Nannoperca Research Articles

Range-wide fragmentation in a threatened fish associated with post-European settlement modification in the Murray–Darling Basin, Australia

Distinguishing the relative influence of historic (i.e. natural) versus anthropogenic factors in metapopulation structure is an important but often overlooked step in management programs of threatened species. Biotas in freshwater wetlands and floodplains, such as those in the Murray–Darling Basin (MDB)—one of Australia’s most impacted ecosystems, are particularly susceptible to anthropogenic fragmentation. Here we present a comprehensive multilocus assessment of genetic variation in the threatened southern pygmy perch Nannoperca australis (578 individuals; 45 localities; microsatellite, allozyme and mitochondrial DNA datasets), an ecological specialist with low dispersal potential. We assess patterns of spatial structure and genetic diversity in populations spanning the highly fragmented MDB and test whether recent anthropogenic modification has disrupted range-wide connectivity. We detected strong and hierarchical population structure, very low genetic diversity and lack of contemporary gene flow across the MDB. In contrast, the apparent absence of pronounced or long-term phylogeographic structure suggests that observed population divergences generally do not reflect deeply historic natural fragmentation. Coalescent-based analyses supported this inference, revealing that divergence times between populations from the upper and lower MDB fall into the period of European settlement. It appears that the observed contemporary isolation of populations is partly explained by the severe modification of the MDB post-dating the onset of European settlement. Our integrated approach substantially improves the interpretation of how fragmentation impacts present-day biodiversity. It also provides novel contributions for risk-assessing management actions in the context of captive breeding and translocations of small freshwater fishes, a group of increasing global conservation concern.

Susceptibility of a number of Australian freshwater fishes to dwarf gourami iridovirus (Infectious spleen and kidney necrosis virus).

Megalocytiviruses cause high mortality diseases that have seriously impacted aquaculture, with the most frequent outbreaks occurring in East and South-East Asia. The international trade of juvenile fish for food and ornamental aquaculture has aided the spread of these viruses, which have spread to Europe and Australia and other regions. Australian freshwater fishes were examined for susceptibility to infection with the exotic megalocytivirus, dwarf gourami iridovirus (DGIV), which belongs to a group with the type species, Infectious spleen and kidney necrosis virus (ISKNV). Fish were held at 23±1°C and challenged by intraperitoneal (IP) injection or by cohabitation with Murray cod, Maccullochella peelii (Mitchell) infected with DGIV. A species was deemed to be susceptible to DGIV based on evidence of viral replication, as determined by qPCR, and megalocytic inclusion bodies observed histologically. Horizontal transmission occurred between infected Murray cod and golden perch, Macquaria ambigua (Richardson), Macquarie perch, Macquaria australasica (Cuvier) and Murray cod. This indicated that DGIV shed from infected fish held at 23°C can survive in fresh water and subsequently infect these naïve fish. Further, DGIV administered IP was highly pathogenic to golden perch, Macquarie perch and Murray cod. Compared to these species, the susceptibility of southern pygmy perch, Nannoperca australis (Gunther) was lower. Freshwater catfish (dewfish), Tandanus tandanus (Mitchell), were not susceptible under the experimental conditions based on the absence of clinical disease, mortality and virus replication. This study showed the potential risks associated with naïve and DGIV-infected fish sharing a common water source.

A novel holistic framework for genetic‐based captive‐breeding and reintroduction programs

Research in reintroduction biology has provided a greater understanding of the often limited success of species reintroductions and highlighted the need for scientifically rigorous approaches in reintroduction programs. We examined the recent genetic-based captive-breeding and reintroduction literature to showcase the underuse of the genetic data gathered. We devised a framework that takes full advantage of the genetic data through assessment of the genetic makeup of populations before (past component of the framework), during (present component), and after (future component) captive-breeding and reintroduction events to understand their conservation potential and maximize their success. We empirically applied our framework to two small fishes: Yarra pygmy perch (Nannoperca obscura) and southern pygmy perch (Nannoperca australis). Each of these species has a locally adapted and geographically isolated lineage that is endemic to the highly threatened lower Murray-Darling Basin in Australia. These two populations were rescued during Australia's recent decade-long Millennium Drought, when their persistence became entirely dependent on captive-breeding and subsequent reintroduction efforts. Using historical demographic analyses, we found differences and similarities between the species in the genetic impacts of past natural and anthropogenic events that occurred in situ, such as European settlement (past component). Subsequently, successful maintenance of genetic diversity in captivity-despite skewed brooder contribution to offspring-was achieved through carefully managed genetic-based breeding (present component). Finally, genetic monitoring revealed the survival and recruitment of released captive-bred offspring in the wild (future component). Our holistic framework often requires no additional data collection to that typically gathered in genetic-based breeding programs, is applicable to a wide range of species, advances the genetic considerations of reintroduction programs, and is expected to improve with the use of next-generation sequencing technology.

