Macquarie Perch Research Articles

Immediate Genetic Augmentation and Enhanced Habitat Connectivity Are Required to Secure the Future of an Iconic Endangered Freshwater Fish Population.

Genetic diversity is rapidly lost from small, isolated populations by genetic drift. Measuring the level of genetic drift using effective population size (N e) is highly useful for management. Single-cohort genetic N e estimators approximate the number of breeders in one season (N b): a value < 100 signals likely inbreeding depression. Per-generation N e < 1000 estimated from multiple cohort signals reduced adaptive potential. Natural populations rarely meet assumptions of N e-estimation, so interpreting estimates is challenging. Macquarie perch is an endangered Australian freshwater fish threatened by severely reduced range, habitat loss, and fragmentation. To counteract low N e, augmented gene flow is being implemented in several populations. In the Murrumbidgee River, unknown effects of water management on among-site connectivity impede the design of effective interventions. Using DArT SNPs for 328 Murrumbidgee individuals sampled across several sites and years with different flow conditions, we assessed population structure, site isolation, heterozygosity, inbreeding, and N e. We tested for inbreeding depression, assessed genetic diversity and dispersal, and evaluated whether individuals translocated from Cataract Reservoir to the Murrumbidgee River bred, and interbred with local fish. We found strong genetic structure, indicating complete or partial isolation of river fragments. This structure violates assumptions of N e estimation, resulting in strongly downwardly biased N b estimates unless assessed per-site, highlighting the necessity to account for population structure while estimating N e. Inbreeding depression was not detected, but with low N b at each site, inbreeding and inbreeding depression are likely. These results flagged the necessity to address within-river population connectivity through flow management and genetic mixing through translocations among sites and from other populations. Three detected genetically diverse offspring of a translocated Cataract fish and a local parent indicated that genetic mixing is in progress. Including admixed individuals in estimates yielded lower N e but higher heterozygosity, suggesting heterozygosity is a preferable indicator of genetic augmentation.

Planning and implementing genetic rescue of an endangered freshwater fish population in a regulated river, where low flow reduces breeding opportunities and may trigger inbreeding depression.

Augmenting depleted genetic diversity can improve the fitness and evolutionary potential of wildlife populations, but developing effective management approaches requires genetically monitored test cases. One such case is the small, isolated and inbred Cotter River population of an endangered Australian freshwater fish, the Macquarie perch Macquaria australasica, which over 3 years (2017-2019) received 71 translocated migrants from a closely related, genetically more diverse population. We used genetic monitoring to test whether immigrants bred, interbred with local fish and augmented population genetic diversity. We also investigated whether levels of river flow affected recruitment, inbreeding depression and juvenile dispersal. Fish length was used to estimate the age, birth year cohort and growth of 524 individuals born between 2016 and 2020 under variable flow conditions. DArT genome-wide genotypes were used to assess individual ancestry, heterozygosity, short-term effective population size and identify parent-offspring and full-sibling families. Of 442 individuals born after translocations commenced, only two (0.45%) were of mixed ancestry; these were half-sibs with one translocated parent in common. Numbers of breeders and genetic diversity for five birth year cohorts of the Cotter River fish were low, especially in low-flow years. Additionally, individuals born in the year of lowest flow evidently suffered from inbreeding depression for juvenile growth. The year of highest flow was associated with the largest number of breeders, lowest inbreeding in the offspring and greatest juvenile dispersal distances. Genetic diversity decreased in the upstream direction, flagging restricted access of breeders to the most upstream breeding sites, exacerbated by low river flow. Our results suggest that the effectiveness of translocations could be increased by focussing on upstream sites and moving more individuals per year; using riverine sources should be considered. Our results indicate that river flow sufficient to facilitate fish movement through the system would increase the number of breeders, promote individuals' growth, reduce inbreeding depression and promote genetic rescue.

