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We sought to determine a compatible anticoagulant for routine haematological and physiological assessments with giant kokopu (Galaxias argenteus), an endemic New Zealand fish. We observed that blood treated with lithium heparin (LH) rapidly coagulated and haemolysed, making it unsuitable for G. argenteus. Dipotassium ethylenediaminetetraacetic acid (K2 EDTA) and trisodium citrate (citrate) effectively prevented blood coagulation. K2 EDTA-treated erythrocytes exhibited the least mean haemolysis and mean corpuscular fragility. Further studies into prolonged storage effects of citrate and K2 EDTA are recommended to find a compatible anticoagulant for use with G. argenteus blood.

This study characterised selected peripheral blood (PB) haematological parameters, liver, serum and muscle metabolic features in three- and five-year old male and female giant kokopu (Galaxias argenteus) broodstock reared indoor at 16°C. Sex and age did not affect PB total cell count, and haematocrit values. However, higher erythrocytes in five-year old fish, elevated thrombocyte and lymphocyte counts in three-year old fish indicate age-specific cellular regulation. Higher thrombocyte counts in female fish suggest sex-specific regulation. At a metabolic level, liver abundance for long chain saturated fatty acids were higher in males, while females had elevated levels of polyunsaturated fatty acids. Essential and non-essential amino acids in liver and serum were also elevated in females compared to males. These findings suggest differential allocation of fatty acids and amino acids to reflect requirements for gonadal, development and provisioning. Similarly, age significantly resulted in higher liver and serum abundances of some non-essential amino acids in three-year olds compared to five-year old fish, suggesting higher metabolism in younger fish. Overall, results enhance our understanding of sex- and age-based differences in fish haematology, muscle, liver, and serum metabolite profiles in healthy G. argenteus. Future studies should carefully consider potential age- and sex-specific differences in metabolic responses. This article is protected by copyright. All rights reserved.

The ability of different broodstock generations to provision lipids to their gametes is often overlooked in aquacultured freshwater fish. In this study we investigated the ability of two generation...

Globally, many freshwater fishes are declining in distribution and abundance, but for many species conservation measures are hindered by a limited knowledge of their ecology. Recent development of 12-mm half-duplex (HDX) passive integrated transponder (PIT) tags has broadened the potential application of this technology for studying habitat selection and migration of freshwater fishes. However, the limited read range of the smaller 12-mm PIT tags can limit their functionality in ecological studies. The present study used four migratory fish species to test the efficacy of different PIT antenna designs for detecting 12-mm HDX tags in small- and medium-sized rivers. Three types of pass-through antennae were created and coupled to either a single reader or multiplexor board. Across single-reader and multiplexor systems, the detection efficiencies for Giant Kokopu Galaxias argenteus, Shortfin Eel Anguilla australis, and New Zealand Longfin Eel Anguilla dieffenbachii ranged between 87% and 97%. Adult P...

Mahurangi Technical Institute (MTI) operates a commercial fish hatchery that conducts aquaculture research, acts as a teaching tool for aquaculture students, breeds native fish for reintroduction projects, and for supply to zoos and public aquariums for display, as well as breeding selected introduced species for biological control of aquatic weeds throughout New Zealand. This research arm has a long and successful history in the breeding and rearing of a number of fish species, including New Zealand native threatened freshwater-fish species. The Shortfin eel Anguilla australis, Giant kokopu Galaxias argenteus, Banded kokopu Galaxias fasciatus, Shortjaw kokopu Galaxias postvectis, Koaro Galaxias brevipinnis, Redfin bully Gobiomorphus huttoni, Common bully Gobiomorphus cotidianus, Giant bully Gobiomorphus gobioides, Cran's bully Gobiomorphus basalis, Freshwater shrimp Paratya curvirostris and Freshwater crab Amarinus lacustris have all been bred successfully at MTI. Of these native species, MTI has successfully closed the lifecycle of Giant kokopu, Banded kokopu, Cran's bully, Common bully, Freshwater shrimp and Freshwater crab. This paper focuses on work so far conducted to close the lifecycle of the Shortfin eel and the Giant kokopu.

