Species Of Galaxias Research Articles

Spatiotemporal patterns of research on Southern Hemisphere amphidromous galaxiids: A semi–quantitative review

AbstractAmphidromy is a distinctive life‐history strategy of some fish species that involves spawning in fresh or brackish water followed by dispersal to sea by newly hatched larvae, where they develop for a short period. Individuals then return to freshwater as juveniles, where they feed and grow, before maturing and spawning. Six amphidromous species from the Southern Hemisphere genus Galaxias (G. truttaceus, G. fasciatus, G. argenteus, G. postvectis, G. brevipinnis, G. maculatus) are recreationally, culturally, and economically important as the juveniles are harvested. Due to ongoing population declines and a lack of critical demographic information, there is growing concern about the management of the species. Here, we used semi‐quantitative review, culturomics, and bibliometric tools to analyse peer‐reviewed research conducted on the six amphidromous species of Galaxias to: (i) understand how spatiotemporal patterns of research have shifted over the last five decades, and (ii) identify critical research gaps. Forty percent of studies (n = 295) covered a spatial extent of 10 km or less and 87% of studies lasted less than 2 years – studies were largely small and short relative to the species' ranges and their longevity. Additionally, we found important research gaps; for example, studies on the effects of climate change and the associated effects of disturbance, and the marine phase are scarce in the peer‐reviewed literature. Finally, we suggest that quantitative models have been underutilized as tools for studying amphidromous galaxiids and should be embraced to answer questions not readily addressed with field and laboratory‐based techniques. If these species are to be effectively managed, their population dynamics across spatiotemporal scales must be understood and critical and long‐standing gaps in research knowledge addressed.

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.

Contrasting Patterns of Genetic Diversity and Divergence Between Landlocked and Migratory Populations of Fish Galaxias maculatus, Evaluated Through Mitochondrial DNA Sequencing and Nuclear DNA Microsatellites.

Galaxias species are interesting biogeographic models due to their distribution and different types of life cycles, with migratory and landlocked populations. To obtain a better understanding of the genetic consequences of the Quaternary glacial cycles in Galaxias maculatus, in this work we compared landlocked and migratory populations collected in areas that were differentially affected by ice advances and retreats. We included nine populations of G. maculatus, four collected from lakes (landlocked) and five from their associated estuaries/rivers (migratory) in three estuary-lake systems across southern Chile. Genetic analyses were performed using the mitochondrial control region and nine microsatellite loci. Genetic diversity measured with both markers was significantly higher in migratory than in landlocked populations across the study area. The levels of genetic differentiation showed higher differentiation among lakes than estuaries. Genetic diversity was higher in migratory populations located in areas that were less impacted by ice during Quaternary glacial processes. These results may be the consequence of recent recolonization of small freshwater bodies following the Last Glacial Maximum (LGM). Finally, the greatest differentiation was observed in populations that were exposed to continental ice advances and retreats during the LGM. Thus, in the present work we corroborate a pattern of differentiation between lakes and estuaries, using mtDNA sequences and microsatellite nuclear markers. This pattern may be due to a combination of biological factors, i.e., resident non-migratory behaviour or landlocking and natal homing-in, as well as geological factors, i.e., Expansion-Contraction Quaternary glacial biogeographic processes.

Reproductive ecology of a critically endangered alpine galaxiid.

Stocky galaxias Galaxias tantangara is a newly described freshwater fish restricted to a single population, occupying a 3 km reach of a small headwater stream in the upper Murrumbidgee River catchment of south-eastern Australia. This species is listed as critically endangered under IUCN Red List criteria, and knowledge of the species' ecology is critical for future conservation efforts to establish additional populations by translocation and captive breeding. This study details the first account of spawning and reproductive ecology of G. tantangara, including reproductive development, timing of spawning and a description of one spawning site. Peak gonadosomatic index was observed in March/April in males and in October in females. Absolute fecundity ranged from 211 oocytes for a 76 mm length to caudal fork (LCF) fish to 810 oocytes for a 100 mm LCF fish. The observation of spent females in mid-November 2017 and discovery of an egg mass 8 days later suggest that spawning had occurred, and over a relatively short period. Larvae were subsequently detected in monthly electrofishing surveys in December 2017. Findings from this study provide new understanding of existing and future threats to G. tantangara and have important implications for conservation management of not only this species but also other closely related threatened Galaxias species.