Multi-decadal trends in large-bodied fish populations in the New South Wales Murray–Darling Basin, Australia

Context Native fish populations in Australia’s Murray–Darling Basin (MDB) have experienced severe declines since European settlement. Information on their status is needed to guide management and recovery. Aims To quantify trends in MDB fish populations in New South Wales (NSW) from 1994 to 2022. Methods Relative abundance, biomass, and size structure were examined using generalised additive mixed models at NSW MDB and river catchment (valley) scales for five native species (Murray cod, Maccullochella peelii; golden perch, Macquaria ambigua; silver perch, Bidyanus bidyanus; Macquarie perch, Macquaria australasica; freshwater catfish, Tandanus tandanus) and one alien species (common carp, Cyprinus carpio). Key results There was strong inter-annual variation in relative abundance, biomass and population structure for all species. At the Basin scale, relative abundance of Murray cod, golden perch and common carp increased across the time series, with no clear trends for silver perch, Macquarie perch or freshwater catfish. Patterns in relative abundance, biomass, and population structure were variable among valleys for most species. Conclusions and implications Although native fish populations in the MDB remain degraded and face escalating threats, recent increases in the abundance of some native species are an encouraging sign that integrated restoration efforts can improve the outlook for native fish.

Recombinant luteinizing hormone as a tool towards understanding reproductive dysfunction in captive Macquarie perch Macquaria australasica

The Macquarie perch Macquaria australasica is an endangered freshwater fish endemic to the Murray-Darling Basin in Australia. Captive breeding is considered an essential measure to save the species from extinction, yet its reproductive biology is not fully understood. We produced a recombinant single-chain Macquarie perch luteinizing hormone (rmpLh) in the methylotrophic yeast Pichia pastoris, confirmed by Western blot analysis and mass spectrometry. We developed and validated a heterologous competitive enzyme-linked immunosorbent assay (ELISA) for M. australasica Lh using antibodies generated against the giant grouper Epinephelus lanceolatus Lhb, which is 91% identical to the M. australasica sequence at the amino acid level. Measurement of Lh in plasma samples collected at 2 timepoints (June vs. August 2020) from captive F1 broodstock did not show a significant difference. Plasma Lh in samples from wild fish collected in September 2020, a month prior to the spawning season, were almost 10-fold higher than those of the F1 broodstock. The tools generated here will help us to understand the reproductive biology of M. australasica and develop reliable assisted reproduction techniques for the species.

Establishing new populations in water-secure locations may benefit species persistence more than interventions in water-stressed locations

The effects of climate and land-use change, coupled with limited management resources, mean that managers are increasingly faced with decisions to invest in some locations at the expense of others. Given their potentially controversial nature, such decisions require predictions of likely outcomes under different management strategies and potential future climates. We develop an approach to prioritise management interventions across multiple locations in highly variable and uncertain environments, using a stochastic model of population dynamics structured to include the (dynamic) effects of environmental conditions on key vital rates. We demonstrate this approach with a case study on the endangered Australian freshwater fish, the Macquarie perch (Macquaria australasica), assessing the effectiveness of seven management interventions under five scenarios of deterministic climate change. All management interventions were predicted to improve Macquarie perch population outcomes (increased abundances, reduced risk of quasi-extinction), with the risk of declines lowest when management included augmented gene flow and enforcement of fishing regulations. The lowest levels of risk occurred in locations with stable environmental conditions, which suggests that reintroducing Macquarie perch to large, regulated rivers with suitable access to spawning habitat may be more beneficial than investment in small, unregulated streams where populations were unlikely to persist under any scenario. Population reintroductions provide opportunities to shift populations from water-stressed to water-secure locations where required (e.g. to preserve unique genetic diversity). This finding likely applies to many aquatic species, and highlights a potential need to supplement threat mitigation in water-stressed locations with efforts to establish new populations in water-secure locations.

