| Bidyanus bidyanus | |
|---|---|
 | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Perciformes |
| Family: | Terapontidae |
| Genus: | Bidyanus |
| Species: | B. bidyanus |
| Binomial name | |
| Bidyanus bidyanus (Mitchell, 1838) | |
| Synonyms [2] | |
The silver perch (Bidyanus bidyanus) is a medium-sized freshwater fish of the family Terapontidae endemic to the Murray-Darling river system in south-eastern Australia. [3] [4] [5]
The silver perch's scientific name comes from an aboriginal name for the species – bidyan – recorded by Major Mitchell on the Barwon River on his 1832 expedition. [6] (Mitchell's original scientific name for the species was Cernua Bidyana.) Silver perch are not a "true" perch of the genus Perca, but are instead a member of Terapontidae or 'grunter' family. They are the largest member of the Terapontidae, capable of growing in excess of 60 cm (24 in) and close to 8 kg (18 lb), but today wild river specimens are typically 30–40 cm (12–16 in) and 1.0–1.5 kg (2.2–3.3 lb). [3] [4] [5] [6] [7]
The silver perch is the only major representative of the family Terapontidae in the southern Murray-Darling system, compared to northern tropical systems where terapontid species are common. Another small terapontid, the spangled perch (Leiopotherapon unicolor), does occur sporadically in the northern Murray-Darling Basin. [3]
Common names for Bidyanus bidyanus include silver perch, black or silver bream and the aboriginal names 'bidyan' (northern NSW) and 'tcheri/tcheeri' (South Australia). [8]
The silver perch is a large grunter with a small head, small eyes, a small mouth at the end of a pointed 'beak-like' snout. [3] [4] [5] [9] The species is streamlined and laterally compressed, with a spiny dorsal fin of medium height, angular soft dorsal and anal fins and a forked tail. Large specimens become very deep bodied with a large hump behind the head. In terms of colouration, they are dark grey to silvery greyish-brown on the back, silver-grey on the sides, with darker scale margins giving a checkered pattern; the belly is whitish; the dorsal and caudal fins are dark, the pelvic fins white. [3] [4]
Silver perch are opportunistic feeders, feeding on insect larvae, molluscs, annelid worms and algae. [3] [4] [5] [9] The importance of vegetative matter in the diet of silver perch is still debated. Silver perch appear primarily to be a low-order predator of small aquatic invertebrate prey, with occasional intakes of small fish and vegetative matter. [3] [4] In aquaria, silver perch are reported to take blood worms readily.
Silver perch are schooling mid-water fish with a preference for flowing water. [3] [4] [5] Though nowadays found in the lowland reaches of the Murray-Darling system, they originally had a strong presence in the slope and upland reaches of many Murray-Darling rivers as well. [3] In particular, they had a strong presence in upland reaches of the Murrumbidgee River and were originally found as far upstream as Cooma. As recently as the early 1980s, long summer migrations into the upland reaches of the Murrumbidgee were an annual event. [3] [5] Unfortunately these migrations, and these populations, have now collapsed — silver perch are functionally extinct in the Murrumbidgee River now, as in most parts of their former range. [3]
Silver perch have been introduced into the Lake Eyre Basin in arid central Australia. These releases were not officially sanctioned and pose serious hybridisation risks to closely related species of terapontids endemic to the Lake Eyre system.
A translocated and reproducing population of silver perch exists in Cataract Dam on the Hawkesbury-Nepean system. This population was established by NSW Fisheries translocations of juvenile fish from drying billabongs in the lower Murrumbidgee River in approximately 1915–17. [10] [11] The Cataract Dam population is unique in being the only population of silver perch in an artificial impoundment that regularly and successfully recruits and is self-sustaining. [8] The long established prohibition on fishing, the consequent absence of exotic fish and their diseases, and the pristine nature of the dam, including a largely undisturbed, thickly-forested sandstone-dominated catchment and an abundance of coarse rubble and gravel in many inshore areas, where fertilised eggs can settle and not be smothered by silt, are all likely contributors to this unique situation. [3]
Fishermen caught silver perch on unweighted baits such as worms and on small spinning-blade lures in rapids during migrations into upland rivers, as well as flowing and moving waters more generally. They were renowned for being very fast and strong fighting fish.