Contrasting evolutionary responses in two co-distributed species of Galaxias (Pisces, Galaxiidae) in a river from the glaciated range in Southern Chile.

Life-history traits are among the most important factors affecting population abundance and genetic diversity of species. Here, we analysed the genetic patterns of two Galaxias species with different life-history traits to investigate how these biological differences impacted their evolution in the Valdivia River basin, Southern Chile. We analysed mitochondrial DNA (mtDNA) sequences from 225 individuals of Galaxias maculatus and 136 of G. platei to compare patterns of genetic diversity, structure and demographic growth across the basin. Galaxias maculatus presented higher genetic diversity and higher genetic structure than G. platei. Demographic analyses showed G. maculatus kept a higher population size over time, with a signal of demographic expansion in the last 250 kyr. Whereas Galaxias platei, exhibited lower, but constant population size over time. Furthermore, haplotype networks revealed higher lineage diversity in G. maculatus with a tendency to occupy different areas of the basin. Coalescent simulations ruled out that genetic differences between species could be explained by stochastic processes (genetic drift), suggesting species-specific biological differences as responsible for the observed genetic differences. We discuss how differences in life-history traits and past glaciations interact to shape the evolutionary history of the two Galaxias species.

A Review of Galaxias (Galaxiidae) Fossils from the Southern Hemisphere

The Galaxiidae is a Southern Hemisphere family of freshwater fish, considered to be of Gondwanan origin based on the current distribution of species in New Zealand, Australia (including Tasmania), New Caledonia, Africa, South America, and on some associated and subantarctic islands. The fossil record of galaxiids is extremely sparse and geographically restricted. The only galaxiid fossils currently known come from several Miocene lakes in southern New Zealand. They include more than 100 articulated fishes, some remarkably preserving soft parts such as eyes and skin, skulls and jaw components, and more than 200 isolated otoliths. Common coprolites and in situ preserved gut content at one site (Foulden Maar) indicate the different diets of larvae and adult fish. These discoveries reveal a diverse Galaxias fauna, the presence of lake-locked populations, ontogenetic diet shifts, and representatives of several non-migratory Galaxias lineages associated with inland streams and lakes. There are at least six Galaxias species based on macrofossils and six separate otolith-based species from varied volcanic and regional lacustrine environments. This diversity points to southern New Zealand as a centre of biodiversity and speciation in Galaxiidae in the early to late Miocene.

Hydrographic correlates of within‐river distribution and population genetic structure in two widespread species of mountain galaxias (Teleostei, Galaxiidae) in southern Australia

Abstract Closely related species may have different patterns of distribution and spatial population structure in common landscapes, which can have implications for conservation of the species if they are vulnerable. The Australian mountain galaxias species complex has recently been split into 15 described species, 11 of which are threatened. In this study, we assessed the distribution and landscape genetic structure of two mountain galaxias species (Galaxias olidus and Galaxias oliros) in the Goulburn–Broken catchment (Murray–Darling Basin) in relation to hydrographic descriptors of river terrain, network and hydrology. We also assessed small‐scale population structure in juvenile G. oliros in tributary streams of the Goulburn River (the Granite Creeks). Analyses of distribution revealed that G. olidus mostly occurs in smaller streams at high elevations with steep valley slopes and high stream gradients downstream, whereas G. oliros mostly occurs in larger downstream waterways with higher magnitude and variability of stream flow. Population genetic structure in G. olidus was much greater than for G. oliros, with 17 of the 19 sampled locations resolved as genetically distinct populations for G. olidus, but only a single population revealed for G. oliros. Results for both species did not reflect the expectations of the stream hierarchy model or isolation‐by‐distance model. However, small‐scale spatial population structure in juvenile G. oliros in the Granite Creeks reflected the expectations of both stream hierarchy and isolation‐by‐distance models, suggesting that population structure of juveniles of this species reflects some level of spatial aggregation of closely related individuals that probably diminishes as the population ages. Higher landscape genetic structure in G. olidus was correlated with steeper stream and valley slopes, whereas no population genetic correlations were significant for G. oliros. Genetic diversity in G. olidus was higher in areas of greater hydrological variability, suggesting that populations in hydrologically variable areas function as a metapopulation and have a more diverse gene pool than populations in areas with lower hydrological variability. In contrast, genetic diversity in G. olidus was lower in higher elevation areas with steep valley slopes, suggesting that smaller but more stable populations occur in high elevation streams with high perenniality and low interannual variability of flows. Our results are consistent with other studies that highlight the importance of supporting natural hydrological regimes and natural patterns of hydrological connectivity for conservation of vulnerable freshwater fish.

