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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.

SUMMARY 1. Within-species phenotypic variation is hugely variable and may play a role in determining the range of habitats a species can exploit. Our study addressed two main questions: 1. does phenotypic variation allow some species (i.e. habitat-generalists) to use heterogeneous habitats and 2. are habitat-generalists more variable than species occupying relatively homogeneous environments (i.e. habitat-specialists)? 2. We examined the morphology of the common bully (Gobiomorphus cotidianus), a habitatgeneralist eleotrid fish found in lakes and rivers throughout New Zealand. We also compared the level of morphological variability in common bullies with that in the closely related redfin bully (Gobiomorphus huttoni), a habitat-specialist of moderate- and fast-flowing rivers. 3. Common and redfin bullies were collected from the South Island of New Zealand. A series of body and fin measurements were made, and cephalic dorsal head pores of the mechanosensory lateral-line system were counted. The pores and associated canal neuromasts are important for prey detection and predator avoidance in other species, particularly, in turbulent conditions where the effectiveness of superficial neuromasts may be compromised. 4. The common bully had more dorsal head pores in fish from rivers than in those from lakes. This pattern was apparent only in adults, suggesting that selective pressures associated with adult habitat, be it rivers or lakes, are responsible. 5. As expected, there was greater phenotypic variability in the generalist common bully than in the specialist redfin bully, particularly with regard to the sensory pores, suggesting their importance for survival in turbulence. 6. We identified habitat-related patterns in phenotypic variability in a generalist species and demonstrated a link between phenotypic variability and habitat breadth. Variation in the common bully may explain its ability to occupy a range of habitats.

The use of subsurface sediments by benthic prey as spatial refugia from predators can potentially influence predator consumption, and hence density-dependent relationships. We studied how predatory fish affect subsurface sediment use by spiny- and smooth-shelled morphs of the mudsnail, Potamopyrgus antipodarum, on New Zealand’s South Island. Spines reduce consumption risk by small benthic fishes (e.g., bullies [Gobiomorphus spp.]). Thus, we predicted that spiny morphs would be more likely to use sediment surfaces with relatively high algal food supplies than the more vulnerable smooth morphs when exposed to fish predators. Epi- and endobenthic samples from 5 streams with fish showed that ∼80% of snails typically were retrieved from subsurface sediments, whereas only 33% of snails from fishless Jackson’s Creek occurred in subsurface sediments. A laboratory experiment revealed that significantly more snails used subsurface sediments when with common bullies (G. cotidianus) than when without. Subsurf...

Common native fish species that are rare in New Zealand rivers with high suspended solids (SS) concentrations were identified to determine which species were likely to be most affected by high SS concentrations. Mortality rates for the three most sensitive species (banded kokopu Galaxias fasciatus, redfin bully Gobiomorphus huttoni, common smelt Retropinna retropinnd) were measured over a range of SS concentrations to identify lethal concentrations. The survival of banded kokopu and redfin bully was not reduced by SS concentrations up to 43 000 g m−3; however, the 24‐h survival of common smelt was reduced by SS concentrations over 1000 g m−3, and its median lethal concentration (LC50) was close to 3000 g m−3. SS concentrations over 3000 g m−3 for more than 24 h will therefore reduce smelt but not affect the mortality of most other common native fish species. Although mortality from high concentrations of SS can account for the scarcity of smelt in rivers with high SS concentrations, mortality fro...

Using data from existing studies, assemblages of freshwater fishes and decapod crustaceans were examined at 39 sites in urbanised catchments and 57 sites in forested (reference) catchments within the greater Auckland region, New Zealand. Eleven native and 1 exotic fish species and 2 native decapod crustacean species were recorded. Species richness and fish Index of Biotic Integrity (IBI) scores were lower overall in streams in urbanised catchments. Shortfin eel (Anguilla australis) and mosquitofish (Gambusia affinis) were more dominant in urban streams; all other commonly occurring species were found significantly more often in reference streams. Non‐diadromous native species (Cran's bully (Gobiomorphus basalts) and freshwater crayfish (Paranephrops planifions)) were absent from urban streams, but relatively abundant in reference streams. This absence of non‐diadromous species, together with the urban occurrence of five diadromous species suggests that migratory barriers pose less of a threat to ...

