Galaxiid Fish Research Articles

Isolation management to protect threatened native galaxiid fish species: Lessons from Aotearoa New Zealand

Abstract The use of barriers in freshwater systems to mitigate invasions, known as isolation management, has been increasingly implemented as a protection strategy for native fish. Barriers are crucial for securing vulnerable populations, but much remains to be learnt about the drivers of success and the implications of deliberate fragmentation. In Aotearoa‐New Zealand, henceforth Aotearoa, native non‐migratory galaxiid (NMG) fishes are characterized by a disproportionate number of threatened species with introduced salmonids (trout) identified as a key driver of NMG declines. We conducted a qualitative review of barriers protecting NMG in Aotearoa, illustrating varying outcomes and current knowledge gaps with case studies. Barrier types ranged from natural bedrock waterfalls, shallow velocity chutes and drying reaches to deliberately engineered structures (known commonly as exclusion barriers). Barriers were typically located in headwater streams or spring systems. NMG species secured by fragmentation often have high conservation value and barriers are essential for their protection. Despite the critical role of these barriers, the isolated NMG populations above them are at risk of stochastic extirpation, invasion, or re‐invasion. Exclusion barriers may restrict access to habitat for native migratory fish species and can sometimes alter or remove ideal mesohabitat from protected populations. Overall, when using exclusion barriers, managers must assess extinction risk for individual populations by isolation or invasion, balancing benefits and consequences. However, these assessments are frequently based on incomplete data and hindered by lack of general understanding of the underpinning processes. Despite well‐documented benefits to NMG population survival, key knowledge gaps such as long‐term viability of isolated populations, combinations of physical barrier parameters conferring exclusion under all flow regimes and extent of habitat loss to other native species still exist.

Multi-gene insights into the taxonomy and conservation of Tasmania’s galaxiid fishes

Context Galaxiids are a widespread, southern hemisphere, radiation of mostly obligate freshwater fishes. Tasmania houses a diversity of endemic species of Galaxias and Paragalaxias. Of these, many are at risk of extinction, being landlocked, range-restricted and subject to anthropogenic threats, placing a high-conservation priority on the region. Aim Our aim was to synthesise historic and published molecular datasets to provide the sound systematic framework needed to underpin future conservation and taxonomic efforts for Tasmanian galaxiids. Methods Novel and published nuclear (allozyme) and matrilineal (cytb) datasets were generated and integrated for every putative Tasmanian galaxiid species lacking a comparable multi-gene assessment. Key results The Tasmanian galaxiids are phylogenetically diverse, with molecular data generally supporting the accepted taxonomy, but with potential species-level diversity noted within an alpine radiation of the Galaxias truttaceus complex and further support for synonymy of G. niger within G. brevipinnis. Conclusions This study highlights the value of multi-locus studies in both validating species-level taxonomy and resolving taxonomic ambiguities and conservation priorities within Tasmania’s galaxiids. Implications Our integrated genetic analyses provide a framework to underpin more in-depth genomic approaches to assess additional cryptic diversity and conservation planning, such as genetic rescue and ex situ population security.

Conservation of endangered galaxiid fishes in the Falkland Islands requires urgent action on invasive brown trout

Non-native salmonids are protected in the Southern hemisphere where they sustain aquaculture and lucrative sport fisheries, but also impact many native fishes, which poses a conservation conundrum. Legal protection and human-assisted secondary releases may have helped salmonids to spread, but this has seldom been tested. We reconstructed the introduction of brown trout (Salmo trutta) to the Falkland Islands using historical records and modelled its dispersal and probability of invasion using a generalized linear model and Leave One out Cross Validation. Our results indicate that establishment success was ~ 88%, and that dispersal was facilitated over land by proximity to invaded sites and density of stream-road crossings, suggesting it was human assisted. Brown trout have already invaded 54% of Falkland rivers, which are 2.9–4.5 times less likely to contain native galaxiids than uninvaded streams. Without strong containment we predict brown trout will invade nearly all suitable freshwater habitats in the Falklands within the next ~ 70 years, which might put native freshwater fishes at a high risk of extinction.