Extreme Positive Selection on a New Highly-Expressed Larval Glycoprotein (LGP) Gene in Galaxias Fishes (Osmeriformes: Galaxiidae)

We describe the intron-exon structure and DNA/protein sequences of a new larval glycoprotein (LGP) gene from nine species of galaxiid fish. The gene has a distant similarity to Danio THP (Tamm-Horsfall urinary glycoprotein; uromodulin) and cichlid SPP120 (seminal plasma glycoprotein) due to conserved features of its zona pellucida (ZP) domain, including eight highly conserved cysteines and a consensus furin cleavage site. Using a combination of 454 sequencing of cDNA and exon-primed intron-spanning sequencing of genomic DNA, we obtained full sequences of the coding region (996 bp) and its intervening sequences (1,459 bp). LGP shows an exceptionally strong signal of positive selection over the entire coding region, as evidenced by d(N)/d(S) values >1. Across nine species of Galaxias, 87/332 (26%) amino acid residues are variable, compared with 9/386 (2%) for mitochondrial cytochrome b (cytb) in the same group of species. Across 36 interspecific pairwise comparisons, genetic distances are in all cases larger for coding region than for introns, by a factor of 2.4-fold on average. Reading frame, gene structure, splice sites, and many ZP motifs are conserved across all species. Together with the fact that the gene is expressed in all species, these results argue clearly against the possibility of a pseudogene. We show by 454 sequencing and quantitative polymerase chain reaction that the transcript is abundant (ca. 0.5%) in newly hatched larvae and appears to be almost absent from a range of adult tissues. We postulate that the strong Darwinian evolution exhibited by this protein may reflect some type of immunoprotection at this vulnerable larval stage.

Heavy metals: confounding factors in the response of New Zealand freshwater fish assemblages to natural and anthropogenic acidity

Acidification of freshwaters is a global phenomenon, occurring both through natural leaching of organic acids and through human activities from industrial emissions and mining. The West Coast of the South Island, New Zealand, has both naturally acidic and acid mine drainage (AMD) streams enabling us to investigate the response of fish communities to a gradient of acidity in the presence and absence of additional stressors such as elevated concentrations of heavy metals. We surveyed a total of 42 streams ranging from highly acidic (pH 3.1) and high in heavy metals (10 mg L − 1 Fe; 38 mg L − 1 Al) to circum-neutral (pH 8.1) and low in metals (0.02 mg L − 1 Fe; 0.05 mg L − 1 Al). Marked differences in pH and metal tolerances were observed among the 15 species that we recorded. Five Galaxias species, Anguilla dieffenbachii and A nguilla australis were found in more acidic waters (pH< 5), while bluegill bullies ( Gobiomorphus hubbsi) and torrentfish ( Cheimarrichthys fosteri) were least tolerant of low pH (minimum pH 6.2 and 5.5, respectively). Surprisingly, the strongest physicochemical predictor of fish diversity, density and biomass was dissolved metal concentrations (Fe, Al, Zn, Mn and Ni) rather than pH. No fish were detected in streams with dissolved metal concentrations > 2.7 mg L − 1 and nine taxa were only found in streams with metal concentrations < 1 mg L − 1. The importance of heavy metals as critical drivers of fish communities has not been previously reported in New Zealand, although the mechanism of the metal effects warrants further study. Our findings indicate that any remediation of AMD streams which seeks to enable fish recolonisation should aim to improve water quality by raising pH above ≈ 4.5 and reducing concentrations of dissolved Al and Fe to < 1.0 mg L − 1.