Alternative transmission strategies are common in many parasitic organisms, often representing discrete phenotypes adopted in response to external cues. The facultative truncation of the normal 3-host life-cycle to a 2-host cycle in many trematodes provides an example: some individuals mature precociously, via progenesis, in their intermediate host and produce eggs without the need to reach a definitive host. The factors that determine how many and which individuals adopt the truncated life-cycle within a parasite population remain unknown. We investigated the occurrence of progenesis in the trematode Stegodexamene anguillae within its fish intermediate host. Location within the host was a key determinant of progenesis. Although the size and egg output of progenetic metacercariae encysted in host gonads did not differ from those of the few progenetic metacercariae in other host tissues, the likelihood of metacercariae becoming progenetic was much higher for those in the gonads than those elsewhere in the host. Progenetic parasites can only evacuate their eggs along with host eggs or sperm, providing a link between the parasite's transmission strategy and its location in the host. Host size and sex, and the presence of other parasite species in the host, did not affect the occurrence of progenesis in S. anguillae. However, the proportion of metacercariae in host gonads and the proportion of progenetic metacercariae both decreased with increasing numbers of S. anguillae per host. These results suggest that progenesis is adopted mostly by the parasites that successfully establish in host gonads. These are generally the first to infect a fish; subsequent arrivals settle in other tissues as the gonads quickly become saturated with parasites. In this system, the site of encystment within the fish host both promotes and constrains the adoption of a facultative, truncated life-cycle by the parasite.

Densities of larval smelt (Retropinna retropinna) and common bullies (Gobiomorphus cotidianus) were estimated by a closing Wisconsin drop-net on two occasions following the spring/summer spawning season in 11 geographically localised lakes varying in size and trophic status. Mean densities of smelt ranged from 0 to 65 fish m−2 and were directly related to water clarity as determined by secchi disc depth. In contrast, densities of larval bullies ranged from 0 to 117 fish m−2 and were inversely related to water clarity. Larval smelt dominated in all the clear water, oligotrophic lakes, but bullies dominated in lakes where water clarity was less than 6 m. The depth distribution and depth range for schools of juvenile smelt was also reduced in turbid lakes. As the ability of juvenile smelt to feed on zooplankton is not reduced by turbidity, and as predation by trout on smelt decreases in turbid lakes, these two factors are not responsible for the decline of smelt in the more turbid, productive lakes. We propose that reduced larval recruitment caused by a higher egg mortality is responsible. A higher egg mortality would be expected in such lakes because of increased siltation of littoral spawning substrates, and increased predation by common bullies.

Genetic differentiation among populations of the Tarndale bully and three other Gobiomorphus species was investigated with mitochondrial DNA sequence variation. Sequences from parts of the mitochondrial cytochrome b gene and control region were obtained for 70 bullies. Specimens of Tarndale bully, known from only five small tarns in the northern South Island of New Zealand, clustered with specimens of common bully from both North Island and South Island locations, and not upland or Cran's bullies. The molecular results are discussed in relation to the morphometric and meristic variation, and the origin of the Marlborough tarns. It is concluded that populations of bullies in the Marlborough tarns are a lake‐locked ecophenotype of the common bully and not a phylogenetic species.

We determined the effects of logging, both with and without a riparian buffer strip, on the native fish fauna at 27 stream sites in an exotic pine (mainly Pinus radiata) forest on the Coromandel Peninsula, New Zealand. Fish abundance at the logged sites was compared with reference sites in both unlogged pine and native forest. The abundance of Anguilla dieffenbachii (Gray) and Anguilla australis (Richardson) was not significantly affected by logging. However, the abundance of Galaxias fasciatus (Gray) and Gobiomorphus huttoni (Ogilby) was. There were fewer Ga. fasciatus at the logged sites without buffers than at the reference sites, but more at the logged sites with buffers. The abundance of Go. huttoni was higher at the logged sites than at the reference sites, and was highest at the logged sites with riparian buffers. Overall, the different, species‐specific responses to logging maximised total fish numbers at the logged sites. As total fish numbers, the abundance of Ga. fasciatus, and species...

