray-Darling drainage basin as far east as the great divide (including the eastward flowing Dawson-Fitzroy system), and as far west as the Lake Eyre basin. In recent years since artificial propagation of the species was perfected, these fish have also been stocked into numerous impoundments, including some outside their natural range.
Golden perch have evolved over millions of years to survive in Australia’s relatively shallow river systems, so fish stocked in impoundments are often exposed to unnatural conditions compared to what these fish historically experienced. One of the main differences they have to cope with in impoundments is increased water depth.
Not so surprising then, were the results of recent studies conducted by NSW Fisheries scientists, who found that golden perch were vulnerable to pressure damage (barotrauma) when they were angled from waters deeper than around 10 metres. They found post release mortality rates for golden perch captured from 2, 10 and 20 metres depth and left untreated were 0 per cent, 4.2 and 19.2 per cent, respectively, three days after capture had taken place.
Fortunately for fish captured from 20 metres, mortality was reduced to 5.6 per cent if they were immediately recompressed (returned to depth by using a release weight).
Even so, many fish retrieved from 20 metres depth also displayed internal injuries like compressed gonads and ruptured swimbladders. Clearly then, it’s important to consider these factors when fishing for golden perch in deep waters – impoundment anglers should carry a release weight at all times to help release undersized fish, and should move elsewhere once they have a feed rather than continue catch and release fishing for deepwater golden perch. Tournament anglers who keep their golden perch in live wells are also encouraged to vent any fish showing signs of excess buoyancy to reduce the stress of confinement as much as possible.
Spawning in golden perch is induced by significant rises in water level once the water temperature is over 20°C. This usually means river dwelling fish are ready to spawn each year from spring throughout the summer months, provided flooding conditions are encountered. Because of their need for this particular combination of conditions, golden perch do not spawn in impoundments.
During a flood, river dwelling adult fish migrate large distances upstream prior to spawning, a behaviour which compensates for the downstream dispersion of eggs and larvae with the current. The species is highly fecund, with females producing up to 300,000 eggs per kg body weight. If flooding does not occur during the spring and summer months, the appropriate spawning triggers aren’t received. The adult fish then resorb their gonads and will not spawn until the next season.
The reasons why the fish spawn during floods is related to the need for an abundant food supply for their larvae and juveniles. Flooding introduces nutrients accumulated on the flood plain into the water. Under normal conditions, the nutrients and increasing water temperatures have a positive effect by triggering plankton blooms which provide the larvae and juveniles with food for survival and growth.
Because the life histories of golden perch and our other native fish are so closely adapted to the natural flooding processes of our inland rivers, their spawning and recruitment are adversely affected by river regulation and man made features such as locks and weirs. These hinder spawning migrations and reduce flood flows, while levee banks reduce the area of floodplain available for juvenile fish nursery areas.
Because of these reasons, it is hoped that populations of wild golden perch and other natives will benefit from the recent efforts to revive the Murray-Darling by allowing sufficient water to remain in the system to mimic environmental flows.