Strong bidirectional gene flow between fish lineages separated for over 100,000 years

Restoring levels of genetic diversity in small and declining populations is increasingly being considered in biodiversity conservation. Evidence-based genetic management requires assessment of risks and benefits of crossing populations. Because risks are challenging to assess experimentally, e.g. through multi-generational crosses, decision-support approaches utilize proxy risk factors such as time since separation of lineages. However, the paucity of empirical datasets on fitness consequences of longer separation times tends to favour crossing lineages with conservatively short separations, restricting wildlife managers’ options. Here, we assessed the genetic outcomes of interbreeding in the wild between lineages of a threatened Australian freshwater fish (Macquarie perch) separated by an estimated 119,000–385,000 years of evolution in distinct environments. Fish belonging to the Murray-Darling Basin (MDB) lineage escaped from Cataract Dam—into which they were translocated in ~ 1915—into the Cataract River, where they interbred with the local Hawkesbury-Nepean Basin (HNB) lineage. Analyses of reduced-representation genomic data revealed no evidence of genetic incompatibilities during interbreeding of the two lineages in the Cataract River: assignment to genotypic clusters indicated a spectrum of hybrid types including second generation hybrids and backcrosses to both parental lineages. Thus, no adverse effects were detected from genetic mixing of populations separated by > 100,000 years. We are not advocating purposely crossing the two lineages for management purposes under present cost–benefit considerations, because there are currently sufficient intra-lineage source populations to beneficially mix. Instead, this study presents a useful calibration point: two morphologically different lineages evolved in different habitats for 119,000–385,000 years can successfully interbreed.

Larval fish sensitivity to a simulated cold-water pulse varies between species and age

The release of cold-water from hypolimnetic zones of impoundments sharply reduces downstream riverine water temperature. This cold-water pollution (CWP) can extend for hundreds of kilometres, severely challenging the physiological ability of aquatic fauna, particularly ectotherms such as fish, to maintain essential processes such as metabolism, development and growth and survival. The impact of CWP on native fish, especially early life stages, is poorly known. We investigated the effect of a 24-hour exposure to a range of environmentally-related water temperatures (8, 10, 12, 14, 16, 18 and 20°C) on three age-classes (&lt;24-hour-old, 7-day and 14-day-old larvae) of two Australian native fish species: Murray cod (Maccullochella peelii) and Macquarie perch (Macquaria australasica). Overall, larvae of M. peelii were more sensitive to lower water temperatures and hence CWP than M. australasica, indicated by higher rates of equilibrium loss. Larvae of M. peelii were most sensitive to exposure at seven days old whereas M. australasica larvae were most sensitive at &lt;24-h-old. Using our results, we modelled pre- and post-impoundment temperature scenarios and estimated the downstream CWP footprint for both species in an Australian river reach. Larvae of M. peelii were predicted to be absent from the first 26 km of river downstream of the impoundment compared with no impact on the distribution of M. australasica. Managing riverine water temperature below impoundments is fundamental to promoting positive outcomes for endemic fish on not only a local, but global basis. This study emphasises the differential impact of CWP among the critical early life stages and fish species and highlights the urgent need to better manage hypolimnetic water releases to improve downstream river ecosystems.

Experimental increases in detritus boost abundances of small‐bodied fish in a sand‐affected stream