Galaxias fossils from Miocene lake deposits, Otago, New Zealand: The earliest records of the Southern Hemisphere family Galaxiidae (Teleostei)

Galaxiid fishes are commonly assumed to exhibit a Gondwanan distribution, but little fossil evidence has been available to support or refute this assumption until now. Here we report on three species of fossil Galaxias, represented by exquisitely preserved, almost entire skeletons, together with jaw and skull fragments, from several Miocene lacustrine deposits in Otago, South Island, New Zealand. These are the only certain Galaxias fossils, and provide unequivocal evidence that the genus was abundant, and taxonomically and ecologically diverse in the New Zealand region before 23 million years ago. One new species, Galaxias effusus, from an Early Miocene diatomite deposit near Middlemarch is described on the basis of low vertebral count, short caudal peduncle, expansive dorsal, caudal and anal fins, rounded to truncate caudal fin, with 15 principal caudal fin rays. The intact skeletons of G. effusus confirm that they inhabited a deep, stratified maar lake with cool, anoxic bottom water. The maar lake was completely landlocked, from sedimentological evidence, and this species must have been non‐migratory. Disarticulated fish jaws and skull fragments from Early Miocene mudstones near Bannockburn are likely to be from a second large species of Galaxias on the basis of dentary, premaxilla and parasphenoid size and morphology. These disarticulated fish remains from a regionally extensive inland lake system indicate decomposition and/or predation in shallow nearshore environments, but we have no evidence yet of migratory behaviour. New specimens of G. kaikorai Whitley from Late Miocene diatomite deposits near Dunedin confirm its morphological similarity to the living G. brevipinnis. The occurrence and diversity of galaxiids in lakes of early and Late Miocene age in southern New Zealand can be explained by either oceanic dispersal across the Southern Hemisphere at any time during the Cenozoic, relict Gondwanan distributions or, most likely, an ancient Gondwanan origin overprinted by Cenozoic dispersal.

The possible adaptive advantages of terrestrial egg deposition in some fluvial diadromous galaxiid fishes (Teleostei: Galaxiidae)

AbstractSeveral diadromous New Zealand and Australian species of Galaxias are now known, or suspected, to deposit their eggs amongst riparian vegetation or substrates either supratidally in estuaries or in forested streams in locations that are only temporarily submerged by elevated water levels. The eggs develop in a humid atmosphere and hatch when the egg deposition sites are resubmerged; a significant role for agitation in stimulating hatching seeming likely. There are risks from the eggs becoming dehydrated, and also from a failure by water to resubmerge the eggs before they have exhausted their energy resources. Hatching is triggered by elevated flows, perhaps being an outcome of agitation of the eggs. Elevated flows may also increase the rate of downstream transport of the larvae, facilitating survival during dispersal to sea from spawning sites in streams that may be long distances inland. Hatching during flood events may favour survival of the larvae because turbid flows may provide ‘cover’ for the larvae as they emigrate to sea. Risks from egg predation by aquatic predators may be replaced by risks from terrestrial predators.

Genetic structuring in Andean landlocked populations of Galaxias maculatus: effects of biogeographic history

AbstractAim To test whether the genetic diversity of diadromous and landlocked populations of the small puyen Galaxias maculatus (known as jollytail in Australia and inanga in New Zealand) follow the same structuring patterns observed for migratory and non‐migratory species of the genus Galaxias. This work also aimed to test whether the genetic structuring of a group of populations could be predicted from differences in the geomorphologic history of the region they inhabit.Location Eight landlocked populations were sampled from cold‐temperate lakes in north‐western Patagonia. The study area could be split latitudinally into two sectors that differed in their geomorphology, each of them hosting four populations. The southern sector shows evidence of a higher degree of glacial coverage, and the lakes are probably remnants of a big proglacial palaeolake. Lakes in the northern sector, on the other hand, suggest no common origin.Results Significant genetic structuring was found among the studied populations (Θ = 0.188), being the highest value reported to date for the species. Significant correlation was found between genetic diversity and lake area and perimeter. Diversity also showed a slight latitudinal variation suggesting the presence of genetically distinct groups of populations. The comparison of populations from the two geographical sectors showed that those from the north had a higher diversity, more private alleles and strong structuring, while those from the south were less diverse and much more homogeneous.Main conclusions Non‐migratory populations of G. maculatus show much higher values of genetic structuring than those reported for diadromous populations. This follows the pattern seen when comparing migratory and non‐migratory species of Galaxias. This agrees with population genetics theory which predicts that restricted gene flow would result in greater among‐population divergence. Also, differences between northern and southern populations agreed with what was predicted by the geomorphologic history of the study area. During the Last Glacial Maximum ice cover in that region may have reduced the habitat of G. maculatus to a refuge with an impoverished gene pool. When the ice receded, leaving a great proglacial lake, that former population expanded and became fragmented after water levels descended. This resulted in present day lakes harbouring homogeneous populations with reduced diversity. The northern sector, in contrast, was less affected by glaciers, resulting in more geomorphologically stable lakes holding genetically diverse populations.