Effect of salinity on growth of juvenile Yarra pygmy perch (Nannoperca obscura: Percichthyidae)

The threatened Yarra pygmy perch (Nannoperca obscura) is an obligate freshwater fish endemic to the south-eastern coast of mainland Australia, where a majority of river systems have been heavily modified since European settlement. The purpose of this garden study was to explore any relationship between the growth rate of juvenile N. obscura with respect to salinity. Trials were conducted encompassing perceived and potential ranges within the species’ environment, through five salinity treatments and recorded growth after 8 weeks. Two brood-groups were trialed simultaneously to observe any intrapopulation variance in phenotypic response potentially linked to genetic variance. The salinity trials found a clear model indicating increasing growth for moderate salinities (i.e. 2.5–7.5 ppt), therefore identifying the ideal salinity range for N. obscura juveniles. Phenotypic response between brood-groups was varied and inconsistent, potentially reflecting low genetic variability. With a limited genetic variance restricting adaptability, tolerance to a changing environment would be reduced. Therefore increased salinization and subsequent flushing events within habitats may be key threats to the species’ survival.

Mapping and quantifying groundwater inflows to Deep Creek (Maribyrnong catchment, SE Australia) using 222Rn, implications for protecting groundwater-dependant ecosystems

Understanding groundwater inflows to rivers is important in managing connected groundwater and surface water systems and for protecting groundwater-dependant ecosystems. This study defines the distribution of gaining reaches and estimates groundwater inflows to a 62 km long section of Deep Creek (Maribyrnong catchment, Australia) using 222Rn. During summer months, Deep Creek ceases to flow and comprises a chain of ponds that δ18O and δ2H values, major ion concentrations, and 222Rn activities imply are groundwater fed. During the period where the river flows, the relative contribution of groundwater inflows to total river discharge ranges from ∼14% at high flow conditions to ∼100% at low flows. That the predicted groundwater inflows account for all of the increase in discharge at low flow conditions lends confidence to the mass balance calculations. Near-continuous 27 week 222Rn monitoring at one location in the middle of the catchment confirms the inverse correlation between river discharge and relative groundwater inflows, and also implies that there are limited bank return flows. Variations in groundwater inflows are related to geology and topography. High groundwater inflows occur where the river is at the edge of its floodplain, adjacent to hills composed of basement rocks, or flowing through steep incised valleys. Understanding the distribution of groundwater inflows and quantifying the contribution of groundwater to Deep Creek is important for managing and protecting the surface water resources, which support the endangered Yarra pygmy perch.

Catchment-Scale Conservation Units Identified for the Threatened Yarra Pygmy Perch (Nannoperca obscura) in Highly Modified River Systems

Habitat fragmentation caused by human activities alters metapopulation dynamics and decreases biological connectivity through reduced migration and gene flow, leading to lowered levels of population genetic diversity and to local extinctions. The threatened Yarra pygmy perch, Nannoperca obscura, is a poor disperser found in small, isolated populations in wetlands and streams of southeastern Australia. Modifications to natural flow regimes in anthropogenically-impacted river systems have recently reduced the amount of habitat for this species and likely further limited its opportunity to disperse. We employed highly resolving microsatellite DNA markers to assess genetic variation, population structure and the spatial scale that dispersal takes place across the distribution of this freshwater fish and used this information to identify conservation units for management. The levels of genetic variation found for N. obscura are amongst the lowest reported for a fish species (mean heterozygosity of 0.318 and mean allelic richness of 1.92). We identified very strong population genetic structure, nil to little evidence of recent migration among demes and a minimum of 11 units for conservation management, hierarchically nested within four major genetic lineages. A combination of spatial analytical methods revealed hierarchical genetic structure corresponding with catchment boundaries and also demonstrated significant isolation by riverine distance. Our findings have implications for the national recovery plan of this species by demonstrating that N. obscura populations should be managed at a catchment level and highlighting the need to restore habitat and avoid further alteration of the natural hydrology.