Flood disturbance mediates the strength of stream trophic cascades caused by trout

AbstractTrophic cascades are important features of aquatic ecosystems, but much variation in their strength remains unexplained. Disturbance could restrict cascade occurrence by limiting predator distribution, and increase cascade strength by lowering defended herbivore abundance. These possibilities were investigated in 20 New Zealand rivers varying both in flooding disturbance (measured by bed movement) and presence of non‐native predatory trout. Trout were often, but not always, associated with indirectly increasing algal abundance compared to similar rivers with native galaxiid fishes. Floods explained variation in cascades by (1) resetting algal abundance such that algal minima were related to bed movement; (2) preventing occurrence by restricting trout abundance in the most disturbed rivers; and (3) increasing potential cascade strength by removing defended herbivores. These observations indicate strong nonlinear influences of disturbance on both trophic cascade occurrence and maximum strength which will be important to consider as climate change alters disturbance regimes.

SNP analyses and acoustic tagging reveal multiple origins and widespread dispersal of invasive brown trout in the Falkland Islands.

Biological invasions are important causes of biodiversity loss, particularly in remote islands. Brown trout (Salmo trutta) have been widely introduced throughout the Southern Hemisphere, impacting endangered native fauna, particularly galaxiid fishes, through predation and competition. However, due to their importance for sport fishing and aquaculture farming, attempts to curtail the impacts of invasive salmonids have generally been met with limited support and the best prospects for protecting native galaxiids is to predict where and how salmonids might disperse. We analysed 266 invasive brown trout from 14 rivers and ponds across the Falkland Islands as well as 32 trout from three potential source populations, using a panel of 592 single nucleotide polymorphisms (SNPs) and acoustic tagging, to ascertain their origins and current patterns of dispersal. We identified four genetically distinct clusters with high levels of genetic diversity and low admixture, likely reflecting the different origins of the invasive brown trout populations. Our analysis suggests that many trout populations in the Falklands may have originated from one of the donor populations analysed (River Wey). The highest genetic diversity was observed in the rivers with the greatest number of introductions and diverse origins, while the lowest diversity corresponded to a location without documented introductions, likely colonized by natural dispersal. High levels of gene flow indicated widespread migration of brown trout across the Falkland Islands, likely aided by anadromous dispersal. This is supported by data from acoustically tagged fish, three of which were detected frequently moving between two rivers ~26 km apart. Our results suggest that, without containment measures, brown trout may invade the last remaining refuges for the native endangered Aplochiton spp. We provide new insights into the origin and dispersal of invasive brown trout in the Falkland Islands that can pave the way for a targeted approach to limit their impact on native fish fauna.

Evolutionary Genetics and Biogeography of Galaxiid Fishes (Teleostei: Galaxiiformes: Galaxiidae)

Since the dawn of the discipline, biogeographers have wondered at the widespread distribution of galaxiid fishes throughout temperate regions of the Southern Hemisphere [...]

Could spatial heterogeneity in flow disturbance drive temporal stability of native–invasive species co‐occurrence in riverscapes?

Abstract Spatial heterogeneity of abiotic influences like disturbance in riverscapes could play an important role in dispersal‐aided community stability. We tested if higher spatial variability in conditions around river confluences caused by different flood disturbance regimes in branches could possibly influence the stability of a fish assemblage dominated by strong negative interactions between non‐native trout and native galaxiid fishes. We used field surveys to evaluate the effects of disturbance‐driven differences between river branches on fish densities and temporal variation in the relative abundance of galaxiids. Three repeated electrofishing surveys were conducted in two reaches of all branches of eight confluences in Canterbury, New Zealand. We found the differences in flood disturbance regimes between the two stream branches joining at a confluence were associated with higher mean fish abundance and more temporal stability in the relative abundance of native fish. Conversely, when flood disturbance conditions in the two streams joining were similar, resulting in a homogeneous confluence, fish abundance was lower and temporal variability was higher. For homogeneous confluences, strong interactions between native galaxiids and invasive trout probably produced lower fish densities where rivers with low flow disturbance met, whereas when two highly flow‐disturbed rivers met, environmental harshness probably lowered fish densities. By comparison, enhanced galaxiid temporal stability at confluences containing both disturbed and stable river branches probably reflected the combined effects of refugia from trout predation in disturbed branches and refugia from flooding in stable branches. Overall, these results are likely to reflect the combined effects of population‐specific responses to physical heterogeneity and spatially variable interspecific interactions. They may mean that river network configuration, and confluences especially, could influence community stability through a habitat portfolio effect. Furthermore, it will be worth investigating further whether preservation or restoration of differences in flow disturbance conditions in riverscapes encourages higher ecosystem resilience in the face of global change.

