Leiopotherapon Unicolor Research Articles

Evaluation and refinement of a fish movement model for a tropical Australian stream subject to mine contaminant egress

The impacts of mine contaminants on ecological connectivity in rivers and streams are poorly documented globally. We used acoustic telemetry to evaluate and refine conceptual models of fish movement in Magela Creek, a stream in the wet-dry tropics of Australia. This creek receives wastewater discharge from a nearby uranium mine, and a secondary objective was to describe behavioural responses of fish to one such discharge event. Of 55 fish (black bream Hephaestus fuliginosus, saratoga Scleropages jardinii, sharp-nose grunter Syncomistes butleri) tagged in dry season refuge pools 18 km upstream of the mine lease area (RPA [Ranger Project Area]), 16 (29%) moved downstream after the first wet season flows, using the RPA as habitat for 3–5 months before moving upstream to their previous locations as flows receded. Of 39 fish (spangled perch Leiopotherapon unicolor, barred grunter Amniataba percoides, black catfish Neosilurus ater) tagged ~ 8–12 km downstream of the RPA in the late wet season, only two were subsequently detected in the RPA. Direct and camera-based observations of 12 species of upstream-migrating fish during mine-water discharge in the late wet season showed no evidence of mine-water avoidance. Our results demonstrate that Magela Creek provides wet season habitat for fish within the RPA and acts as a migration pathway that connects lowland reaches and floodplains to upstream dry season refuges. Use by fish of waterbodies within the RPA highlights the need to manage the site to ensure that future contaminant egress and water quality do not adversely affect fish migration and habitat suitability.

Neophobic behavioural responses of parasitised fish to a potential predator and baited hook

Many juvenile fish show essential avoidance of predators but are also faced with the need to show risky asset-acquiring behaviour, such as trying new food sources, many of which are known to be influenced by parasite infection. Here, we investigated the links between parasite infection, anti-predator behaviour and neophobia towards a novel food presented on a baited hook in fish. Juvenile Spangled perch (Leipotherapon unicolor) undertook two behavioural tests in our laboratory, before being dissected and examined for external and internal parasites. We used an adapted conditioned place avoidance (CPA) paradigm to examine responses to a predator fish and in a separate test, we examined neophobia of a baited hook. Of the 69 Spangled perch studied, 27% of fish were uninfected and at least one of nematodes, Protozoa/Myxozoa or Monogenea were found in the remaining fish. Fish spent less time in the side of the tank where the predator was previously encountered, than before encounters, indicating that fish can learn to avoid locations where predators were previously observed. We found that fish spent longer in the side of the tank where the predator was visible than in the same side of the tank in earlier trials without the predator, supporting previous studies showing that fish actively approach and engage in predator inspection. Fish infected with Protozoa/Myxozoa and camallanid nematodes were less likely to enter the side of the tank with the predator than uninfected fish, suggesting a reluctance to approach a predator in these infected fish. However, Protozoa/Myxozoa and camallanid infected fish bit the baited hook sooner than uninfected fish, possibly indicating less neophobia of the baited hook in fish with these infections. Avoiding to approach a predator yet reduced neophobia to novel foods in some infected fish suggest that parasites do not exert a general, overall, effect on risk aversiveness. Instead, changes in neophobic behaviour appear complex and we discuss the possibility that parasite-induced changes in fish behaviour may be modulated by altered hunger levels and reduced locomotion brought about by illness.

Chronic exposure to a pervasive pharmaceutical pollutant erodes among-individual phenotypic variation in a fish