Abstract Restoration projects often rely on the assumption that a local intervention will restore diminished populations, without fully understanding the constraints that limit the target species in the first place. In rivers, one common restoration technique is to place large structures, such as wood and boulders, on the bed, with the assumption that fish will subsequently arrive and use them. Nonetheless, providing large habitat structure may not overcome demographic or resource constraints on fish populations, and thus may not aid recovery. We aimed to test if resource constraints (food and cover) are limiting local densities of fishes in a degraded stream by experimentally alleviating these constraints. If the abundance of one or more species is constrained by resource availability, then local numbers of these species should increase following an increase in resources. To test our prediction, we increased the availability of food and microhabitat complexity (cover) at sites in Hughes Creek, a degraded stream in south‐east Australia that has extensive accumulations of sand and limited in‐stream structure. At treatment sites, we hammered pairs of wooden stakes (25 cm apart) into the stream bed so that the ends of stakes protruded just above the water surface at moderate flows. Stakes effectively trapped passing sticks and leaves, which increased local detrital densities and, subsequently, invertebrate densities, hence providing food and cover for fish. Over the course of a year, we compared the changes in fish abundances at treatment sites to unmanipulated control sites. Fish responded quickly to enhanced retention of detritus, with assemblage differences observed between treatment and control sites. We caught more river blackfish (Gadopsis marmoratus), southern pygmy perch (Nannoperca australis), Macquarie perch (Macquaria australasica), and mountain galaxias (Galaxias olidus) at treatment sites on some occasions, indicating that these species may be subject to resource constraints in this stream. The magnitude of observed positive fish responses was influenced by the life‐stage of individuals and local stream conditions. Importantly, treatment effects varied through time and were no longer observed after a large flood affected the study stream. Our results show that resource constraints limit local species abundances and demonstrate a novel method of overcoming these constraints in a small, degraded stream. This is a necessary first step but future work is needed to examine whether increases in abundance are due to the provided resources increasing growth rates, survivorship, or reproduction. This work also highlights the importance of understanding species’ life histories, the broader landscape setting, and the disturbance regime when undertaking site scale restoration.

Differential impacts of a wildfire and post-fire sedimentation event on platypus and fish populations in a Victorian upland river

Context Wildfire can affect freshwater ecosystems in many ways, notably when post-fire rainfall washes ash and sediment into waterways. Aims We investigated species-specific effects of bushfire and subsequent channel sedimentation on the abundance of platypus and fish populations in the upper Buffalo River, Australia. Methods Pre- and post-fire population surveys were conducted using fyke nets. Key results There was no evidence that fish numbers declined because of direct fire effects. However, native two-spined blackfish and Macquarie perch numbers dropped dramatically following post-fire sedimentation, whereas non-native redfin perch increased, most likely as a result of migration from a nearby lake. Platypus captures were consistently recorded at all survey sites both before and after the fire and sediment inflows occurred, with many juveniles being recorded in the first post-fire breeding season. Conclusions The platypus’s greater resilience to post-fire sediment inflows than that of native fish presumably reflects its reliance on lungs rather than gills and its ability to take refuge in burrows. It also has a broad diet, flexible foraging behaviour, is highly vagile and typically stores enough fat to support fasting for up to 2–3 weeks. Implications Management of fire-affected aquatic ecosystems must consider species-specific responses of freshwater vertebrates to fire.

Labile sex chromosomes in the Australian freshwater fish family Percichthyidae.

Sex-specific ecology has management implications, but rapid sex-chromosome turnover in fishes hinders sex-marker development for monomorphic species. We used annotated genomes and reduced-representation sequencing data for two Australian percichthyids, Macquarie perch Macquaria australasica and golden perch M.ambigua, and whole genome resequencing for 50Macquarie perch of each sex, to identify sex-linked loci and develop an affordable sexing assay. In silico pool-seq tests of 1,492,004Macquarie perch SNPs revealed that a 275-kb scaffold was enriched for gametologous loci. Within this scaffold, 22loci were sex-linked in a predominantly XY system, with females being homozygous for the X-linked allele at all 22, and males having the Y-linked allele at >7. Seven XY-gametologous loci (all males, but no females, are heterozygous or homozygous for the male-specific allele) were within a 146-bp region. A PCR-RFLP sexing assay targeting one Y-linked SNP, tested in 66known-sex Macquarie perch and two of each sex of three confamilial species, plus amplicon sequencing of 400bp encompassing the 146-bp region, revealed that the few sex-linked positions differ between species and between Macquarie perch populations. This indicates sex-chromosome lability in Percichthyidae, supported by nonhomologous scaffolds containing sex-linked loci for Macquarie- and golden perches. The present resources facilitate genomic research in Percichthyidae, including formulation of hypotheses about candidate genes of interest such as transcription factor SOX1b that occurs in the 275-kb scaffold ~38kb downstream of the 146-bp region containing seven XY-gametologous loci. Sex-linked markers will be useful for determining genetic sex in some populations and studying sex chromosome turnover.