We examined diel variation in prey selection by giant kokopu, Galaxias argenteus, in relation to diel variation in the abundance of drifting invertebrates in a second order stream in Otago, New Zealand in summer. Clear differences in both the quantity and composition of prey consumed was evident. Greater numbers of aquatic insects were consumed at night relative to the day, whereas more terrestrial insects were consumed by day relative to the night. Giant kokopu were selective in the prey consumed. Trichoptera dominated giant kokopu diet at night even though drift samples collected at night were dominated by Deleatidium mayflies. Results suggest that giant kokopu feed actively during night and day in summer, and that prey selection is influenced by interactions between factors including prey availability, prey characteristics and light.

The spatial organisation and behavioural interactions between giant kokopu (Galaxias argenteus) of varying sizes were investigated in two stream pools which varied in fish density. The spatial distributions offish in Pool A were more exclusive, exhibited less overlap, and appeared to be more stable than those for fish in Pool B. The distinct difference observed between the two pools may have been influenced by fish density which was lower in Pool A (0.27 fish/m2) than in Pool B (0.51 fish/m2). A linear, size (weight) related dominance hierarchy appeared to exist within both pools whereby the heaviest individual was the most dominant. Though primarily nocturnal in habit, the social structure and behaviour of giant kokopu (when active during the day) was comparable to that exhibited by other drift‐feeding fish in the Northern Hemisphere.

Nocturnal microhabitat selection in relation to size was examined for a New Zealand drift-feeding freshwater fish, the giant kokopu Galaxias argenteus in three coastal Otago streams. Evidence for ontogenetic shifts in microhabitat selection were observed, particularly with respect to water velocity and depth. Small (

The distribution of fish within eight small streams feeding into the lower Taieri and Waipori Rivers on the east coast of New Zealand's South Island was examined. A total of eight native and two introduced species were recorded. Eels (Anguilla spp.) and giant kokopu (Galaxias argenteus Gmelin) were the most widely distributed species being located in all streams surveyed. Common bullies (Gobiomorphus cotidianus McDowall) and brown trout (Salmo trutta Linnaeus) were also widely distributed being detected in seven and six of the streams respectively. Three streams of potential conservation significance were identified. These were Picnic Gully Creek which contained a significant population of banded kokopu (Galaxias fasciatus Gray), a Category C threatened species, and Cullens and Alex Creeks which contained significant populations of giant kokopu, a Category B threatened species. The population of giant kokopu in Cullens and Alex Creeks currently represents the largest known population of this spec...

The movements of giant kokopu Galaxias argenteus were recorded before, during, and after high-discharge events in two small streams using radiotelemetry. Giant kokopu remained within defined stream reaches during base flow conditions. During high-discharge events, individuals either stayed within their home reach, moved and settled elsewhere, or moved and returned to their home reach as flows subsided. The variable behavior exhibited by individual giant kokopu suggested that reasons for moving during floods are complex. Reasons that may have influenced movement during floods included reproduction and mate searching, lack of adequate refugia, or some combination of these. In many instances, individual giant kokopu appeared to exhibit adaptive behaviors in response to high discharges. Behaviors supporting this view included fish not moving during the highest floods, fish moving upstream during the peak discharge period, and fish making purposeful “micromovements” (movements

The stomach contents of 105 preserved specimens of giant kokopu, Galaxias argenteus (Gmelin 1789), collected from various locations around New Zealand between c. 1963 and 1994, were used to investigate giant kokopu diet. A total of 76 food taxa, predominantly invertebrates, were identified and categorised as either of aquatic or terrestrial origin from the 91 stomachs that contained food items. Aquatic Trichoptera, Gastropoda, and Hemiptera comprised 29.1, 12.6, and 14.4% by abundance respectively, and terrestrial Coleoptera 12.2% by abundance. Adult terrestrial Coleoptera were the most commonly occurring taxa, and were found in 59% of the stomachs that contained food. Food items of aquatic origin occurred in 94.5% of the giant kokopu stomachs that contained food and comprised 74.9% of the items by abundance. Although fewer items of terrestrial origin were encountered, they nevertheless appeared to be a significant component of the diet, and occurred in 83.5% of the giant kokopu stomachs that con...