A Global Assessment of Parasite Diversity in Galaxiid Fishes

Free-living species often receive greater conservation attention than the parasites they support, with parasite conservation often being hindered by a lack of parasite biodiversity knowledge. This study aimed to determine the current state of knowledge regarding parasites of the Southern Hemisphere freshwater fish family Galaxiidae, in order to identify knowledge gaps to focus future research attention. Specifically, we assessed how galaxiid–parasite knowledge differs among geographic regions in relation to research effort (i.e., number of studies or fish individuals examined, extent of tissue examination, taxonomic resolution), in addition to ecological traits known to influence parasite richness. To date, ~50% of galaxiid species have been examined for parasites, though the majority of studies have focused on single parasite taxa rather than assessing the full diversity of macro- and microparasites. The highest number of parasites were observed from Argentinean galaxiids, and studies in all geographic regions were biased towards the highly abundant and most widely distributed galaxiid species, Galaxias maculatus. Parasite diversity generally increased with the number of studies and individual fish examined, however studies which examined parasites from all body tissues could overcome the effects of low study effort. In order to promote further understanding of galaxiid–parasite biodiversity, we provide a series of recommendations, including the use of molecular techniques to verify parasite identity, and highlight the future roles both fish biologists and parasitologists can play.

A new high‐resolution melt curve eDNA assay to monitor the simultaneous presence of invasive brown trout (Salmo trutta) and endangered galaxiids

AbstractBrown trout are highly invasive in the Southern Hemisphere where they support important sport fisheries and aquaculture activities, which may impact endangered native galaxiid fishes and cause conflicts. To protect native galaxiids it is essential to monitor changes in species distributions, but this can be difficult when species are rare or difficult to sample. We developed and validated, both in the laboratory and in the field, a new assay using a high‐resolution melt curve (HRM)‐eDNA approach to simultaneously detect the presence of two threatened native galaxiids (Aplochiton zebra and Aplochiton taeniatus) and the invasive brown trout (Salmo trutta). Using this method, we found brown trout in 30% of the sampled waterbodies and Aplochiton sp. in 15% of them. Galaxiids were solely identified as being present in rivers that lacked brown trout, with both native species coexisting in two of the three rivers where they were detected, despite their different niche preferences. These assays can be used to monitor threatened zebra trout as well as invasive brown trout populations, allowing conservation managers to target areas for intervention.

Historical and Contemporary Diversity of Galaxiids in South America: Biogeographic and Phylogenetic Perspectives

Galaxiid fishes from South America are represented by three genera (Aplochiton, Brachygalaxias and Galaxias) and eight species. Their genetic patterns have been studied over the last two decades to disentangle how historical and contemporary processes influenced their biogeographic distribution and phylogeographic patterns. Here we review and synthesize this body of work. Phylogeographic approaches reveal the important role played by orogeny and the expansion/melting of glacial ice during the Quaternary. Populations retreated to glacial refugia during glacial times and some systems experienced drainage reversals from the Atlantic to the Pacific following deglaciation. Although most species expanded their populations and increased their genetic diversity during the Holocene, the introduction of salmonids and the construction of dams are likely to lead to a decline in genetic diversity for at least some species. An improvement in our understanding of the processes that influenced historical and contemporary diversity patterns among galaxiid and other native fishes in South America is necessary for addressing the cumulative and synergistic impacts of human activity on this unique freshwater fauna.

River Capture and Freshwater Biological Evolution: A Review of Galaxiid Fish Vicariance

Geological processes can strongly affect the distribution and diversification of freshwater-limited species. In particular, a combination of geological and biological data has suggested that Earth history processes can drive vicariant isolation and speciation in non-migratory freshwater fishes. Here, we synthesise recently published geological and freshwater phylogeographic data to illustrate that changes in river drainage geometry are important drivers of galaxiid diversification, both in New Zealand and elsewhere. Major river capture events have led to the isolation and divergence of unique and geographically-restricted lineages, including taxa that are now of prime conservation concern. The parallel phylogeographic effects of drainage shifts have been verified by observations of concordant patterns in co-distributed species. Broadly, this study highlights the dynamic interplay between physical and biological processes in geologically active settings.