Pharmaceutical pollution is now recognised as a major emerging agent of global change. Increasingly, pharmaceutical pollutants are documented to disrupt ecologically important physiological and behavioural traits in exposed wildlife. However, little is known about potential impacts of pharmaceutical exposure on among-individual variation in these traits, despite phenotypic diversity being critical for population resilience to environmental change. Furthermore, although wildlife commonly experience multiple stressors contemporaneously, potential interactive effects between pharmaceuticals and biological stressors—such as predation threat—remain poorly understood. To redress this, we investigated the impacts of long-term exposure to the pervasive pharmaceutical pollutant fluoxetine (Prozac®) on among-individual variation in metabolic and behavioural traits, and the combined impacts of fluoxetine exposure and predation threat on mean metabolic and behavioural traits in a freshwater fish, the guppy (Poecilia reticulata). Using a mesocosm system, guppy populations were exposed for 15 months to one of two field-realistic levels of fluoxetine (nominal concentrations: 30 and 300 ng/L) or a solvent control. Fish from these populations were then tested for metabolic rate (oxygen uptake) and behaviour (activity), both before and after experiencing one of three levels of a predation treatment: an empty tank, a non-predatory fish (Melanotaenia splendida) or a predatory fish (Leiopotherapon unicolor). Guppies from both fluoxetine treatments had ∼70% lower among-individual variation in their activity levels, compared to unexposed fish. Similarly, fluoxetine exposure at the higher dosage was associated with a significant (26%) reduction in individual-level variation in oxygen uptake relative to unexposed fish. In addition, mean baseline metabolic rate was disrupted in low-fluoxetine exposed fish, although mean metabolic and behavioural responses to predation threat were not affected. Overall, our study demonstrates that long-term exposure to a pervasive pharmaceutical pollutant alters ecologically relevant traits in fish and erodes among-individual variability, which may be detrimental to the stability of contaminated populations globally.

Simultaneous exposure to nitrate and low pH reduces the blood oxygen-carrying capacity and functional performance of a freshwater fish.

Human activities present aquatic species with numerous of environmental challenges, including excessive nutrient pollution (nitrate) and altered pH regimes (freshwater acidification). In isolation, elevated nitrate and acidic pH can lower the blood oxygen-carrying capacity of aquatic species and cause corresponding declines in key functional performance traits such as growth and locomotor capacity. These factors may pose considerable physiological challenges to organisms but little is known about their combined effects. To characterise the energetic and physiological consequences of simultaneous exposure to nitrate and low pH, we exposed spangled perch (Leiopotherapon unicolor) to a combination of nitrate (0, 50 or 100 mg L−1) and pH (pH 7.0 or 4.0) treatments in a factorial experimental design. Blood oxygen-carrying capacity (haemoglobin concentration, methaemoglobin concentrations and oxygen equilibrium curves), aerobic scope and functional performance traits (growth, swimming performance and post-exercise recovery) were assessed after 28 days of exposure. The oxygen-carrying capacity of fish exposed to elevated nitrate (50 and 100 mg L−1) was compromised due to reductions in haematocrit, functional haemoglobin levels and a 3-fold increase in methaemoglobin concentrations. Oxygen uptake was also impeded due to a right shift in oxygen–haemoglobin binding curves of fish exposed to nitrate and pH 4.0 simultaneously. A reduced blood oxygen-carrying capacity translated to a lowered aerobic scope, and the functional performance of fish (growth and swimming performance and increased post-exercise recovery times) was compromised by the combined effects of nitrate and low pH. These results highlight the impacts on aquatic organisms living in environments threatened by excessive nitrate and acidic pH conditions.

Complete mitogenomes of five ecologically diverse Australian freshwater fishes

Complete mitochondrial genome sequences were determined for five species of Australian freshwater fishes, representing a diverse range of ecologies and life histories. Mitogenomes were sequenced and annotated for Craterocephalus stramineus (Atherinidae); Hypseleotris klunzingeri (Eleotridae); Lovettia sealii (Galaxiidae); Leiopotherapon unicolor (Terapontidae) and Nematalosa erebi (Clupeidae). The five new mitogenomes each share the typical vertebrate mitochondrial arrangement of 13 protein coding genes, 22 tRNA genes, two rRNA genes and a control region. These sequences will be a useful resource for studies of evolutionary relationships and for management applications.