Intraspecific variation in the growth and survival of juvenile fish exposed to Eucalyptus leachate

Whilst changes in freshwater assemblages along gradients of environmental stress have been relatively well studied, we know far less about intraspecific variation to these same stressors. A stressor common in fresh waters worldwide is leachates from terrestrial plants. Leachates alter the physiochemical environment of fresh waters by lowering pH and dissolved oxygen and also releasing toxic compounds such as polyphenols and tannins, all of which can be detrimental to aquatic organisms. We investigated how chronic exposure to Eucalyptus leaf leachate affected the growth and survival of juvenile southern pygmy perch (Nannoperca australis) collected from three populations with different litter inputs, hydrology and observed leachate concentrations. Chronic exposure to elevated leachate levels negatively impacted growth and survival, but the magnitude of these lethal and sublethal responses was conditional on body size and source population. Bigger fish had increased survival at high leachate levels but overall slower growth rates. Body size also varied among populations and fish from the population exposed to the lowest natural leachate concentrations had the highest average stress tolerance. Significant intraspecific variation in both growth and survival caused by Eucalyptus leachate exposure indicates that the magnitude (but not direction) of these stress responses varies across the landscape. This raises the potential for leachate-induced selection to operate at an among-population scale. The importance of body size demonstrates that the timing of leachate exposure during ontogeny is central in determining the magnitude of biological response, with early life stages being most vulnerable. Overall, we demonstrate that Eucalyptus leachates are prevalent and potent selective agents that can trigger important sublethal impacts, beyond those associated with more familiar fish kills, and reiterate that dissolved organic carbon is more than just an energy source in aquatic environments.

Dispersal and recruitment of fish in an intermittent stream network

Animal movement is an important process connecting habitats in heterogeneous landscapes, and can play a key role in population persistence. Laboratory swim trials were conducted to determine and compare the dispersal capabilities of two native Australian fish, mountain galaxias (Galaxias olidus, Family Galaxiidae) and southern pygmy perch (Nannoperca australis, Family Nannopercidae) that maintain populations in hydrologically variable and intermittently flowing streams in south-eastern Australia. These experiments showed that G. olidus had significantly greater swimming endurance under a range of flow velocities. Concurrent field surveys were used to establish whether swimming abilities observed in laboratory studies were consistent with patterns of inferred movement from distribution and abundance patterns observed in the field. Data collected at multiple sites from headwater to lowland reaches along multiple streams revealed substantial temporal changes in the distribution of young-of-year (0+) G. olidus, with spawning occurring at upland sites in winter, followed by downstream larval migration and subsequent upstream movement in late spring. Observed spatial and temporal patterns in G. olidus abundances were consistent with a source-sink population structure, which may be disrupted by prolonged cease-to-flow periods during drought years. In contrast, results for N. australis suggested limited dispersal, with restricted local populations that persist at sites with permanent surface water. These field and laboratory findings complement our understanding of the spatial population structure of these two species in intermittent streams, and highlight the importance of understanding the role of dispersal in species conservation and habitat restoration.

Nannoperca pygmaea, a new species of pygmy perch (Teleostei: Percichthyidae) from Western Australia.