A new longjaw galaxias species (Teleostei: Galaxiidae) from the Kauru River, North Otago, New Zealand

A population of “longjaw galaxias”, long known to be present in the Kauru River, a small tributary of the Kakanui River in North Otago, is shown to be a distinct species using both morphological and molecular characters. It is described here as Galaxias cobitinis n. sp., which has: origin of anal fin anterior to that of dorsal fin, only 15 principal caudal fin rays, only 5 pelvic fin rays, and only 51–53 vertebrae. In these and other morphological characters it differs from G. prognathus Stokell. One specimen from the Hakataramea River, lower Waitaki River system appears to also be G. cobitinis. Molecular evidence suggests long isolation from the Kauru River of “true” longjaw galaxias G. prognathus and from rivers draining the high Southern Alps (type locality: Wilberforce River, tributary of the Rakaia River), perhaps dating back as long as 11–4 million years ago (late Miocene‐early Pliocene). This prolonged isolation contrasts with hypothesised more recent isolation of populations of the Galaxias vulgaris species group in the Kakanui River from other populations of that species group. Thus, sympatric species of Galaxias have contrasting biogeographic histories in the Kakanui River.

Fine‐scale genetic structuring in endemic galaxiid fish populations of the Taieri River

Many of New Zealand's Galaxias species have declined in abundance this century. Some stream‐resident species are now restricted to sections of tributaries above waterfalls >3 m in height that act as barriers to the predatory brown trout (Salnto trutta). It has been suggested that these spatially isolated populations are also genetically isolated and as a result experience restricted gene flow. We used isozyme electrophoresis to test this hypothesis. Comparisons were made between and within tributaries at sites separated by waterfalls. Results from six polymorphic loci showed evidence of genetic heterogeneity among populations of G. anomalus and G. depressiceps from tributaries of the Taieri River system, South Island, New Zealand. In one instance, heterogeneity was found within a single tributary. This demonstrates that gene flow among populations is restricted and that waterfalls are likely to be a significant influence in controlling galaxiid population structure.

Reproductive biology, species status and taxonomic relationships of four recently discovered galaxiid fishes in a New Zealand river.

The reproductive biology of four recently discovered, largely allopatric non-migratory Galaxias species in the Taieri River, New Zealand, was compared with the closely related Galaxias vulgaris. Timing of spawning was similar (late winter/spring) but spawning habitat, spawning behaviour and nest structure differed among the Taieri species and G. vulgaris. Patterns of fecundity also differed among the Taieri species but, with G. vulgaris, they form a distinct group of galaxiids with maxima of 800-1500 eggs having diameters of 2·3-2·8 μn. The different spawning behaviours of the Taieri galaxiids, in particular the differences in spawning orientation, provide evidence for prezygotic isolating mechanisms and support their status as separate species. In cladistics terms, the results indicate that Galaxias anomalus, G. eldoni and G. vulgaris are sister taxa, while G. depressiceps and Galaxias sp. form a second cluster.

Affinities, generic classification and biogeography of the Australian and New Zealand mudfishes (Salmoniformes: Galaxiidae).