The pharmaceutical pollutant fluoxetine alters reproductive behaviour in a fish independent of predation risk

Pharmaceutical pollutants constitute a major threat to wildlife because of their capacity to induce biological effects at low doses. One such pollutant is the antidepressant fluoxetine, which has been detected in surface waters globally at levels that recent studies suggest can alter physiology and behaviour in aquatic organisms. However, wildlife exposed to pharmaceutical contaminants are typically confronted with multiple stressors simultaneously, including predation risk, which is a particularly important natural stressor that can have direct (e.g. mortality) and indirect (e.g. changed prey behaviour) fitness effects. Accordingly, we investigated potential impacts of environmentally realistic fluoxetine exposure on reproductive behaviour in the guppy (Poecilia reticulata) under predation risk. Specifically, we tested whether fluoxetine exposure altered mating behaviour in male and female guppies in the presence of either a predatory spangled perch (Leiopotherapon unicolor) or a non-predatory rainbowfish (Melanotaenia splendida) control. We found that fluoxetine and the presence of a predatory spangled perch did not interact to affect reproductive behaviour. We also found that, independent of a predatory threat, fluoxetine exposure altered male mating strategy, with males in the high treatment conducting significantly more coercive ‘sneak’ copulations, whereas the number of courtship displays performed was not significantly affected. Moreover, while fluoxetine exposure did not significantly affect the amount of time that males and females spent following one another, we found that females, but not males, followed a potential partner less when in the presence of the predatory fish. Finally, both sexes reacted to the risk of predation by spending less time in close proximity to a predator than a non-predator. In combination, our findings highlight the capacity of fluoxetine to influence processes of sexual selection at field-realistic concentrations and emphasise the importance of considering multiple stressors when assessing impacts of pharmaceutical pollutants on the behaviour of wildlife.

Genome-Wide SNPs Identify Limits to Connectivity in the Extreme Freshwater Disperser, Spangled Perch Leiopotherapon unicolor (Terapontidae).

The utility of restriction-site associated DNA sequencing (RADseq) to resolve fine-scale population structure was tested on an abundant and vagile fish species in a tropical river. Australia's most widespread freshwater fish, the "extreme disperser" Leiopotherapon unicolor was sampled from 6 locations in an unregulated system, the Daly River in Australia's Northern Territory. Despite an expectation of high connectivity based on life history knowledge of this species derived from arid zone habitats, L. unicolor was not a panmictic population in the tropical lower Daly. Using ~14000 polymorphic RADseq loci, we found a pattern of upstream versus downstream population subdivision and evidence for differentiation among tributary populations. The magnitude of population structure was low with narrow confidence intervals (global FST = 0.014; 95% CI = 0.012-0.016). Confidence intervals around pairwise FST estimates were all nonzero and consistent with the results of clustering analyses. This population structure was not explained by spatially heterogeneous selection acting on a subset of loci, or by sampling groups of closely related individuals (average within-site relatedness ≈ 0). One implication of the low but significant structure observed in the tropics is the possibility that L. unicolor may exhibit contrasting patterns of migratory biology in tropical versus arid zone habitats. We conclude that the RADseq revolution holds promise for delineating subtle patterns of population subdivision in species characterized by high within-population variation and low among-population differentiation.

Fish assemblage dynamics in an intermittent river of the northern Australian wet–dry tropics

AbstractIntermittent rivers make up a large portion of the global river network and are the dominant river type in northern Australia. Increased pressure is being placed on such systems, and a better understanding of their ecology is needed. We examined, over a 7‐year period, the fish fauna of the intermittent Fergusson River, a major tributary of the Daly River of the northern Australia. Changes in habitat structure with the onset of the dry season involved contraction of the riffle/run/pool habitat to a single refugial pool, the size of which was determined by antecedent wet season hydrology. The fishes present comprised a subset of species present within the Daly River main channel and consisted of the most widely distributed of northern Australia's freshwater fishes. The Fergusson River provides suitable spawning habitat for species during the wet season (e.g. Hephaestus fuliginosus, Leiopotherapon unicolor and Neosilurus catfishes) and during the dry season for a different set of species (e.g. Amniataba percoides, Melanotaenia australis and Glossogobius aureus). Little year‐to‐year variation in assemblage structure was observed early in the dry season, whereas interannual variation in late dry season assemblages was substantial. Dry season recruitment imparted some of the interannual variability in assemblage structure recorded between late dry season samples. Piscivorous fishes were an important, but temporally variable, component of the assemblage present in the late dry season refugial habitat, and predation was potentially another important source of variation in assemblage structure.