Larval and juvenile fish drifting on ebb tides were collected from early summer to mid autumn at various locations in the Taieri River and Waipori River estuary, South Island, New Zealand. A total of seven species of fishwere recorded, however only three species were regularly collected. These were the larval common bully (Gobiomorphus cotidianus McDowall), larval inanga (Galaxias maculatus Jenyns), and postlarval cockabully (Tripterygion nigripenne Valenciennes). Common bully densities were highest in mid January, with the highest densities being recorded drifting out of Lake Waihola. Inanga densities were highest in March and April, with the highest densities being recorded in the channels draining wetland areas where extensive tidal inundation of riparian vegetation occurred. Cockabully were recorded from February to April, mostly at more downstream sites. Inland penetration by marine species was considerable, with two marine species, clingfish (Trachelochismus pinnulatus Forster) and smooth leatherjacket (Parika scaber Forster), being recorded c. 12 km upstream in late summer.

Chemicals exuded by predators (kairomones) are known to induce the daytime descent of several species of Northern Hemisphere Daphnia. The vertical migration of New Zealand's native Dapknia carinata King has not been studied, however, and its response to kairomones is not known. We compared the behavioural responses of D. carinata to water from around two predatory fish, common bully (Gobiomorphus cotidianus) and inanga (Galaxias maculatus), an aquatic insect (Anisops wakefieldi), and several concentrations of trimethylamine (TMA), a fish‐mediated chemical. The responses of Daphnia were assessed in nine trials by comparing their vertical distribution in cylinders of water before and after exposure to water that had contained each predator, or TMA. D. carinata did not alter their vertical distribution in response to water from around Anisops. However, they descended when exposed to water from around inanga in 83% of trials and common bully in 67% of trials. They also descended in response to TMA in...

Laboratory tank experiments were used to determine the effect of turbidity levels ranging from 0–640 Nephelometric Turbidity Units (NTU) on mean feeding rates for each species. Mean feeding rates for banded kokopu (Galaxias fasciatus), smelt (Retropinna retropinna), inanga (G. maculatus), and common bullies (Gobiomorphus cotidianus) were all reduced by increased turbidity, but significantly so only for banded kokopu and inanga. Banded kokopu was the most sensitive species as feeding rates at 20 NTU were significantly lower than in clear water, compared with levels over 160 NTU for the other species. Feeding rates for redfinned bullies (Gobiomorphus huttoni) increased with turbidity up to 40 NTU then decreased. Reductions in feeding rate at elevated turbidity levels were the result of a reduced inability to feed, rather than to stress, as exposure to the highest turbidity level did not reduce feeding motivation or appetite. Feeding tests in the dark indicated that, whereas vision was important for...

The upland bully is a prolific and widespread member of New Zealand freshwater fish communities that may mature at age 1 (or earlier). It begins spawning in spring, laying as many as eight clutches of eggs over the spring and summer, at periods as brief as 13 days. Ovaries contain two modes of maturing oocytes, so that oogenesis must be continual during the spawning season. This poses difficulties in fecundity estimation, which were solved by captive rearing. The ovoid eggs are about 2 mm long; egg size declines with clutch number during the summer, but increases with fish size. Clutch size varied, in 70 spawnings, from 121 to 880 eggs, with total seasonal fecundity up to >5000 eggs. The production of multiple clutches greatly increases seasonal fecundity and may explain the success of this species in sometimes unreliable or harsh environments.