The value of quantitative environmental DNA analyses for the management of invasive and endangered native fish

Abstract Environmental DNA (eDNA) monitoring is a useful tool for species detection but its use in addressing management questions remains scarce. One factor limiting the use of eDNA as a routine monitoring tool is uncertainty around the potential of eDNA data to estimate species abundance. While several confounding factors limit the ability of eDNA data to estimate absolute abundances at large spatial and temporal scales, eDNA data have the potential to estimate relative species abundances patterns at smaller scales, and this information can assist management. Environmental DNA and conventional monitoring surveys were conducted in the Abercrombie River catchment (Australia) where an incursion of the invasive redfin perch (Perca fluviatulis) threatens the survival of a population of endangered Macquarie perch (Macquaria australasica). Species‐specific assays were used to quantify eDNA concentrations from water samples and estimate the relative abundance of both species. Electrofishing and fyke netting surveys were used to validate key observations from the eDNA survey. Environmental DNA of both species was detected at all sites except one, where redfin perch DNA was not detected. Between species comparisons of eDNA concentrations revealed a clear negative relationship between the eDNA concentrations of both species, consistent with other evidence of redfin perch having a negative impact on Macquarie perch populations. Between site comparisons of redfin perch eDNA concentrations showed evidence of a novel incursion of the species in the upper reaches of the Abercrombie River and conventional monitoring in the following year confirmed the pattern of increased redfin perch abundances from downstream to upstream sites. Relative comparisons of eDNA concentrations of aquatic species can be used to assess species interactions and reveal unexpected species abundance patterns (e.g. allowing inferences of novel incursions of invasive species). This information is critical to evaluate current, and design future, management strategies. Consequently, while deriving absolute species abundances from quantitative eDNA data may remain challenging, the use of quantitative eDNA surveys can provide relative abundance patterns valuable to the conservation and management of invasive and endangered species. The quantitative nature of eDNA survey data has been debated extensively in the current literature because of potential confounding influences. Current study results show that these confounding influences may be less problematic at small spatial scales and quantitative eDNA data can be effective to monitor relative species abundances patterns.

Using multiple sources during reintroduction of a locally extinct population benefits survival and reproduction of an endangered freshwater fish.

Through using different sources, population reintroductions can create genetically diverse populations at low risk of harmful inbreeding and well equipped for adaptation to future environments. Genetic variation from one source can mask locally nonoptimal alleles from another, thereby enhancing adaptive potential and population persistence. We assessed the outcomes in survival, growth and reproduction of using two differentiated sources (genetically diverse Yarra and moderately diverse Dartmouth) for translocations and stocking to reintroduce the endangered Australian freshwater Macquarie perch Macquaria australasica into the Ovens River. For stocking, same‐ and different‐population parents (“cross‐types”) were used during hatchery production. Genetic samples and data on individual fish were collected over three years of monitoring the Ovens. We genetically assigned Ovens fish to their broodstock parents and tested whether cross‐type and genetic dissimilarity between parents are associated with offspring survival, and whether cross‐type and parental dissimilarity or individual genetic diversity are associated with somatic growth rates of stocked fish. We genetically identified translocated fish and assessed local recruit ancestry. Of 296 Ovens fish, 31.1% were inferred to be stocked, 1.3% translocated and 67.6% locally born. Cross‐type strongly predicted survival of stocked offspring: those with two Yarra parents had the highest survival, followed by offspring with two‐population, then Dartmouth, ancestry. Of the Ovens recruits, 59.5% had Yarra, 33.5% two‐population and 7.0% Dartmouth ancestry, despite 67% of stocked and 98% of translocated fish originating from Dartmouth. Offspring with two Yarra parents grew faster than offspring of Dartmouth or two‐population ancestry. Although Dartmouth fish appear to be less fit in the Ovens compared to Yarra fish, possibly due to deleterious variation or genetic or plastic maladaptation, they contribute to the reintroduced population through local interbreeding with Yarra fish and relatively high survival of stocked offspring of two‐population ancestry. Thus, combining compatible stocks is likely to benefit restoration of other wildlife populations.