Contrasting and complex evolutionary histories within the terapontid grunter genus Hephaestus revealed by nuclear and mitochondrial genes

Contrasting evolutionary histories may be revealed by mitochondrial and nuclear information. Divergent New Guinean and eastern and western Australian lineages of Hephaestus fuliginosus (sooty grunter) were detected using mitochondrial data, with the extent of divergence consistent with cryptic speciation events. However, this phylogeographic pattern was not supported by nuclear gene data, and evidence for cryptic speciation appears driven almost entirely by introgression between H. fuliginosus and congeners on the periphery of its distribution (e.g. with H. tulliensis, H. jenkinsi or H. roemeri). Hephaestus fuliginosus is a single species with a complex evolutionary history. Introgression on the eastern coast is consistent with transfer of the mitochondrial genome of the resident species (H. tulliensis) to the invading species (H. fuliginosus) and may have provided the metabolic capacity for H. fuliginosus to spread into the cooler rainforest environment of the Wet Tropics region. Mitochondrial and nuclear analyses both identified the genus Hephaestus as polyphyletic with H. carbo and H. habbemai placed in a clade with Leiopotherapon unicolor and Amniataba percoides. The present study demonstrated the need to consider a variety of genetic information when assessing species identity in a widespread species and the need for a systematic revision of the genus and family as a whole.

Spangled perch (Leiopotherapon unicolor) in the southern Murray‐Darling Basin: Flood dispersal and short‐term persistence outside its core range

AbstractThe spangled perch Leiopotherapon unicolor is considered a rare vagrant in the southern Murray‐Darling Basin, Australia, due to its intolerance of the relatively cool water temperatures that prevail during winter months. This study details 1342 records of the species from 68 locations between 2010 and 2014 outside its accepted ‘core adult range’ following widespread flooding during 2010 and 2011. Although records of the species declined over 2013, L. unicolor remained resident in the southern Murray‐Darling Basin as of April 2014. The species persisted in several locations for three consecutive winters with recruitment documented at two sites. This study represents the first identification of the dispersal of large numbers of L. unicolor into the southern Murray‐Darling Basin, persistence beyond a single winter, and recruitment by the species in habitats south of its recognized ‘core adult range’. Targeted research would determine the potential for predicted environmental changes (artificially warmer drainage wetlands, climate change and greater floodplain connectivity) to facilitate longer term persistence and range expansion by the species in the southern Murray‐Darling Basin.

DNA barcoding of freshwater fishes and the development of a quantitative qPCR assay for the species-specific detection and quantification of fish larvae from plankton samples.

The barcoding of mitochondrial cytochrome c oxidase subunit 1 (coI) gene was amplified and sequenced from 16 species of freshwater fishes found in Lake Wivenhoe (south-eastern Queensland, Australia) to support monitoring of reservoir fish populations, ecosystem function and water health. In this study, 630-650 bp sequences of the coI barcoding gene from 100 specimens representing 15 genera, 13 families and two subclasses of fishes allowed 14 of the 16 species to be identified and differentiated. The mean ± s.e. Kimura 2 parameter divergence within and between species was 0.52 ± 0.10 and 23.8 ± 2.20% respectively, indicating that barcodes can be used to discriminate most of the fish species accurately. The two terapontids, Amniataba percoides and Leiopotherapon unicolor, however, shared coI DNA sequences and could not be differentiated using this gene. A barcoding database was established and a qPCR assay was developed using coI sequences to identify and quantify proportional abundances of fish species in ichthyoplankton samples from Lake Wivenhoe. These methods provide a viable alternative to the time-consuming process of manually enumerating and identifying ichthyoplankton samples.