A new species of pygmy perch (Percichthyidae) from south-western Australia is described on the basis of 15 specimens collected from the Hay River system. Nannoperca pygmaea sp. nov. differs from the sympatric congener N. vittata (Castelnau) by the absence of dark pigment on the ventral surface anterior to the anus, the possession of thin latero-ventral stripes, generally fewer dorsal rays and fewer anal rays, hind margin of scales on caudal peduncle without distinct pigment, and a more pronounced spot (ocellus) that is surrounded by a halo at the termination of the caudal peduncle. The new species is distinguished from congeners Nannoperca australis Günther, N. oxleyana Whitley and N. variegata Kuiter and Allen in possessing an exposed and serrated preorbital bone and jaws that may just reach to below the anterior margin of the eye, versus a smooth and hidden preorbital and the jaws reaching to at least below the pupil; and from the remaining congener, N. obscura (Klunzinger) in possessing a distinct haloed ocellus at base of caudal fin versus an indistinct barring, as well as a dark spot behind operculum, and the lack of dusky scale margins. It differs from the other sympatric pygmy perch found in the region, N. balstoni Regan, by the presence of an exposed rear edge of the preorbital (vs. hidden under skin), fewer transverse scale rows (13 vs. 15-16), small mouth (rarely reaching eye vs. reaching well beyond eye), ctenoid (vs. cycloid) body scales, generally fewer pectoral rays and smaller maximum size. Allozyme analyses unequivocally demonstrate that sympatric populations of N. pygmaea sp. nov. and N. vittata belong in different genetic lineages, display no genetic intermediates, and are diagnosable by fixed allozyme differences at 15 different loci. Due to its extremely restricted range, where it is known from only 0.06 km2, N. pygmaea sp. nov. requires urgent legislative protection.

The role of continental shelf width in determining freshwater phylogeographic patterns in south‐eastern Australian pygmy perches (Teleostei: Percichthyidae)

Biogeographic patterns displayed by obligate freshwater organisms are intimately related to the nature and extent of connectivity between suitable habitats. Two of the more significant barriers to freshwater connections are seawater and major drainage divides. South-eastern Australia provides a contrast between these barriers as it has discrete areas that are likely influenced to a greater or lesser extent by each barrier type. We use continental shelf width as a proxy for the potential degree of river coalescence during low sea levels. Our specific hypothesis is that the degree of phylogeographic divergence between coastal river basins should correspond to the continental shelf width of each region. This predicts that genetic divergences between river basins should be lowest in regions with a wider continental shelf and that regions with similar continental shelf width should have similar genetic divergences. Pygmy perches (Nannoperca australis and Nannoperca 'flindersi') in south-eastern Australia provide an ideal opportunity to test these biogeographic hypotheses. Phylogeographic patterns were examined based on range-wide sampling of 82 populations for cytochrome b and 23 polymorphic allozyme loci. Our results recovered only limited support for our continental shelf width hypothesis, although patterns within Bass clade were largely congruent with reconstructed low sea-level drainage patterns. In addition, we identified several instances of drainage divide crossings, typically associated with low elevational differences. Our results demonstrate high levels of genetic heterogeneity with important conservation implications, especially for declining populations in the Murray-Darling Basin and a highly restricted disjunct population in Ansons River, Tasmania.

Let’s not forget the small fishes – conservation of two threatened species of pygmy perch in south-eastern Australia

Small species without commercial value are often overlooked in conservation management. Pygmy perches are minature percichthyid fishes from temperate southern Australia of significant conservation concern, with five of the seven described species being threatened nationally. The present paper examines the plight of Yarra pygmy perch Nannoperca obscura, and variegated pygmy perch N. variegata, and discusses the progress of national (and State) recovery-plan actions. Threats and risks to these species are considerable; however, overall, few recovery actions have been completed and the status of many populations is unknown following the recent ‘millenium drought’. Habitat restoration, fish rescues, environmental water delivery and research into distribution, ecology and population dynamics are largely driven by individuals within singular local management authorities. Like many small fishes, they receive less attention than do larger ones and a cross-jurisdictional national recovery team is required to prioritise, coordinate and implement conservation efforts before the continued persistence of these species can be assured. These two small fishes are representative of many similar species and the lessons from the present case study may be applied elsewhere throughout the world.