Dataset for the genome annotation of golden perch and macquarie perch

Dataset for the genome annotation of golden perch and macquarie perch

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.

Comparison of traditional and environmental DNA survey methods for detecting rare and abundant freshwater fish

Abstract Detecting rare species is often a necessity for conservation and management, yet challenging for many field survey methods. Environmental DNA (eDNA) is a highly promising solution that has been shown to outperform many established survey methods. Macquarie perch (Macquaria australasica) is an endangered native species that has declined significantly in range and abundance. Detection of M. australasica was compared with an abundant alien fish species (Oncorhynchus mykiss) using eDNA and three conventional survey methods: gill nets, electrofishing and fyke nets. eDNA occupancy estimates for both fish species were compared using four different models to investigate what effect these differences have on false positives and false negatives for the rare and common fish species. These models used unadjusted eDNA detections in water samples, eDNA detections that have been screened using a limit of detection method to remove potential false positives, eDNA data supplemented with a second survey method, or eDNA data augmented with sequencing of positive polymerase chain reaction replicates. eDNA surveying as a single detection method was found to be more efficient and sensitive compared with each capture method separately and combined. Occupancy estimates for the common and rare species did not vary significantly between the four site occupancy‐detection models, suggesting that supplementary data may not have as much effect on occupancy estimates compared with other approaches such as temporal or spatial sampling. We conclude that eDNA outperforms the three established survey methods for both a rare and common freshwater fish species. Although there was no significant effect of augmenting eDNA survey methods with other survey data, additional data may improve confidence in detection, and provide confirmatory evidence for unexpected or new detections of a species.

Next-generation sequencing of the mitochondrial genome of Macculochella peeli (Percichthyoidei: Percichthyidae)

The Maccullochella peeli belongs to family Maccullochella, and is distributed in Australia and South America (mainly Argentina and Chile). In this paper, the complete mitochondrial genome of M. peeli was determined using next-generation sequencing. The whole mitogenome is a typical circular DNA molecule of 16,442 bp and contains 13 protein-coding genes, 22 transfer RNA genes, 2 ribosomal RNA genes, and a D-loop region, with the base composition of A 31.6%, G 14.3%, T 26.3%, and C 27.8%. Phylogenetic analysis showed that M. peeli was the nearest sister to Macquaria australasica. Our whole mitogenome presented here would be useful for further study of M. peeli.

Climate variability regulates population dynamics of a threatened freshwater fish

Most predictions for the future climate in temperate ecosystems show longer periods of drought followed by more extreme precipitation events. These changes in flow regimes can strongly affect riverine fish populations; therefore, assessing the recovery of populations following these episodic events provides important information to help guide species management. This study investigated the dynamics of 5 spatially distinct riverine populations of the nationally endangered Macquarie perch Macquaria australasica in southeastern Australia from 2007-2018, a period that included the tail end of a decadal long drought followed by extreme fluctuations in river flow. Modelling catch rates and size trends, we found that 4 of the 5 populations showed some synchrony and underwent a slow recovery that was undetectable for several years. The largest increases in population size were driven by the survival of new recruits. Despite this general trend, we could only find a weak association between annual flow extremes and annual population change. This suggests intermediate variations in river flows may have a negligible influence on annual population change or are idiosyncratic in their effect within each waterway or on different life stages. The one population which did not follow this trend occurred in the largest waterway and was subject to legal recreational fishing, suggesting the magnitude of impacts of disturbance on populations occupying larger systems are reduced, and/or that recreational fishing hinders recovery rates following episodic disturbance events such as drought. Our results suggest that forecasting and management of long-lived freshwater fish must incorporate multi-year planning to include factors such as the maintenance of refuges, connectivity and increased protection of mature fish to aid recovery.

The South American and Australian percichthyids and perciliids. What is new about them?