A recent predatory encounter influences male courtship in a desert-dwelling fish

Increased predation risk is one of the greatest costs associated with sexual signaling. Studies have shown that individuals often adjust their signaling behavior in the presence of predators with consequences for current reproductive opportunities. Predation risk, however, can vary over time and is rarely (if ever) constant. Despite this, surprisingly little is known about how recent exposure to a predator might influence an individual’s subsequent signaling behavior. Here, we set out to determine how a previous encounter with a piscivorous predator affected courtship behavior in a freshwater fish, the desert goby, Chlamydogobius eremius. We tested male courtship before and after manipulating their perception of risk. We found that male gobies previously exposed to a predatory fish, the spangled perch, Leiopotherapon unicolor, took longer to initiate courtship and subsequently spent less time courting females. Such males, instead, spent more time taking refuge in their nests. In contrast, unexposed control male gobies and males that were exposed to a nonpredatory fish, the Lake Eyre Hardyhead, Craterocephalus eyresii, did not alter their courtship behavior. Our results suggest that male courtship behavior is not only sensitive to the immediate presence of a predator but can persist even after the predatory threat has abated.

Fish diet composition in floodplain lagoons of an Australian dryland river in relation to an extended dry period following flooding

Floodplain rivers worldwide are threatened by loss of connectivity to their floodplains and hence reduced benefits from floodplain energy subsidies. Dryland rivers with ‘boom and bust’ ecological responses to flooding and extended dry periods may be particularly vulnerable. This paper describes variations in dietary composition of three fish species of contrasting trophic position in dryland floodplain lagoons with variable flood inundation and drying histories. The study species were Ambassis agassizii - a microphagic carnivore, Leiopotherapon unicolor - a carnivore/omnivore, and Nematalosa erebi - an algivore/detritivor. Despite the range of food items recorded in fish guts, each species fed mostly on relatively few food categories and few food items within each category. Most of the spatial (i.e. among lagoons) and temporal dietary variation was associated with different proportional contributions of these food items. Given the absence or low magnitude of flooding during the study period, temporal changes in diets of the three species are probably the result of successional changes in composition of invertebrate prey as the dry season progressed. The focus of each fish species on relatively few food categories and a few reliable food items within each category may be the most profitable foraging strategy when food resources are limiting in progressively drying floodplain lagoons.

Emergence of Epizootic Ulcerative Syndrome in Native Fish of the Murray-Darling River System, Australia: Hosts, Distribution and Possible Vectors

Epizootic ulcerative syndrome (EUS) is a fish disease of international significance and reportable to the Office International des Epizootics. In June 2010, bony herring Nematalosa erebi, golden perch Macquaria ambigua, Murray cod Maccullochella peelii and spangled perch Leiopotherapon unicolor with severe ulcers were sampled from the Murray-Darling River System (MDRS) between Bourke and Brewarrina, New South Wales Australia. Histopathology and polymerase chain reaction identified the fungus-like oomycete Aphanomyces invadans, the causative agent of EUS. Apart from one previous record in N. erebi, EUS has been recorded in the wild only from coastal drainages in Australia. This study is the first published account of A. invadans in the wild fish populations of the MDRS, and is the first confirmed record of EUS in M. ambigua, M. peelii and L. unicolor. Ulcerated carp Cyprinus carpio collected at the time of the same epizootic were not found to be infected by EUS, supporting previous accounts of resistance against the disease by this species. The lack of previous clinical evidence, the large number of new hosts (n = 3), the geographic extent (200 km) of this epizootic, the severity of ulceration and apparent high pathogenicity suggest a relatively recent invasion by A. invadans. The epizootic and associated environmental factors are documented and discussed within the context of possible vectors for its entry into the MDRS and recommendations regarding continued surveillance, research and biosecurity are made.