New Insights into the Distribution, Physiology and Life Histories of South American Galaxiid Fishes, and Potential Threats to This Unique Fauna

South American galaxiids occupy both Patagonia and the ichthyogeographic Chilean Province, encompassing glacial Andean deep lakes, shallow plateau lakes, reservoirs, short Pacific rivers and long Atlantic rivers. The total fish fauna includes 29 species, comprising Neotropical fishes (siluriforms and characids), galaxiids, percichthyids, atherinopsids and mugilids, two lamprey species, and several exotic fishes (salmonids, Gambusia spp. and common carp). The family Galaxiidae shares a common ancestry with the Gondwanan temperate fish fauna, played a major role in the post-glacial colonization of Andean lakes and streams, and contributes key species to the food webs. Galaxiid species occupy an enormous latitudinal gradient, show a wide variety of life history patterns and are the southernmost native freshwater fishes of the world. Knowledge of South American galaxiids has improved notably, but new challenges arise due to climate change, biological invasions, damming, aquaculture and contamination. In this changing environment, the future of South American galaxiids should be carefully considered as a legacy of the old Gondwana and a unique attribute of the freshwaters of southern South America.

A New Species of Cryptocotyle (Digenea: Heterophyidae) Infecting Kelp Gull and a Galaxiid Fish in Patagonian Freshwater Environments: Morphological and Molecular Analyses.

Adults of a species of Cryptocotyle were found infecting the intestine of the kelp gull, Larus dominicanus Lichtenstein, 1823, and metacercariae were found in the fins and muscle of the galaxiid fish, Galaxias platei Steindachner, 1898 (local name "puyen grande"), in Nahuel Huapi National Park (Patagonia). Morphometrics and genetic markers of mitochondrial cytochrome oxidase (COI) and ribosomal internal transcribed spacer 1 (ITS1) confirmed that adults and metacercariae were conspecific and represent a new species, Cryptocotyle dominicana n. sp. The only congener known from South America (Cryptocotyle thapari McIntosh, 1953) matures in river otters (Lutra spp. and Pteronura spp.) in Brazil and Bolivia and differs from the new species in the arrangement of the testes, which are located in tandem in the species from otters. Adults of the new species resemble Cryptocotyle lingua (Creplin, 1825) Fischoeder, 1903 from marine environments of the Northern Hemisphere, both species being characterized by having a linguiform body, oblique testes, and vitelline follicles that extend posteriorly to the level of the ventral sucker. Considering the morphological findings that differentiate the new species from other Cryptocotyle, as well as the molecular analysis that shows significant differences from C. lingua, we conclude that these specimens represent a new species, the first of the genus Cryptocotyle to be described from birds in South America.

Behavioural crypsis in a South African galaxiid fish induced by predatory and non-predatory heterospecifics.

This study investigated recognition of, and behavioural responses to, predatory and non-predatory heterospecifics by a small cryptically coloured fish species, Galaxias 'nebula'. Nebula recognised and differentiated between predatory and non-predatory heterospecifics and altered its behaviour facultatively. With both predatory and non-predatory fishes, the proportion of time spent motionless increased, whereas refugia use was affected only by predators and neither heterospecific affected the time spent active. Although nebula appeared to face no conflict, in that their responses to predatory and non-predatory heterospecifics varied in the same direction and differed only in intensity, the presence of both heterospecifics together induced responses midway between those for each heterospecific separately. Non-predatory heterospecifics thus modified nebula's responses towards predators, potentially making time available for other essential activities such as foraging. This modified predator response may aid its survival in an increasingly threatened habitat.