The avoidance response of the migratory juvenile stage of six species of diadromous fish to different levels of suspended solid (SS) was determined in the laboratory using a two‐choice avoidance tank. Trials were mostly conducted with resuspended sediment from the outlet of Lake Waahi, New Zealand, but a series of tests was also conducted with kaolin for comparison. Banded kokopu (Galaxias fasciatus) was the most sensitive species, displaying a 50% avoidance response to kaolin and Waahi silt at 17 and 25 NTU, respectively. Koaro (Galaxias brevipinnis) and inanga (Galaxias maculatus) were found to be less sensitive than banded kokopu, with a 50% avoidance response to Waahi silt at 70 and 420 NTU, respectively. Shortfinned and longfinned elvers (Anguilla australis and/1, dieffenbachii), and redfinned bullies (Gobiomorphus huttoni) showed no avoidance behaviour, even at the highest turbidities (1100 NTU) tested. Based on these laboratory results, and until field testing is undertaken, a limit of abo...

Understanding migratory life histories is critical for the effective management and conservation of migratory species. However, amphidromous migrations (fish hatch in streams, immediately migrate to the sea for a feeding period and return to fresh water as juveniles) remain understudied owing to the difficulties of tracking tiny larval fish. Despite this, it has widely been assumed that amphidromous fish have open, resilient populations, with marine-rearing larvae dispersing widely during their pelagic phase. In the present study we tested the hypothesis that when an alternative freshwater pelagic habitat is available, non-diadromous recruitment will be the dominant process in sustaining amphidromous fish populations, with implications for their connectivity and resilience. Otolith microchemical analyses of five species (three Galaxias (Galaxiidae), two Gobiomorphus (Eleotridae)) from paired systems on the South Island of New Zealand indicated that when a suitable freshwater pelagic habitat existed downstream, non-diadromous recruitment was the primary population-sustaining process, typically contributing >90% of recruits. In addition, not all species recruited from all lakes, indicating the importance of the largely unstudied role of species-specific amphidromous larval requirements. The results of the present study emphasise the need to better understand the dynamics of individual populations of amphidromous fish, and highlight the importance of understanding species-specific early life history requirements to fully understand their distributions and management needs.

Goal: To examine the phylogenetic relationships within Gobiomorphus to explore Australasian biogeography, origins (single or multiple), and evolutionary loss of a marine life stage (loss of diadromy). Methods: We analyse a fragment of the mitochondrial DNA (Cyt-b) using phylogenetic analyses, and use several meristics (spines, rays, and vertebrae) in a discriminant function analysis. Organisms: All nine species of the genus Gobiomorphus (Eleotridae) found in New Zealand and Australia, with the two Australian Philypnodon species included as outgroup taxa. Conclusions: Monophyly of the genus and all seven New Zealand species was strongly supported. The New Zealand Gobiomorphus are likely to be the result of a single introduction and to have been isolated from Australia since the Miocene or Pliocene (∼18–28 Myr ago). These dates correspond well to the oldest fossil in New Zealand dated at 16–20 Myr. Diadromy was consistently at the root of the New Zealand group, and non-diadromy and morphological diversification among these species appears to have occurred relatively recently, with meristic comparisons supporting the molecular analyses. However, among the non-diadromous forms, species morphology contrasts with the molecular data suggesting a recent evolutionary history driven by ecological selection. Refereed/Peer-reviewed