Allochthonous and autochthonous carbon sources for fish in floodplain lagoons of an Australian dryland river

Dryland rivers associated with arid and semi-arid land areas offer an opportunity to explore food web concepts and models of energy sources in systems that experience unpredictable flooding and long dry spells. This study investigated the sources of energy supporting three species of fish feeding at different trophic levels within floodplain lagoons of the Macintyre River in the headwaters of the Murray-Darling river system, Australia. Stable isotope analyses revealed that fish consumers derived, on average, 46.9% of their biomass from zooplankton, 38.1% from Coarse Particulate Organic Matter (CPOM) and 24.0% from algae. Ambassis agassizii derived on average 57.6% of its biomass carbon from zooplankton and 20.4–27.8% from algae or CPOM. Leiopotherapon unicolor derived most of its carbon from zooplankton and CPOM (38.3–39.5%), with relatively high contributions from algae compared to the other species (33.3%). An average of 48.4% of the biomass of Nematalosa erebi was derived from zooplankton, with CPOM contributing another 38.1%. Zooplankton was the most important source of organic carbon supporting all three fish species in floodplain lagoons. Phytoplankton, and possibly, particulate organic matter in the seston, are the most likely energy sources for the planktonic suspension feeders (zooplankton) and, consequently, the fish that feed on them. These results indicate a stronger dependence of consumers on autochthonous sources and on locally produced organic matter from the riparian zone (i.e., the Riverine Productivity Model), than on other resources.

Fishes of the King Edward River in the Kimberley region, Western Australia

The King Edward River, in the far north of the Kimberley region of Western Australia drains approximately 10,000 km2 and discharges into the Timor Sea near the town of Kalumburu. This study represents an ichthyological survey of the river’s freshwaters and revealed that the number of freshwater fishes of the King Edward River is higher than has previously been recorded for a Western Australian river. Twenty-six strictly freshwater fish species were recorded, which is three species higher than the much larger Fitzroy River in the southern Kimberley. The study also identified a number of range extensions, including Butler’s Grunter and Shovel-nosed Catfish to the west, and the Slender Gudgeon to the north and east. A possibly undescribed species of glassfish, that differs morphologically from described species in arrangement of head spines, fin rays, as well as relative body measurements, is reported. A considerable proportion of Jenkins’ Grunter, which is widespread throughout the system but essentially restricted to main channel sites, had ‘blubber-lips’. There were significant differences in the prevailing fish fauna of the different reaches of the King Edward River system. Thus fish associations in the upper King Edward River main channel were significantly different to those in the tributaries and the main channel of the Carson River. Similarly, the fauna of the Carson River, which was much more diverse than the King Edward River main channel and tributary sites, was characterised by many species that were not found in other parts of the river. The presence of natural barriers, such as waterfalls or rock bars do not permit upstream migrations of fishes and are considered to be the main factor in limiting the distribution of some species. For example, many species are restricted to the lower sections of the Carson River, and include Bony Bream, Lesser Salmon Catfish, Shovel-nosed Catfish, Black Catfish, False-spined Catfish, Freshwater Longtom, Prince Regent Hardyhead, Mouth Almighty, Barred Grunter and Butler’s Grunter. It is hypothesised that these natural barriers were in place long before many of these latter species colonised the King Edward River. Some species tend to only be found within tributary sites, e.g. Kimberley Mogurnda, while others are most abundant in tributaries rather than main channel sites, e.g. Western Rainbowfish and Spangled Perch. Waterfalls are also seen as limiting the number of migratory marine/estuarine species that enter freshwaters. For example, only three species that require the marine/estuarine environment to complete their life-cycle were captured in the freshwaters of the King Edward River system. This compares to 14 species that utilise the freshwaters of the Fitzroy River.

The importance of zooplankton in the diets of three native fish species in floodplain waterholes of a dryland river, the Macintyre River, Australia