Oxidative stress in the galaxiid fish, Galaxias maculatus, exposed to binary waterborne mixtures of the pro-oxidant cadmium and the anti-oxidant diclofenac

Chemical mixtures represent environmentally-realistic exposures of contaminants to aquatic biota. However, there remains a limited understanding of how toxicant mixtures may impact biological function, relative to their individual components. In the current study, oxidative stress responses of the freshwater galaxiid fish inanga (Galaxias maculatus) were examined following exposure to the pro-oxidant trace metal cadmium (2 or 9 μg L−1), and the anti-oxidant pharmaceutical drug diclofenac (770 μg L−1), individually or in simple binary mixtures. Cadmium exposure in the absence of diclofenac significantly decreased renal catalase activity, increased hepatic catalase activity, decreased renal superoxide dismutase (SOD) and decreased glutathione-S-transferase activity, effects that are suggestive of anti-oxidant defense inhibition and/or generation of increased reactive oxygen species. Diclofenac exposure in the absence of cadmium resulted in a decreased renal lipid peroxidation, consistent with its known anti-oxidant properties. The presence of waterborne diclofenac altered the effects of cadmium on catalase activity in the liver, SOD activity in the gill, and lipid peroxidation in the liver. Co-exposure with cadmium modulated diclofenac effects on lipid peroxidation in the kidney. These data indicate the capacity of each of these toxicants to offset biological effects of the other when both co-occur in urban waters at specific concentrations. This study also demonstrates the complexity of outcomes in contaminant mixtures, even when these stressors are presented as simple binary combinations.

Acute exposure to an environmentally relevant concentration of diclofenac elicits oxidative stress in the culturally important galaxiid fish Galaxias maculatus.

Diclofenac is a nonsteroidal anti-inflammatory drug (NSAID) of growing concern in aquatic environments worldwide; nevertheless, knowledge of its effects on aquatic biota is restricted to a few model species with limited information regarding its mechanisms of impact. In the present study, diclofenac accumulation, its effects on metabolic rate, ionoregulation, and oxidative stress were examined at environmentally relevant (0.17 µg L-1 ) and elevated (763 µg L-1 ) concentrations in a culturally and economically important galaxiid fish, inanga (Galaxias maculatus), from the Southern Hemisphere. This species is among the most widespread freshwater fish in the world but its sensitivity to emerging contaminants is unknown. Following an acute 96-h exposure, bioconcentration of diclofenac was measured in the inanga whole-body, resulting in an estimated bioconcentration factor of 87 for the 0.17-µg L-1 exposure concentration, approaching values where transfer through the food chain should be considered. Lipid peroxidation in the liver was significantly elevated at both 0.17- and 763-µg L-1 exposure concentrations but lipid peroxidation in the kidney and gill decreased after diclofenac exposure. Catalase activity was also elevated in the liver of inanga but activity decreased in the gill. There were no effects of diclofenac on metabolic rate or ion (sodium and calcium) influx rates. These data indicate that toxicologically relevant adverse outcomes and bioconcentration of diclofenac at environmentally relevant levels warrant additional study in this important fish. Environ Toxicol Chem 2018;37:224-235. © 2017 SETAC.

The Tasmanian Lake Shrimps, Paranaspides Smith, 1908 (Crustacea, Syncarida, Anaspidesidae)

The Tasmanian Lake Shrimps of the genus Paranaspides Smith, 1908 (Syncarida: Anaspidesidae) are endemic to lakes on the eastern Central Plateau, Tasmania, namely Great Lake, Shannon Lagoon, Penstock Lagoon, Arthurs Lake and Woods Lake. Prior to the present study, only the type species, P. lacustris Smith, 1908, was recognized. Reconsideration of Paranaspides from throughout its range, however, showed that Paranaspides from Arthurs Lake and Woods Lakes are referrable to a new species, P. williamsi sp. nov. Morphometric differences in the uropodal exopod and maxilliped, and subtle differences in the morphology of the male pleopods 1 and 2, and colour-in-life distinguish the two species. Genetic divergence (p-distance) between the two species exceeds 10% in mitochondrial COI and 3% in 16S. Both species are described and illustrated, and a lectotype fixed for P. lacustris. Although P. lacustris and P. williamsi occur in relatively close proximity, they occupy different drainages. The Great Lake-Shannon Lagoon-Penstock Lagoon system drains to the southeast, and the Arthurs Lake-Woods Lake system to the northeast. The distributions of P. lacustris and P. williamsi precisely parallel those of a cognate pair of galaxiid fishes, Paragalaxias eleotroides and Paragalaxias mesotes. Given the geological history of the Central Plateau and molecular divergence estimates for Paragalaxias, Paranaspides may also have diverged prior to the Pleistocene glaciations. Species of Paranaspides are dependent on their shallow water algal bed habitat, making them highly susceptible to sudden or significant fluctuations in lake water levels as a result of hydroelectric operations. Both species of Paranaspides have small areas of occupancy and are prone to the effects of hydroelectric activities on their lake habitats; under IUCN Red List criteria, their conservation status corresponds to Vulnerable (D2).