Background Many postglacial lakes contain fish species with distinct ecomorphs. Similar evolutionary scenarios might be acting on evolutionarily young fish communities in lakes of remote islands. One process that drives diversification in island freshwater fish species is the colonization of depauperate freshwater environments by diadromous (migratory) taxa, which secondarily lose their migratory behaviour. The loss of migration limits dispersal and gene flow between distant populations, and, therefore, is expected to facilitate local morphological and genetic differentiation. To date, most studies have focused on interspecific relationships among migratory species and their non-migratory sister taxa. We hypothesize that the loss of migration facilitates intraspecific morphological, behavioural, and genetic differentiation between migratory and non-migratory populations of facultatively diadromous taxa, and, hence, incipient speciation of island freshwater fish species. Results Microchemical analyses of otolith isotopes (88Sr, 137Ba and 43Ca) differentiated migratory and non-migratory stocks of the New Zealand endemic Gobiomorphus cotidianus McDowall (Eleotridae). Samples were taken from two rivers, one lake and two geographically-separated outgroup locations. Meristic analyses of oculoscapular lateral line canals documented a gradual reduction of these structures in the non-migratory populations. Amplified fragment length polymorphism (AFLP) fingerprints revealed considerable genetic isolation between migratory and non-migratory populations. Temporal differences in reproductive timing (migratory = winter spawners, non-migratory = summer spawners; as inferred from gonadosomatic indices) provide a prezygotic reproductive isolation mechanism between the two ecotypes. Conclusion This study provides a holistic look at the role of diadromy in incipient speciation of island freshwater fish species. All four analytical approaches (otolith microchemistry, morphology, spawning timing, population genetics) yield congruent results, and provide clear and independent evidence for the existence of distinct migratory and non-migratory ecotypes within a river in a geographically confined range. The morphological changes within the non-migratory populations parallel interspecific patterns observed in all non-migratory New Zealand endemic Gobiomorphus species and other derived gobiid taxa, a pattern suggesting parallel evolution. This study indicates, for the first time, that distinct ecotypes of island freshwater fish species may be formed as a consequence of loss of migration and subsequent diversification. Therefore, if reproductive isolation persists, these processes may provide a mechanism to facilitate speciation.

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...

Worldwide, human-mediated disruption of river networks by artificial structures negatively affects migratory fish species. To creatively solve part of this problem, we assessed the effectiveness of mussel spat ropes for improving fish passage past perched culvert structures. We used a before–after–control–treatment design to test our hypothesis that relative abundances of ‘young-of-the-year’ migratory fish species would increase following rope installation in a New Zealand stream. Results following remediation indicated a significant three- to four-fold increase in fish abundance relative to a control stream. Although four species (banded kokopu (Galaxias fasciatus), redfin bullies (Gobiomorphus huttoni), longfin eels (Anguilla dieffenbachii) and shortfin eels (Anguilla australis)) were present at both the treatment and control stream sites, the increased fish relative abundance at the treatment site was driven primarily by an increase in ‘young-of-the-year’ banded kokopu. The present study has shown that mussel spat ropes can significantly improve fish relative abundances above severely perched culverts, but may not be effective for all species present. Future use of ropes for evaluating passage efficacy for other species, and for a wider range of barrier situations globally, may greatly extend the application of this cost-effective tool.

Stocking Ctenopharyngodon idella (grass carp) for aquatic weed control into a 1.92 ha lake (Parkinsons Lake, 37°19'S, 174°41'E) altered the size and abundance of two species of small native fish, Retropinna retropinna (smelt) and Gobiomorphus cotidianus (bully). The response of the two species differed. R. retropinna recruitment apparently failed during the ‘high impact’ phase of C. idella stocking (44 fish ha‐1), when all aquatic weeds were removed. Immature fish disappeared and samples comprised 100% large females. G. cotidianus also increased in size, however, condition improved and the sex ratio did not alter markedly. Diet of both species switched from small zooplankton to Chironomus sp. Following reduction in C. idella stocking density, some return of population meristics toward prestocking values occurred. Loss of the weed bed habitat, water quality deterioration, and increased predation were considered the major environmental impact factors during the period when these changes occurred. T...