The [fishing] rod is … used amongst the bream [silver perch] which run up to six pounds, and fight every inch of their way from the time they are struck till they are safely landed. … It is as easy to land a fifteen pound cod as it is a five pound bream, as the latter is notoriously the hardest fighter in our rivers, only being even nearly approached by the catfish. [12]
Male silver perch reach sexual maturity at three years of age. Female silver perch reach sexual maturity at five years of age. [7] Silver perch spawn in late spring and early summer. Originally water temperatures of close to 24 degrees Celsius were considered necessary for spawning to occur [13] but as with all Murray-Darling fish species it has become apparent that the "required" spawning temperature is flexible and that they can and do spawn at lower temperatures. [3] Researchers in the Barmah Forest region of the Murray River have collected drifting fertilised silver perch eggs in water temperatures as low as 17.2 degrees and as high as 28.5 degrees C, between early November and mid-February. Eggs were consistently collected in water temperatures above 20 degrees. [14]
Silver perch are moderately fecund, with egg counts commonly around 200,000 to 300,000. Spawning occurs at the surface at dusk or the first few hours of night. The female sheds the eggs and the male fertilizes them in a few seconds of vigorous thrashing. The eggs are semi-buoyant and will sink without significant current, and take 24 to 36 hours to hatch. [3] [4] [5] [7] [15]
A 1914 account describes a unique observation of silver perch spawning in the wild in the Murrumbidgee River:
The observer of a shoal engaged in distributing ova says: “Between 50 and 70 silver perch were playing—some feeding at the surface and others swimming about apparently aimlessly—in a series of eddies under a precipitous bank of the Murrumbidgee River, at a spot where the water was 10 or 12 foot deep. A section of the shoal, mostly the largest fish, remained in a central position. Suddenly, as though preconcerted, all the fish swam rapidly into a centre, splashing the water, in all directions, and becoming for an instant invisible owing to the agitation of the surface. Next moment the water all around and below the fish had assumed a whitish, opaque tinge, as though a bucket of milk had been thrown in; clearly caused by the extrusion of the milt of the male fish, and its contact with the colourless ova thrown out by the female fish. The operation was repeated five or six times at intervals of about 20 to 30 minutes. Soon after sundown the fish disappeared.” The eggs of the silver perch are demersal and adhere to submerged roots, rushes, &c., in the vicinity of the eddies described. The observer considered what he had seen to be complete evidence of the spawning. [16]
Silver perch continue the trend in native fish of southeast Australia of having high potential longevity. Longevity is a survival strategy in the often challenging Australian environment to ensure that most adults participate in at least one exceptional spawning and recruitment event, which are often linked to unusually wet La Niña years and may occur only every one or two decades. [3] [4] [5] Silver perch can be relatively long-lived; the oldest individual aged so far was sampled from Cataract Dam, NSW (where a vitally important, self-sustaining, translocated population survives) and calculated to be 27 years old through otolith examination, while Murray River fish have been aged to 17 years old. [7] [9] However, recent (2017) research unexpectedly found only a small proportion of silver perch in the surviving Murray River population older than seven years of age. [17] It is not clear if these results are simply the result of extreme blackwater fish kills in the Murray River between 2010 and 2012, the result of some other human/management impact, or a true expression of the species' biology. The latter is doubtful as extensive sampling of the same population in the 1990s found a normal age structure with fish up to 17 years of age. [7] More concerning is the possibility this represents a new impact that is not understood on an already imperilled species, creating a narrowed window of time for breeding and recruitment (recalling females only reach sexual maturity at 5 years of age). The finding has sparked fresh concerns about their conservation in a heavily regulated river system and some changes in management.
As recently as the 1970s, silver perch abounded in the entire Murray-Darling Basin, vast though it is. Since then, however, they have undergone a mysterious, rapid and catastrophic decline. Silver perch have now declined close to the point of extinction in the wild. Based on simple catchment area estimates, the silver perch has disappeared from 87% of its former range. [3] Only one sizeable, clearly viable and self-sustaining population now survives in their natural range, in the central reaches of the Murray River. For these reasons, the Australian federal government has listed wild silver perch as critically endangered under national environmental law. [3] Silver perch are bred extensively in aquaculture but these domesticated strains and captive populations are of little use in ensuring the species' survival in the wild. Such aquacultured silver perch are regularly stocked into numerous artificial impoundments where, without exception, they fail to establish self-sustaining populations.