The Australian Galaxias cleaveri, resembles the three New Zealand mudfishes (Neochanna spp.) in general external morphology. It is the least specialised of a transformation series that includes all four mudfishes, in which the body is elongated, eyes are small, anterior nostrils long, tubular and forward directed, dorsal and anal fins low and long, flanges on the caudal peduncle well developed, pectoral fins small, paddle-shaped, and high on sides behind head, and pelvic fins reduced or lost. Unique specialisations in the vomerine-ethmoid region of the cranium and in the form of the pectoral girdle support the view that these four species are a monophyletic group. The Australian species is therefore included in Neochanna. The presence of a marine larval and juvenile life stage in the Australian species (diadromy) probably explains the distribution of the genus, with New Zealand species together derived from the Australian one or their common ancestor by dispersal across the Tasman Sea in prevailing ocean currents. The biogeography of the Australian and New Zealand species is consistent with post-Oligocene geology, and in particular with events during and since the Pleistocene. McDoWALL, RM., 1997. Affinities, generic classification and biogeography of the Australian and New Zealand mudfishes (Salmoniformes: Galaxiidae). Records of the Australian Museum 49(2): 121-137. The genus Neochanna was established by Giinther (1867) to contain a small, cigar-shaped fish found when drains were being dug in swamplands on the West Coast of the South Island of New Zealand; it was described as N. apoda (Fig. ID). While apparently a galaxiid (Galaxiidae) from its posterior dorsal fin and lack of scales, it was distinguished from Galaxias species by lacking pelvic fins, having flattened incisorlike jaw teeth, no endopterygoid teeth, long-based and low dorsal and anal fins that are nearly confluent with a distinctly rounded caudal fin, elongated, tubular anterior nostrils that point forwards, and small eyes (McDowall, 1970). Known commonly as brown mudfish, it became well-known as a fish often found, semi-torpid and aestivating, in damp locations from which water had dried up-beneath logs and stumps, down old root holes around the bases of forest trees, and in similar, damp places where water is ephemeral

Two further new species of Galaxias (Teleostei: Galaxiidae) from the Taieri River, southern New Zealand

Two new species of Galaxias have overlapping distributions in the lower Taieri River catchment, Otago, although not as yet found in sympatry. Galaxias pullus n.sp. is known from several tributaries of the Waipori River up‐ and downstream of Lake Mahinerangi, and also from a tributary of the Waitahuna, part of the Clutha River catchment. Galaxias eldoni n.sp. comes from several small tributaries of the lower Taieri near Outram and Middlemarch, from a tributary of the Waipori River below Lake Mahinerangi, from a tributary of the lake, and also a west branch tributary of the Tokomairiro River. These new species belong within the Galaxias vulgaris species‐group, which otherwise includes the nominate species, G. anomalus and G. depressiceps. Most populations of this species‐group south of the Waitaki River are not G. vulgaris (sensu stricto), but belong to one of four other species now recognised from the region. The known distributions probably reflect a combination of incomplete knowledge and fragmentation of ranges resulting from the effects of introduced species.

A new species ofGalaxias(Pisces:Galaxiidae) from Chatham Island, New Zealand

A new species of galaxiid fish from a peat lake on Chatham Island is described. This small freshwater fish is sufficiently distinct to have no obvious close relatives from among the other species of Galaxias in New Zealand. It is readily identified by the presence of pronounced caudal flanges and a moderately forked caudal fin.

Evaluation of subcutaneously implanted visual implant tags and coded wire tags for marking and benign recovery in a small scaleless fish, Galaxias truttaceus (Pisces: Galaxiidae)

Visual implant (VI) tags and coded wire tags (CWTs) were tested as methods for marking a small galaxiid fish, Galarias truttaceus, in such a way as to allow benign information recovery. VI tags were implanted beneath the skin of the preoperculum and CWTs were implanted between caudal fin rays. Both types of tag were easily implanted into fish &gt;90 mm total length (4-5 g). Retention rates of both tag types were evaluated under field conditions. Retention of VI tags implanted in the preoperculum was estimated at 100% after 14 days and 92% after 131 days. There was a loss of 8-18% of CWTs within the first four weeks after tagging. Tag loss continued more gradually thereafter and retention was estimated at 71% after 131 days. It was demonstrated that both types of tags could be applied successfully to four other species of Galaxias.

Adaptative Radiation of the Retina in Galaxiidae (Salmoniformes)

The retinas of seven galaxiid species collected from different habitats in Tasmania were investigated by light microscopy. There are remarkable differences between Galaxias and Paragalaxias species. The retinas of Galaxias species are characterised by a less dense retinal epithelial pigment (REP), large numbers of short and long rods, the presence of a tapetum, and stable (non-responsive) single cones in dark-adapted specimens. On the other hand, the common retinal features in Paragalaxias species include few large rods and many cones, the presence of a tapetum, lower summation and a pattern of retinomotor responses not unlike that of most other teleosts. There is no striking retinal feature that could be related to differences in their clear or turbid habitats. In spite of its probably being nocturnal, the retinal structure of P. dissimilis is basically similar to that of other diurnal Paragalaxias species. Some of the ecological constraints placed upon these species are also discussed.