Alien pathogens and parasites impacting native freshwater fish of southern Australia: a scientific and historical review

Abstract

Native freshwater fish of Australia have a diverse but largely undescribed endemic pathogen and parasite fauna. However, due to long-shared evolutionary histories and virulence/transmissibility trade-offs, effects of these endemic pathogens and parasites appear to be subtle: significant impacts are rarely observed and epizootics have not been recorded. In contrast, a number of alien pathogens and parasites are now established across southern Australia, causing manifestly harmful effects to native fish species and known or suspected epizootics in native fish populations. Undetected and/or undescribed alien viral pathogens are also suspected of being present. Alien pathogens and parasites were introduced to Australia with imports of live alien fish or their fertilised eggs. A review of the scientific and historical evidence indicates that they have had, and continue to have, greater impacts on native fish species than previously realised—especially for freshwater species. This review also documents a previously unknown, Murray-Darling-Basin-wide epizootic of Murray cod Maccullochella peelii in 1929–30, which may have contributed to strong declines in the related eastern freshwater cod Maccullochella ikei. A serious Chilodonella epizootic of M. peelii in 1982 is also examined. In addition, a possible role for alien viruses of the family Iridoviridae (Ranavirus and Megalocytivirus) in the general decline of the critically endangered silver perch Bidyanus bidyanus, and the rapid collapse of two specific native fish populations—upper Murrumbidgee River B. bidyanus and Shoalhaven River Macquarie perch Macquaria australasica—is suggested. It is argued that the severity of the impact of the virulent alien oomycete Saprolegnia parasitica, both historical and present day, has been underestimated. Finally, action is recommended against emerging new pathogen and parasite threats, and the extreme risk current alien fish importations pose in introducing them. These will further threaten already stressed native fish populations in southern Australia, particularly across the Murray-Darling Basin.

Alien fish ascendancy and native fish extinction: ecological history and observations on the Lower Goodradigbee River, Australia

“…The implication, therefore, is that this alien fish pathogen is another potential factor in the collapse of the silver perch population in Burrinjuck Reservoir and tributaries, including the Lower Goodradigbee River. This reminds us that alien fish impacts frequently extend to alien pathogen and parasite impacts (Kaminskas 2021), in addition to predation, competition and displacement impacts. Other alien pathogens (e.g.…”

“…Conversely, Llewellyn's record/s of alien redfin are earlier than the known invasion timeline for this alien species in these waterways (i.e. 1986) (Lintermans et al 1990;Lintermans 2000aLintermans , 2002Kaminskas 2021).…”

“…Reports of good fishing for Macquarie perch and silver perch continued but again, were generally from the extreme lowest reaches of the river around Wee Jasper, suggesting a predatory and competitive displacement of M Native fish decline continued and by the mid-1980s, remnant Macquarie perch populations in the Lower Goodradigbee were approaching functional extinction, even in the Kashmir/Coodravale/Wee Jasper vicinity, while silver perch underwent a rapid localised extinction in the Lower Goodradigbee as well as Burrinjuck Reservoir and the inflowing Murrumbidgee River (Lintermans 2000a(Lintermans , 2002Frawley et al 2011; Kaminskas 2021). The 1980s also saw further alien fish species in the form of carp and redfin invade the Lower Goodradigbee River via the Murrumbidgee River and Burrinjuck Reservoir (Lintermans 2000a(Lintermans , 2002; Kaminskas 2021), with Llewellyn (1983) possibly sampling some early colonists in the mid-1970s. At present, based largely on rare anecdotal reports, Murray cod persist in the Lower Goodradigbee, but are evidently close to being functionally extinct given their consistent absence in fish sampling results.…”

“…Morgan et al 2002;Barrett et al 2014;Lintermans et al 2014;Wedderburn et al 2014;Brown and Morgan 2015;Wedderburn and Barnes 2016) and have been linked to past declines of Murray cod in the southern Murray-Darling Basin (Rowland 2005(Rowland , 2020. Redfin perch are also the main vector of the alien pathogen Epizootic Haematopoietic Necrosis Virus (EHNV) (Langdon et al 1986;Langdon and Humphrey 1987;Langdon 1989;Whittington et al 1996Whittington et al , 2010, which is a serious threat to some native fish species, although rainbow trout can vector EHNV as well (Langdon et al 1988;Langdon 1989;Whittington et al 1994Whittington et al , 1999Becker et al 2013;Kaminskas 2021).…”

“…Atypical A. salmonicida was presumably brought into the Lower Goodradigbee River by alien carp immigrating from Z www.publish.csiro.au/pc Pacific Conservation Biology Burrinjuck Reservoir. Other possibilities include an origin from contaminated alien trout stockings (Whittington and Cullis 1988;Whittington 1989;Kaminskas 2021), or from contaminated carp or goldfish in an outdoor pond somewhere in the Goodradigbee catchment. It is noteworthy one pool with particularly high numbers of ulcerated carp (Fig.…”