Reasons for the catastrophic decline of silver perch are only partially understood. Dams, weirs and river regulation and the virtual removal of spring floods appear to have removed the conditions silver perch need to breed and recruit successfully on a large scale. Weirs are also believed to have blocked the migrations of spawning adults and juveniles, which are important to maintain populations over the lengths of rivers. Weirs also kill most drifting silver perch larvae that pass through them, if they are of an undershot design (which, unfortunately, most are). Recent studies that has proven more than 90% of silver perch passing through undershot weirs are killed. [18] [19] And without doubt, weirs trap drifting silver perch eggs (and larvae) as well, where they are either diverted down irrigation offtakes, resulting in eventual death, or sink into fine weir pool sediments and die. [3] [4] [5]
It is not widely appreciated that silver perch eggs sink in still water; [15] silver perch eggs are often inaccurately described as simply being pelagic, or "floating". The eggs may actually settle onto the substrate in the wild and should perhaps be considered benthic in many circumstances rather than pelagic. This may be a factor in their recent serious declines; silver perch may rely on their eggs settling onto clean, well oxygenated substrates of coarse sediments. In this era of flow regulation and flood curtailment by dams, which control the flood events that remove fine sediment, and chronic siltation from poor agricultural practices, the eggs may now frequently land in anoxic fine sediment and organic matter — including in weir pools — and fail to survive. [3] [4] It may be that the section of the central Murray River that supports the last clearly viable natural population of silver perch primarily does so because it supplies a sufficiently long stretch of weir-free river, under standard regulated flows, for eggs to successfully complete their drift and hatch larvae into relatively natural, suitable riverine habitats for survival.
Suspicions are also mounting that there is competition for food between introduced carp and silver perch at larval, juvenile and adult stages. Competition at the larval stage is considered the most serious. Indeed, suspicions are mounting that introduced carp are having very large impacts on a number of native Murray-Darling fish species due to competition at the larval stage, and that these impacts have so far been underestimated. [3] [4] [5]
Exotic pathogens such as EHN virus and possibly similar viruses, introduced via importation of non-native fish, are now strongly suspected of playing pivotal role in the species' decline, and may explain the suspicious, very rapid collapse of some populations (e.g. upper Murrumbidgee). [20] [3]
In a positive development, since 2000, the installation of fishways in many Murray River weirs, so that native fish can pass through them and successfully migrate long distances again, and recent carefully managed environmental flow events, have seen silver perch numbers in the last remaining viable population increase strongly, and seen the population expand slightly in geographic range. [3]
The Murrumbidgee River is a major tributary of the Murray River within the Murray–Darling basin and the second longest river in Australia. It flows through the Australian state of New South Wales and the Australian Capital Territory, descending 1,500 metres (4,900 ft) over 1,485 kilometres (923 mi), generally in a west-northwesterly direction from the foot of Peppercorn Hill in the Fiery Range of the Snowy Mountains towards its confluence with the Murray River near Boundary Bend.
The Murray cod is a large Australian predatory freshwater fish of the genus Maccullochella in the family Percichthyidae. Although the species is called a cod in the vernacular, it is not related to the Northern Hemisphere marine cod (Gadus) species. The Murray cod is an important part of Australia's vertebrate wildlife—as an apex predator in the Murray-Darling River system—and also significant in Australia's human culture. The Murray cod is the largest exclusively freshwater fish in Australia, and one of the largest in the world. Other common names for Murray cod include cod, greenfish, goodoo, Mary River cod, Murray perch, ponde, pondi and Queensland freshwater cod.
The eastern freshwater cod, also known as the eastern cod or Clarence River cod, is a large predatory freshwater fish of the genus Maccullochella and the family Percichthyidae, that occur in the coastal Clarence River system of north-eastern New South Wales. Eastern freshwater cod are closely related to the Murray cod of the Murray-Darling River system, and are considered an icon of the Clarence River system.
The trout cod or bluenose cod, is a large predatory freshwater fish of the genus Maccullochella and the family Percichthyidae, closely related to the Murray cod. It was originally widespread in the south-east corner of the Murray-Darling river system in Australia, but is now an endangered species.
The Murray–Darling basin is a large geographical area in the interior of southeastern Australia, encompassing the drainage basin of the tributaries of the Murray River, Australia's longest river, and the Darling River, a right tributary of the Murray and Australia's third-longest river. The basin, which includes six of Australia's seven longest rivers and covers around one-seventh of the Australian landmass, is one of the country's most significant agricultural areas providing one-third of Australia's food supply. Located west of the Great Dividing Range, it drains southwestly into the Great Australian Bight and spans most of the states of New South Wales and Victoria, the Australian Capital Territory, and parts of the states of Queensland and South Australia.
The Molonglo River is a perennial river that is part of the Murrumbidgee catchment within the Murray–Darling basin. It is located in the Monaro and Capital Country regions of New South Wales and the Australian Capital Territory, in Australia.
The Macquarie perch is an Australian native freshwater fish of the Murray-Darling river system. It is a member of the family Percichthyidae and is closely related to the golden perch.
The golden perch is a medium-sized, yellow or gold-coloured species of Australian freshwater fish found primarily in the Murray-Darling River system, though a subspecies is found in the Lake Eyre-Cooper Creek system, and another subspecies, suspected to be ancestral to all other populations, is found in the Fitzroy River system in Queensland. Other common names for golden perch are "goldens", “yellowbelly” and "callop", the last generally used only in South Australia.