Conservation biology and management of the endangered Oxleyan pygmy perch Nannoperca oxleyana in Australia

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 17:169-178 (2012) - DOI: https://doi.org/10.3354/esr00414 Theme Section: Endangered river fish: threats and conservation options Conservation biology and management of the endangered Oxleyan pygmy perch Nannoperca oxleyana in Australia James T. Knight1,*, Angela H. Arthington2, Gabrielle S. Holder1, R. Bill Talbot1 1NSW Department of Trade and Investment, Regional Infrastructure and Services, Port Stephens Fisheries Institute, Nelson Bay, New South Wales 2315, Australia 2Australian Rivers Institute and DIVERSITAS, Griffith University, Nathan, Queensland 4111, Australia *Email: james.knight@industry.nsw.gov.au ABSTRACT: The global biodiversity crisis particularly affects freshwater fishes. Currently, 20% of Australia’s highly endemic freshwater fishes are formally recognised as being of conservation concern under national, state and territory listings. Four of the 5 described species of Nannoperca (Percichthyidae) are threatened with extinction, with N. oxleyana Whitley listed as endangered under Australian legislation and internationally by the IUCN. National recovery planning has commenced with the objective of returning this species to a position of ‘viability in nature’ in New South Wales (NSW) and Queensland. This paper describes the conservation biology of N. oxleyana, providing a case history for a small species of no commercial importance threatened by the classical triumvirate of habitat degradation and loss; small, declining and fluctuating populations driven more by environmental conditions than demographic forces; and the effects of introduced species. A process for declaring critical habitat for N. oxleyana has commenced in NSW. Habitat protection involves managing threats, including run-off originating from unsealed roads, herbicide use, fire management activities and disturbance by recreational users such as 4-wheel drivers and campers. Information on the distribution and breeding patterns of N. oxleyana has been provided to local and state government authorities to assist in managing drainage and development schemes that might impact N. oxleyana habitat. Monitoring has confirmed the persistence of many N. oxleyana populations in both jurisdictions. KEY WORDS: Endangered fishes · Conservation biology · Threat analysis · Recovery planning Full text in pdf format PreviousNextCite this article as: Knight JT, Arthington AH, Holder GS, Talbot RB (2012) Conservation biology and management of the endangered Oxleyan pygmy perch Nannoperca oxleyana in Australia. Endang Species Res 17:169-178. https://doi.org/10.3354/esr00414 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 17, No. 2. Online publication date: May 23, 2012 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2012 Inter-Research.

Spatial variation in egg size and egg number reflects trade‐offs and bet‐hedging in a freshwater fish

1. Maternal reproductive investment is thought to reflect a trade-off between offspring size and fecundity, and models generally predict that mothers inhabiting adverse environments will produce fewer, larger offspring. More recently, the importance of environmental unpredictability in influencing maternal investment has been considered, with some models predicting that mothers should adopt a diversified bet-hedging strategy whilst others a conservative bet-hedging strategy. 2. We explore spatial egg size and fecundity patterns in the freshwater fish southern pygmy perch (Nannoperca australis) that inhabits a diversity of streams along gradients of environmental quality, variability and predictability. 3. Contrary to some predictions, N.australis populations inhabiting increasingly harsh streams produced more numerous and smaller eggs. Furthermore, within-female egg size variability increased as environments became more unpredictable. 4. We argue that in harsh environments or those prone to physical disturbance, sources of mortality are size independent with offspring size having only a minor influence on offspring fitness. Instead, maternal fitness is maximized by producing many small eggs, increasing the likelihood that some offspring will disperse to permanent water. We also provide empirical support for diversified bet-hedging as an adaptive strategy when future environmental quality is uncertain and suggest egg size may be a more appropriate fitness measure in stable environments characterized by size-dependent fitness. These results likely reflect spatial patterns of adaptive plasticity and bet-hedging in response to both predictable and unpredictable environmental variance and highlight the importance of considering both trait averages and variance. 5. Reproductive life-history traits can vary predictably along environmental gradients. Human activity, such as the hydrological modification of natural flow regimes, alters the form and magnitude of these gradients, and this can have both ecological and evolutionary implications for biota adapted to now non-existent natural environmental heterogeneity.