ABSTRACT A study including morphological characters and mitogenomics of South American and Australian fishes previously assigned to Percichthyidae was conducted. Results generated from these different data sets reveal major disagreements concerning the content and interpretation of the so-called percichthyids. A phylogenetic analysis based on 54 morphological characters suggests the existence of two major clades: (1) Percichthyidae, including the South American Percichthys and the Australian taxa Macquaria australasica, Macquaria (= Plectroplites), and Maccullochella; (2) Perciliidae with the South American genus Percilia at the base plus more advanced Australian genera Nannoperca, Nannatherina, Bostockia, and Gadopsis. In contrast, molecular and mitogenomic evidence suggests only one clade (Percichthyidae), with the exclusion of species of Macquaria (= Percalates). Additionally, the results reveal the existence of various taxonomic problems, such as the current interpretation of only one species of Percichthys in Argentina, an interpretation that is not supported by the present study; the existence of cryptic species of Percilia as well as of Gadopsis, Nannoperca, and Macquaria that will increase the diversity of the genera; and the need for an extensive revision of species previously assigned to Percalates versus Macquaria. Disagreements point to the need to develop further research on the so-called percichthyids and perciliids.

Spawning-stock characteristics and migration of a lake-bound population of the endangered Macquarie perch Macquaria australasica.

The intrapopulation variability in the size and age structure of the spawning stock and migration of the threatened Macquarie perch Macquaria australasica in Lake Dartmouth was investigated between 2008 and 2016. Sampling centred on the core reproductive period (October-December) when mature fish migrate from the lake into riverine habitat to spawn. Spawning fish were predominantly large, spanning a broad age structure, with a high proportion of fish (25%) aged 15-30 years. The overall median size of spawning fish did not change for males or females during the 9 year study period. The size of the smaller mature male fish did change in some years suggesting a small proportion of male M. australasica matured at age 1+ and 2+. Acoustic telemetry employed over 3 years showed that M. australasica were most likely to be in the spawning reach from October to mid-December, migrated to this reach annually and moved large distances throughout the lake all year, with no evidence for any spatial structuring. Mature fish sometimes occupied the spawning reach for several months after the core reproductive period, which increased their vulnerability to recreational fishing. Males tagged in the lake were seldom recorded in the spawning reach, presumably because a high proportion had not yet entered the spawning stock despite their size suggesting maturity. Maintaining a broad age and size-structure of the spawning stock of long-lived iteroparous fish species is crucial for recruitment stability and population persistence. Overexploitation of the spawning stock has probably contributed to previous population declines in the lake as well as the collapse of other M. australasica populations in south-eastern Australia.

Regional‐scale extremes in river discharge and localised spawning stock abundance influence recruitment dynamics of a threatened freshwater fish

AbstractHighly variable recruitment is common for many riverine fish species, governed by a wide range of biotic and abiotic drivers that operate at local and regional scales. The dynamics and drivers of recruitment for many Australian freshwater fish species, particularly those that are rare and long‐lived, are relatively undescribed. This study describes the recruitment dynamics of an endangered riverine fish, Macquarie perch Macquaria australasica, across 5 isolated populations from southeastern Australia, and relates these dynamics to drivers that vary at local and regional scales. We hypothesised large flow events occurring during the core egg, and larval period would be negatively associated with recruitment strength and that recruitment patterns across populations would fluctuate in synchrony in response to extremes in river discharge resulting from regional‐scale climatic patterns.Discharge during the core egg and larval period, which was highly correlated across the region, and a local‐scale variable, spawning stock abundance, were the covariates most important in explaining recruitment strength. We also observed synchronised patterns in recruitment across our populations, thus conforming to predictions of the Moran effect (environmental synchrony). The findings suggest that most remnant populations of Macquarie perch, which are now predominantly isolated within small tributary systems characterised by highly variable flows, face a heightened risk of poor recruitment periods, particularly under climate change predictions. The synchronised patterns in recruitment suggest that threatened freshwater fishes such as Macquarie perch with highly fragmented isolated populations have an increased risk of the regional population becoming imperilled, thus the need for a coordinated multijurisdictional conservation approach.