The giant kokopu (Galaxias argenteus (Gmelin 1789)) is endemic to New Zealand, and is regarded as threatened. A perceived decline of the species has been attributed mostly to the loss and degradation of its habitat. To determine habitat requirements, information from the New Zealand Freshwater Fisheries Database, and from field surveys in the South Island were analysed. These indicated that five habitat features are important: in‐stream cover, deep water, low water velocity, proximity to the sea, and overhead shade/riparian cover. These features were important in two distinct regions surveyed and for both juvenile and adult fish. The effects of different types of riparian and in‐stream cover were examined, but it appeared that the presence of some form of cover was more important than its composition. The conservation and management of giant kokopu will probably continue to be based upon management of their habitat, and these processes will be enhanced by the knowledge of the species’ habitat req...

Juveniles of giant kokopu (Galaxias argenteus (Gmelin)) that had newly entered fresh water were captured, primarily from the Buller and Hokitika Rivers, New Zealand, between 5 November and 15 December (when sampling ceased). Age at migration estimated from otolith daily growth rings was mostly c. 104–140 days. There is a positive relationship between fish length and number of otolith growth rings at migration, though variation is broad. Back calculation to hatch indicated that hatching occurred 185–245 days after 1 January (4 July‐2 September); allowing 28 days for development, these data suggest that giant kokopu spawn between early June and early August.

To establish a method of gonad biopsy for ovarian tissue collection in the declining giant kokopu Galaxias argenteus (Gmelin 1789) as an alternative to lethal sampling in order to understand the species' reproductive biology.Six female giant kokopu weighing between 200 and 350 g were caught from the wild in early December of 2009 and transferred to a holding facility (Department of Zoology, University of Otago, Dunedin) where they were kept under a simulated natural photo-thermal regime for 10 months. Fish were repeatedly biopsied for ovarian tissue at near-monthly intervals (mean number of days between biopsies = 33) until ovulation.Ovarian samples were successfully collected from giant kokopu by biopsy for use in downstream analyses. Among a total of 23 biopsy events, a single death occurred when a two-layered suturing approach was used, highlighting the value of this method for study of the reproductive biology of valuable fish.This biopsy method may have implications for veterinary research on fish physiology, pathology, conservation and development, when repeated tissue samples need to be collected over a prolonged period of time or for general surgical manipulations on fish when accessing the coelom. Furthermore, this approach allows the implementation of a more powerful experimental design, as repeated measures reduces the variability of estimates due to the removal of inherent stage differences among individuals.

The effect of land use on fish community structure was examined at fifty‐five sites in tributaries draining exotic, indigenous forest and pastoral catchments in the Hakarimata range in March and April 1987. Using a model containing percentage woody debris, temperature, and substrate coarseness, 76% of the sites were classified into correct land uses by discriminant analysis. This indicated that differences in stream habitat, and hence of the fish fauna, were related to effects of changed land use rather than other confounding physical or geographical features of the streams in the catchments. Tributaries in indigenous forest were numerically dominated by banded kokopu (Galaxias fasciatus) and longfinned eel (Anguilla dieffenbachii), with redfinned bully (Gobiomorphus huttoni) and giant kokopu (G. argenteus) occasionally being caught. Pastoral streams below the forest generally supported higher densities and contained more species including the forested species above, Cran's bully (G. basalis), an...

Radio and acoustic telemetry have been used in 24 studies of freshwater fish in New Zealand. Although most native species are too small to carry these tags, studies using telemetry have been carried out on four of the larger species, i.e. lampreys (Geotria australis), shortfin and longfin eels (Anguilla australis and A. dieffenbachii) and giant kokopu (Galaxias argenteus). Among the introduced species, telemetry has been used to study movements of brown and rainbow trout (Salmo trutta and Oncorhynchus mykiss) in both rivers and lakes, chinook salmon (Oncorhynchus tshawytscha), koi carp (Cyprinus carpio) and bullhead catfish (Ameiurus nebulosus). To date, studies have almost exclusively been of short-term movements and seasonal migrations. Study objectives range from measuring microhabitats and home ranges to determining the extent of seasonal spawning migrations. The advent of progressively smaller tags will provide increased opportunities to use this technology on a wider range of fish species. Management implications of several studies are presented. Although biotelemetry studies have not yet been used in New Zealand, there are considerable opportunities for using such technology to increase understanding of fish energetics and also stress associated with catch-and-release practices in recreational fishing.