Isolation and PCR-multiplex genotyping of 18 novel microsatellite markers for the threatened southern pygmy perch (Nannoperca australis)

A set of 18 microsatellites was developed for the freshwater fish southern pygmy perch (SPP) Nannoperca australis (Percichthyidae). SPP is an endangered species endemic to South-eastern Australia. Applying a next generation DNA sequencing approach, we obtained 12,725 sequences containing putative microsatellite motifs using 1/8 of a shot-gun pyrosequencing reaction. Twenty-three microsatellite motifs with enough flanking sequence were selected for primer design. All 18 microsatellite loci were successfully genotyped using three multiplex reactions in 38 specimens of SPP rescued from the wild and kept in captivity. The number of alleles per locus varied from 3 to 15 alleles per locus (mean = 7.6) and the observed heterozygosity ranged from 0.368 to 0.921 (mean = 0.648). Evidence for null alleles was observed only for one locus (Nau33). No deviation from Hardy–Weinberg equilibrium or linkage disequilibrium between pairs of loci were detected. These polymorphic markers will prove useful for an ongoing conservation-breeding program of SPP aimed at minimizing kinship in captivity and for studies on landscape and restoration genetics.

A Phylogenetic Analysis of Pygmy Perches (Teleostei: Percichthyidae) with an Assessment of the Major Historical Influences on Aquatic Biogeography in Southern Australia

The biogeography of southern Australia is characterized by a repeated pattern of relatedness between the biota of southwestern and southeastern Australia. Both areas possess a temperate climate but are separated by a vast arid region, currently lacking permanent freshwater habitats, which has become increasingly drier since about 15 Ma. Aquatic organisms have thus potentially remained isolated for a considerable time. Pygmy perches (Nannatherina and Nannoperca, Percichthyidae) provide an excellent scenario for investigating biogeographic relationships between southwestern and southeastern regions as multiple species occur on either side of Australia. This allows us to potentially differentiate between "Multiple Invasion" and "Endemic Speciation," the two major hypotheses proposed to account for current distributions. The first suggests that multiple east-west movements have occurred, whereas the second suggests a single east-west split, with current biodiversity in each region being reciprocally monophyletic. Systematic relationships within this group were investigated with the mitochondrial cytochrome b gene; nuclear intron and exon sequences from S7, RAG1, and RAG2; and 53 allozyme loci. Our data supported the hypothesis of multiple movements across southern Australia based on a consistent lack of support for reciprocal monophyly of eastern and western species. This study appears to be the first example of an animal group displaying clear multiple east-west movement in southern Australia, as all other aquatic and terrestrial fauna previously examined displayed a single east-west split. Despite a high degree of sympatry within each region, the only evidence for hybridization was found between Nannoperca australis and N. obscura, with the latter having its mitochondrial genome completely replaced by that of N. australis, with no evidence for nuclear introgression. This is one of only a few confirmed examples of complete replacement of the mitochondrial genome in one species with that of another. Cryptic differentiation was also evident within the two most widespread species, N. australis and N. vittata, indicating that these likely consist of multiple species. We also highlight the need for multiple molecular markers with different strengths in order to obtain a more robust phylogeny, despite problems resulting from potential incongruences between data sets.

Eucalyptus leachate inhibits reproduction in a freshwater fish

Summary 1. Dissolved organic carbon (DOC) can induce lethal and sub-lethal effects in exposed biota via hypoxic blackwater events and the toxicity of leached compounds. Little is known of how DOC exposure affects fish reproduction despite the fact that its release can coincide with spawning-associated flow pulses. 2. River red gum (Eucalyptus camaldulensis) leaf leachate is a major source of DOC in Australian freshwaters and includes the toxic plant secondary metabolites polyphenols and tannins. High concentrations of leachate are released when leaves on floodplains or dry stream channels are inundated by water. 3. Southern pygmy perch (Nannoperca australis) from naturally high and naturally low Eucalyptus leachate environments in south-east Australia were exposed to elevated leachate levels to investigate the effects of DOC on reproduction and to explore whether response patterns were consistent with populations becoming locally adapted to historical leachate levels. 4. Fish exposed to leachate were half as likely to reach sexual maturity as control fish. Fish from a naturally high-exposure population tended to reach sexual maturity earlier than those from a naturally low-exposure population. Leachate exposure had no effect on either egg size or fecundity. 5. Our results suggest that leachate-exposed mothers did not reproduce because they were physiologically stressed or perceive the environment to be unsuitable, which raises the potential of plastic or adaptive responses to this stressor. The negative sub-lethal effects observed have important fitness implications for individuals, the viability of populations and the management of environmental flows and riparian zones.