The zooplankton of freshwater systems has been recognized as an important energy resource for fish of small body size that, in turn, provide energy to piscivorous fish consumers higher up the food web. This study evaluates the importance of zooplankton to the diets of three species of fish living in floodplain waterholes of an Australian dryland river. The species selected for study represent different trophic categories in waterhole food webs: Ambassis agassizii is a microcarnivore, Leiopotherapon unicolor is an omnivore, and Nematalosa erebi is a detritivore. Dietary differences among size classes of each species were also evaluated to understand possible ontogenetic shifts in zooplankton consumption. Ambassis agassizii fed primarily on zooplankton (99.9%, made up mostly of 81.6% Calanoida and 17.4% Moinidae), regardless of the size of individual fish. Leiopotherapon unicolor fed on zooplankton (47%, mostly Daphniidae and Moinidae) and aquatic insects (46.7%). Smaller individuals of Leiopotherapon unicolor (30–49 mm TL—total length) were responsible for 36.1% of the plankton consumed by the species. Nematalosa erebi fed on detritus (84.6%) with zooplankton (Calanoida, Moinidae, and Cyclopoida) contributing only 13.7% of the mean diet. Smaller individuals (40–69 mm TL) were responsible for 98% of the plankton consumed by Nematalosa erebi, and individuals of 40–49 mm (TL) fed exclusively on zooplankton (53.8% Moinidae and 46.2% Calanoida). Although the three fish species had different diets, reflecting differences in species-specific and ontogenetic morphological and behavioral characteristics, zooplankton formed the basis of the diet of all species when young. These results confirm the importance of zooplankton as a major food resource for three fish species and smaller size classes of these species in floodplain waterholes of the Macintyre River, Australia.

Dead fish and frogs associated with Cane Toads near Darwin

Discusses the interactions between Cane Toads and fish near Darwin. Many Spangled Perch Leiopotherapon unicolor were found floating dead on the surface of the lagoon where thousands of Cane Toad tadpoles and toadlets were observed, however it is still not certain that consuming Cane Toads kill fish.

The molecular systematics of Leiopotherapon unicolor (Günther, 1859): testing for cryptic speciation in Australia's most widespread freshwater fish

Leiopotherapon unicolor is the most widespread freshwater fish species in Australia. A comprehensive allozyme and mitochondrial DNA 16S rRNA data set was assembled from 141 specimens of L. unicolor collected Australia-wide in order to test for cryptic speciation in this far-ranging species. Surprisingly, little genetic diversity was observed within L. unicolor and provided no evidence for the existence of cryptic species within this lineage. In contrast, a small sample set of L. aheneus used as the outgroup showed two highly divergent haplotypes strongly suggestive of cryptic speciation. L. unicolor has a number of ecological and life history attributes that may explain the lack of significant genetic divergence over substantial geographical distances. The occurrence of other widespread fish and crustacean species that also display only limited genetic diversity indicate that climate conditions more favourable to dispersal across central and northern Australia than is suggested by the extent of present-day aridity have occurred in the relatively recent geological past.

The fishes of Lake Kununurra, a highly regulated section of the Ord River in northern Western Australia

The Ord River, situated in the east Kimberley region of Western Australia, is regulated by two darns that supply irrigation water for tropical agriculture. The regulation of water in the 55 km span of river between these dams has resulted in this section now resembling a lacustrine rather than riverine environment that is reflected in its name, Lake Kununurra. Utilising various sampling techniques we captured/observed 4157 fish from 19 species in 13 families, whilst the presence of a further three species was confirmed by reliable sources. Nematalosa erebi, Craterocephalus stramineus and Melanotaenia austrahs were the three most widespread and abundant species, being encountered throughout the lake and representing -66% of all fish recorded. Ambassis sp., Arius midgleyi, A. graeHei, Glossamia aprion, Amniataba percoides, Hephaestus jenkinsi, Glossogobius giurus and Toxotes chatareus were found throughout the lake but generally at fewer sites and in smaller numbers (-30% of all fish) than the three dominant species. The remaining species Neosilurus ater, Strongylura kreHtii, Leiopotherapon unicolor, Syncomistes but/eri, Lates calcari{er, Mogumda mogumda, Oxyeleotris lineolatus and Ambassis madeayi were generally found at few sites and in low numbers, and accounted for less than 4% of the overall catch. The regulation of the Ord River has apparently altered the species composition and abundances in Lake Kununurra. For example, marine/estuarine species, commonly encountered in the freshwaters of large northern Australian Rivers, are largely absent, while species such as L. unicolor, which is one of the most abundant species in nearby rivers and tropical Australian rivers in general, contributed to <1°/,) of the total catch.