Landlocked sockeye salmon (Oncorhynchus nerka), ranging in fork length (FL) from 105 to 313 mm, were captured in fine‐mesh gill nets set in the limnetic zone of the Waitaki hydro lakes (44° 30′ S, 170° 10’ E) in the South Island, New Zealand. A total of 443 stomachs was examined and the frequency of occurrence, volume and weight of prey items calculated. In the Ahuriri Arm of Lake Benmore the principal food (54% by weight) was zooplankton (Boeckella dilatata) whereas in the Haldon Arm of Lake Benmore it was larval and juvenile common bullies (Gobiomorphus cotidi‐anus) (73% by volume). In Lake Waitaki in winter, salmon had eaten insects (43% by volume) with smaller amounts of snails (Potamopyrgus antipo‐darum, 23%) and bullies (24%). In Lake Ohau adult insects may be an important food. There were also variations in diet with season and fish size. The stomachs of 147 brown trout (Salmo trutta) and 181 rainbow trout (S. gairdnerii) caught in the same gill nets were also examined. In contrast to sock...

Observations were made of the response to water velocity for upstream migrating juveniles of 5 diadromous native fishes (Anguilla auslralis, Galaxiasmaculatus,Galaxiasfasciatus,Retropinna relropinna, Gobiomorphus colidianus). Swimming performance within a hydraulic flume was measured and observations made of the behavioural adaptions of some species to swim through high water velocities. Timed swimming at known water velocities allowed estimation of critical velocities for fish passage. For juvenile fishes (30–80 mm total length), velocities below 0.3 m s‐1 should allow unrestricted passage over obstacles less than 15 m in length. Water velocities below 0.25 m s‐1 may be necessary for obstacles over 15m. Field observations of Mugil cephalus corresponded with limited flume data, suggesting this species is a less vigorous swimmer: water velocities below 0.15 m s‐1 would allow its passage over obstacles less than 5 m in length whereas longer obstacles, without resting areas of static water, may requ...

1. A new genus of trematode (family Allocre-adiidae) from the intestine of freshwater eels is described, and named Stegodexamene anguillae.2. The genus is related to Aephnidiogenes, Lepidapedon and Neophasis, but differs significantly from each of them.3. The life cycle followed is from the adult in Anguilla dieffenbachii to the redia in Potamopyrgus antipodum (fresh-water gastropod). The cercaria encysts in the eloetrid fish Gobiomorphus gobioides.4. Progenetic production of eggs and spermatozoa occurs in the metacercariae.5. Metacercarial excretory spherules are composed of calcium carbonate.

Summary Indigenous freshwater fishes of the Chatham Islands include Geotria australis, Anguilla australis schmidti, A. dieffenbachi, Retropinna retropinna, R. chathamensis, Galaxias argenteus, G. fasciatus, G. attenuatus, G. brevipinnis, and Gobiomorphus huttoni. Their habitats are described and attempts at introducing trout are discussed.

Two new lepocreadiid digeneans, Tetracerasta blepta, gen. sp. nov., and Stegodexamene callista, sp. nov., are described from the intestine of the long-finned freshwater eel, Anguilla reinhardtii, in the Brisbane River, Queensland, and from the Australian bass, Macquaria novemaculeata, in the Richmond River in New South Wales. Their life cycles have been elucidated and completed in the laboratory, by means of uninfected hosts. Both lepocreadiid species use the prosobranch gastropod, Posticobia brazieri, as their first intermediate host. Cercariae of T. blepta penetrate and encyst in the pharyngeal muscle, external muscle, and viscera of fishes in the genera Gobiomorphus and Hypseleotris, and in several species of tree frog tadpoles. The cercariae of S. callista are often eaten or accidentally inhaled by several small fishes, including Retropinna, Craterocephalus, Pseudomugiland Ambasszs, and encyst in the pharyngeal muscle and viscera. All developmental stages are described and illustrated.

Twenty-nine stomachs of the large black shag (Phalacrocorax carbo (Linn.)) and 61 of the white-throated or little pied shag (P. brevirostris (Gould)) from the Rotorua-Taupo area were examined. Techniques used to determine the state of digestion and the identification of otoliths are discussed. Stomach content analyses showed that the food of lake-feeding shags in July consisted almost entirely of fish and freshwater crayfish. Bullies (Gobiomorphus sp.) were the most important food fish. Salmonid fish were found in one stomach (P. carbo).