Temperature, invaders and patchy habitat interact to limit the distribution of a vulnerable freshwater fish

AbstractInteracting global‐change drivers such as invasive species and climate warming are likely to have major and potentially unexpected influences on aquatic ecosystems. In river networks, modified water temperature combined with patchy physical conditions will likely cause shifts in the amount and distribution of suitable habitat, with influential invasive species further altering habitat availability. We examined how distributions of a thermally sensitive galaxiid fish native to the alpine rivers of New Zealand, Galaxias paucispondylus, were influenced by these drivers using spatially extensive presence–absence electrofishing surveys of 46 sites spread over four subcatchments. A unimodal response to water temperature and an interaction with substratum size meant G. paucispondylus were limited to streams with average summer water temperatures between 10.6 and 13.8 °C and were absent when average substratum sizes were <36 mm, regardless of temperature. In addition, non‐native trout >150 mm long excluded G. paucispondylus, but were only found in streams with average summer water temperatures <10.6 °C. These influences of trout likely strengthened the unimodal temperature response of G. paucispondylus and led to a very small G. paucispondylus realized niche. When predicted temperature increases were applied to catchment models, G. paucispondylus distributions were patchy and variable across subcatchments. Moreover, local physical characteristics of river networks were particularly important because of the non‐linear and interactive influences of temperature and substratum size on the outcome of species interactions. Therefore, substratum sizes, water temperature and a non‐native predator combined to influence the distribution of this thermally sensitive fish, illustrating how the effects of climate warming will likely be strongly context‐dependent and interactive.

Salinity-dependent nickel accumulation and effects on respiration, ion regulation and oxidative stress in the galaxiid fish, Galaxias maculatus

Inanga (Galaxias maculatus) are a euryhaline and amphidromous Southern hemisphere fish species inhabiting waters highly contaminated in trace elements such as nickel (Ni). Ni is known to exert its toxic effects on aquatic biota via three key mechanisms: inhibition of respiration, impaired ion regulation, and stimulation of oxidative stress. Inanga acclimated to freshwater (FW), 50% seawater (SW) or 100% SW were exposed to 0, 150 or 2000 μg Ni L−1, and tissue Ni accumulation, metabolic rate, ion regulation (tissue ions, calcium (Ca) ion influx), and oxidative stress (catalase activity, protein carbonylation) were measured after 96 h. Ni accumulation increased with Ni exposure concentration in gill, gut and remaining body, but not in liver. Only in the gill was Ni accumulation affected by exposure salinity, with lower branchial Ni burdens in 100% and 50% SW inanga, relative to FW fish. There were no Ni-dependent effects on respiration, or Ca influx, and the only Ni-dependent effect on tissue ion content was on gill potassium. Catalase activity and protein carbonylation were affected by Ni, primarily in FW, but only at 150 μg Ni L−1. Salinity therefore offsets the effects of Ni, despite minimal changes in Ni bioavailability. These data suggest only minor effects of Ni in inanga, even at highly elevated environmental Ni concentrations.

Evolution of the Taieri River catchment, East Otago, New Zealand

ABSTRACTThis paper synthesises geological and biological data to develop an evolutionary history for the Taieri River that currently follows a circuitous 200 km course as one of the main drainages in Otago. The ancestral Taieri River drained only coastal hills initiated in the Miocene, and much of what is now the upper Taieri catchment flowed into the ancestral Clutha River. Major river reorientation events occurred in the upper half of the catchment because of rise of antiformal fold mountains in the Pleistocene, forming a new divide between the Taieri and Clutha catchments. Coeval incision of a gorge through a volcanic rock barrier connected the upper catchment to the lower Taieri River. The sparse Pleistocene sedimentary record documents these drainage changes via contrasting distribution of distinctive clasts derived from greywacke mountains on the northern edge of the Otago Schist belt. These major capture events are also supported by distributions and genetic divergences of freshwater galaxiid fish species. Erosion during Pleistocene rise of the antiformal mountains caused recycling of placer gold into Clutha tributaries before the Taieri River evolved to its present geometry, thereby limiting the placer gold content of the modern Taieri catchment.