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They have since been translocated across many south-west rivers and dams, and are now among the most widespread exotic species and arguably one of the most voracious predators of native species — readily consuming fish and crayfish up to half their body length. They are considered a class 1 noxious fish in NSW, and in Western Australia they are not allowed to be returned to the water if captured.
They are known to occur in many south-west rivers and streams, tolerant to a range of habitat and water quality conditions. They appear to prefer still or slow-flowing streams and rivers, with large complex shelter e.
Spawn in late winter and spring, laying several hundred thousand eggs amongst aquatic vegetation or woody debris. The egg mass is unpalatable to most other fish. The eggs develop and hatch in about a week. In south-western Australia, males mature in their first year and females in their second year.
This is earlier than reported for most Northern Hemisphere populations and is attributed to their rapid growth rates here because of the warmer climate. They are carnivorous, hunting both individually ambushing or stalking prey or in organised groups herding shoals of small fish into confined areas to be progressively picked off by individuals.
They are voracious predators and territorial, not only eating a wide variety of fish and invertebrates including freshwater crayfish, insect larvae and molluscs but also seen to kill fish that enter their area and leaving them uneaten. Redfin perch were first introduced to Australia in the s for angling. Populations discovered in the upper Hawkesbury-Nepean, Lachlan, Abercrombie and Wollondilly catchments in the last two decades are likely to have been introduced deliberately, as they are geographically isolated from existing populations and could not have spread naturally.
Please note that translocation movement and release elsewhere of any fish without a permit is illegal and heavy fines apply. Redfin perch are voracious predators which consume a wide variety of fish and invertebrates, including small native species such as Pygmy perch, Rainbowfish and Carp-gudgeon, and the eggs and fry of larger fish such as Silver perch, Golden perch, Murray cod and introduced trout. Importantly, as Redfin perch spawn several months earlier than native fishes late winter to early spring , the large schools of predatory Redfin perch fingerlings preying on hatching native fish larvae severely limit recruitment success of native fish.
This predation can seriously impact populations of native species and trout, and hence can also affect recreational fisheries for these species. For example, Redfin perch were recorded as eliminating 20, newly released rainbow trout fry from a reservoir in south-western Australia in less than 72 hours.
Redfin perch are capable of rapidly populating new waterways and in stable water bodies such as lakes and dams they can form very dense populations. Under these conditions, Redfin perch become stunted as they deplete the food supply, becoming worthless for angling. One of the most significant threats to native fish from Redfin perch is their potential to spread the viral disease Epizootic Haematopoietic Necrosis EHN.
This disease, which was first isolated in and is unique to Australia, can cause mass mortality in juvenile redfin perch during the summer months. A number of native species, including mountain galaxias and particularly Macquarie perch, are highly susceptible to the disease, and EHN virus may be one factor responsible for the decline in various native species over the last couple of decades.
Redfin perch are listed as notifiable under the Biosecurity Regulation This listing recognises the threat that this species causes to native fish populations, and prohibits live possession and sale of the species. For more information on the listing of redfin click on the link below. NSW DPI has ongoing survey programs across parts of NSW primarily inland waters of the Murray-Darling Basin which gather information on the distribution of freshwater fish species, including introduced pest fish such as Redfin perch.
The department has undertaken specific surveys to confirm the presence and abundance of Redfin perch in new areas. This will continue following reports of new incursions in other parts of the state.
The results of all this radio tracking, throughout a year, suggest that perch are more active during the winter than was previously thought from the numbers caught in gill-nets. This underscores the importance of perch as a predator of young, plankton-feeding fish in lakes.
Another study compared the feeding behaviour of sizeable perch more than 25 cm long in the Bautzen Reservoir, Germany, a managed lake with less than one percent of weed cover, and in Lake Ring, Denmark, a weedy lake with more than twenty percent of water plant cover. These are obviously two very different types of water body with corresponding huge differences in the availability of food for the resident perch.
Fish were sampled regularly using trawl nets and gill nets to catch them and they were examined to try and find out whether there were any seasonal changes in what they were eating.
The scientists were also interested in whether perch of different sizes had different food preferences in terms of juvenile fish or insects, worms etc. Bloodworms and other similar midge larvae were abundant in both lakes with up to 0ne-thousand five-hundred on every square metre of the bed of Lake Ring but the abundance of young fish was probably higher in the Bautzen Reservoir where there were over six fry per cubic metre of water at the beginning of June.
These two groups of animals were the main food of large perch in both lakes. The average lengths of the fish eaten were consistently smaller than those present in the lake, in other words the perch tended to pick out smaller fish as their prey.
Large perch in the weedless Bautzen Reservoir started to feed earlier on young fish, but this was not related to the size of the available prey fish. Predation on baby fish was certainly greater in Bautzen Reservoir than in Lake Ring. Generally, invertebrates represented the most important food of large perch in the weedy lake, whereas by far the dominant food of large perch in the Reservoir was fish in their first year of life. In other words prey fish availability was an important factor in determining the feeding behaviour of large perch and the nature of what these fish ate differed according to the lake they were living in.
It is well known that, in many waters, individual perch grow at very different rates so that fish of similar age may be much larger or smaller than the general run of fish. Explaining and predicting these differences is not easy and scientists have studied farmed perch to try and solve the problem. It was found that some individual fish were much better competitors than their brothers and sisters when it came to obtaining a meal. The feeding success of young perch in aquaria and their growth rates were consistent, in other words the same particular fish always did well.
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