The Australian bass is a small- to medium-sized species of primarily freshwater fish found in coastal rivers and streams along the east coast of Australia. A member of the genus Macquaria from the family Percichthyidae, the Australian bass is an important member of the native fish assemblages found in east coast river systems. It is a native predatory fish and an extremely popular game fish species among anglers. The species was simply called perch in most coastal rivers where it was caught until the 1960s, when the name "Australian bass" started to gain popularity.
The river blackfish is a freshwater fish endemic to the temperate waters of south-eastern Australia. It is found from southern Queensland through to central Victoria, including in the Murray-Darling river system. It is also found in some eastern and southern flowing coastal rivers. Found primarily in upland and "midland" habitats, though early records of fish fauna suggest it was originally far more extensively distributed and was found in some lowland habitats as well. Originally, river blackfish co-inhabited many of its lowland and "midland" habitats with species such as Murray cod and golden perch, and its upland habitats with species such as trout cod and Macquarie perch. It is a popular angling fish in some parts of its range.
The eel-tailed catfish, Tandanus tandanus, is a species of catfish of the family Plotosidae. This fish is also known as dewfish, freshwater catfish, jewfish, and tandan.
The Brisbane River cod was a unique form of Maccullochella cod that occurred naturally in the Brisbane River system, an east coast river system in south east Queensland, Australia. The Brisbane River Cod was known as the Bumgur by the Jinibara people centred in the Kilcoy region and the junction of the Stanley and Brisbane Rivers. Their exact taxonomic status is not known, but based on several genetic studies it is suspected that Brisbane River Cod were a species intermediate between eastern freshwater cod of the Clarence River and Richmond River systems in northern New South Wales and Mary River cod of the Mary River in central Queensland.
The Queanbeyan River, a perennial stream that is part of the Molonglo catchment within the Murray–Darling basin, is located in the Monaro and Capital Country regions of New South Wales and the Australian Capital Territory, in Australia. The river is 104 kilometres (65 mi) in length with a catchment area of 96,000 hectares. The Queanbeyan River and the Cotter River meet the potable water supply needs of the Canberra and Queanbeyan region and whose water quality is specifically protected under Federal legislation.
Agassiz's perchlet, also known as Agassiz's glass fish and the olive perchlet, is a species of ray-finned fish in the family Ambassidae. It is semi-transparent with dark scale edges forming a pattern over most of the body. It grows to a maximum of 7.5 cm. It is a macrophyte spawner with adhesive eggs. It is endemic to Australia. It was named for the zoologist Louis Agassiz.
The yellowtail trumpeter is a common species of coastal marine fish of the grunter family, Terapontidae. The yellowtail trumpeter is native to Australia and Papua New Guinea, ranging from Cape Leeuwin in Western Australia along the north coast to Bowen, Queensland, and along the southern coast of Papua New Guinea.
Scottsdale Reserve is a 1,328-hectare (3,280-acre) nature reserve on the Murrumbidgee River in south-central New South Wales, Australia. It is 79 kilometres (49 mi) south of Canberra, and 4 kilometres (2.5 mi) north of Bredbo. It is owned and managed by Bush Heritage Australia (BHA), which purchased it in 2006. The purchase was supportive of projects aiming to connect existing fragmented remnant habitat such as K2C. Since the 1870s up until 2006, the land was used for agriculture – primarily sheep grazing with some minor cropping. A significant component of the Reserve has been cleared of native vegetation.
The Menindee Lakes is a system of 9 large, but relatively shallow lakes, located in south-west New South Wales on the Darling (Barka) River, about 200 km upstream of the Darling River's junction with the River Murray. The Darling River is fed by nine major tributary river systems flowing from south-east Queensland and north and central NSW. The town of Menindee is close to the lakes and the nearest city is Broken Hill.
The New South Wales Central Murray Forests lie on the floodplain of the Murray River in the Riverina region of south-central New South Wales, Australia. On 20 May 2003 the forests were recognised as a wetland site of international importance (RS1291) by designation under the Ramsar Convention on Wetlands.
Bidyanus welchi, commonly known as Welch's grunter, black bream, or silver bream, is a species of freshwater ray-finned fish from the family Terapontidae native to Australia.
The Cumbung Swamp, also known as the Great Cumbung Swamp, is a wetland made up of the ecosystems surrounding the junction of the Murrumbidgee and Lachlan Rivers in the South West Region of New South Wales. When it is at full capacity, the swamp supports a large population of migratory waterbirds as well as one of the largest reed swamps in the Murray Darling Basin.