Development of 21 microsatellite markers for the threatened Yarra pygmy perch (Nannoperca obscura) through 454 shot-gun pyrosequencing

Using a next generation sequencing approach, a set of 21 new microsatellites loci was developed from the threatened freshwater fish Yarra pygmy perch (YPP) Nannoperca obscura (Percichthyidae). All markers were successfully genotyped using 28 YPP kept in captivity. These animals represent an entire population rescued from the lower Murray-Darling Basin in Australia before its habitat dried out. As expected due to the critical conservation status of the population, we observed low genetic variation across most loci (mean number of alleles per locus = 2.76; mean heterozygosity = 0.28). No deviations from Hardy–Weinberg equilibrium or linkage disequilibrium were detected and only one locus (Nob30) showed evidence for null alleles. These molecular markers represent important resources for the ongoing YPP captive breeding program, and for upcoming restoration and landscape genetic studies of this species.

Nuptial coloration varies with ambient light environment in a freshwater fish

Visual signals play a vital role in many animal communication systems. Signal design, however, often varies within species, raising evolutionarily important questions concerning the maintenance of phenotypic diversity. We analysed nuptial colour variation within and among nine populations of southern pygmy perch (Nannoperca australis Günther) along an environmental light gradient. Within populations, larger males were redder and blacker, and better-condition males were blacker. Among populations, red colour was positively correlated with the amount of orange-red light present, suggesting that males are likely optimizing signal conspicuousness by producing proportionally larger and redder patches in broad spectrum environments with more orange-red light. Signal contrast, in this regard, is maximized when red colour, appearing bright because of the prevalence of red wavelengths, is viewed against the water-column background. Together, our results are concordant with the sensory drive hypothesis; selection favours signal adaptations or signal plasticity to ensure communication efficacy is maximized in different light environments.

Phylogeographic structure in the threatened Yarra pygmy perch Nannoperca obscura (Teleostei: Percichthyidae) has major implications for declining populations

Molecular genetic information should be a pre-requisite when evaluating conservation priorities in highly structured species such as freshwater fishes. Nuclear (allozyme) and mitochondrial (cytochrome b) markers were used to investigate phylogeographic structure in the Yarra pygmy perch Nannoperca obscura (Klunzinger), a threatened freshwater fish endemic to mainland south-eastern Australia. Complementary patterns of strong, geographically defined sub-structure were observed including a major east–west divergence (at the Glenelg River), four diagnosable lineages, and statistically-significant differences between most populations. Accordingly, four Evolutionarily Significant Units (ESUs) are defined and multiple, drainage-scale Management Units (MUs) suggested. Since Nannoperca obscura is a relatively poor disperser with no apparent gene flow between most populations, any regional extirpation would see the irreversible loss of genetic diversity. This is problematic, as several populations, most notably a recently discovered ESU in the Murray-Darling Basin, are feared extirpated through a combination of anthropogenic threats and severe drought. The potential loss of unique evolutionarily components within N. obscura soon after their discovery highlights with some urgency, the need to define and protect conservation units in highly modified freshwater habitats.

Unidentified microsporidian in western pygmy perchEdelia vittata(Nannopercidae) from Australia

Specimens of western pygmy perch, Edelia vittata Castelnau 1873, were submitted for examination because of the presence of black masses in the body wall in the abdominal area. The owner reported that approximately 10% of mature fish in one dam were affected. The masses had no apparent effect on the health of affected fish, but they were unsuitable for sale for aesthetic reasons. After necropsy and histological examination, the masses were found to be microsporidial xenomas within the abdominal cavity. Transmission electron microscopy results suggest that this microsporidian is a previously unreported species, because the melanised xenoma wall and internal structure of the spores differ from previously described species. The epidemiology of the parasite remains largely unknown and highlights the need for further surveys of the disease status and parasites of Australian native fish, especially those of interest to aquaculturists.