Neochanna Apoda Research Articles

Metabolism drives distribution and abundance in extremophile fish.

Differences in population density between species of varying size are frequently attributed to metabolic rates which are assumed to scale with body size with a slope of 0.75. This assumption is often criticised on the grounds that 0.75 scaling of metabolic rate with body size is not universal and can vary significantly depending on species and life-history. However, few studies have investigated how interspecific variation in metabolic scaling relationships affects population density in different sized species. Here we predict inter-specific differences in metabolism from niche requirements, thereby allowing metabolic predictions of species distribution and abundance at fine spatial scales. Due to the differences in energetic efficiency required along harsh-benign gradients, an extremophile fish (brown mudfish, Neochanna apoda) living in harsh environments had slower metabolism, and thus higher population densities, compared to a fish species (banded kōkopu, Galaxias fasciatus) in physiologically more benign habitats. Interspecific differences in the intercepts for the relationship between body and density disappeared when species mass-specific metabolic rates, rather than body sizes, were used to predict density, implying population energy use was equivalent between mudfish and kōkopu. Nevertheless, despite significant interspecific differences in the slope of the metabolic scaling relationships, mudfish and kōkopu had a common slope for the relationship between body size and population density. These results support underlying logic of energetic equivalence between different size species implicit in metabolic theory. However, the precise slope of metabolic scaling relationships, which is the subject of much debate, may not be a reliable indicator of population density as expected under metabolic theory.

Hiding in the swamp: new capillariid nematode parasitizing New Zealand brown mudfish.

The extent of New Zealand's freshwater fish-parasite diversity has yet to be fully revealed, with host-parasite relationships still to be described from nearly half the known fish community. While advances in the number of fish species examined and parasite taxa described are being made, some parasite groups, such as nematodes, remain poorly understood. In the present study we combined morphological and molecular analyses to characterize a capillariid nematode found infecting the swim bladder of the brown mudfish Neochanna apoda, an endemic New Zealand fish from peat-swamp-forests. Morphologically, the studied nematodes are distinct from other Capillariinae taxa by the features of the male posterior end, namely the shape of the bursa lobes, and shape of spicule distal end. Male specimens were classified into three different types according to differences in the shape of the bursa lobes at the posterior end, but only one was successfully characterized molecularly. Molecular analysis indicated that the studied capillariid is distinct from other genera. However, inferences about the phylogenetic position of the capillariid reported here will remain uncertain, due to the limited number of Capillariinae taxa characterized molecularly. The discovery of this new capillariid, which atypically infects the swim bladder of its host, which itself inhabits a very unique ecosystem, underlines the very interesting evolutionary history of this parasite, which for now will remain unresolved.

Drought survival is a threshold function of habitat sizeand population density in a fish metapopulation.

Because smaller habitats dry more frequently and severely during droughts, habitat size is likely a key driver of survival in populations during climate change and associated increased extreme drought frequency. Here, we show that survival in populations during droughts is a threshold function of habitat size driven by an interaction with population density in metapopulations of the forest pool dwelling fish, Neochanna apoda. A mark-recapture study involving 830N.apoda individuals during a one-in-seventy-year extreme drought revealed that survival during droughts was high for populations occupying pools deeper than 139mm, but declined steeply in shallower pools. This threshold was caused by an interaction between increasing population density and drought magnitude associated with decreasing habitat size, which acted synergistically to increase physiological stress and mortality. This confirmed two long-held hypotheses, firstly concerning the interactive role of population density and physiological stress, herein driven by habitat size, and secondly, the occurrence of drought survival thresholds. Our results demonstrate how survival in populations during droughts will depend strongly on habitat size and highlight that minimum habitat size thresholds will likely be required to maximize survival as the frequency and intensity of droughts are projected to increase as a result of global climate change.

Trap-shyness subsidence is a threshold function of mark-recapture interval in brown mudfish Neochanna apoda populations.

The influence of capture interval on trap shyness, and temperature, rainfall and drought on capture probability (p) in 827 brown mudfish Neochanna apoda was quantified using mark-recapture models. In particular, it was hypothesized that the loss of trapping memory in marked N. apoda would lead to a capture-interval threshold required to minimize trap shyness. Neochanna apoda trap shyness approximated a threshold response to capture interval, declining rapidly with increasing capture intervals up to 16.5 days, after which p remained constant. Tests for detecting trap-dependent capture probability in Cormack-Jolly-Seber models failed to detect trap shyness in N. apoda capture histories with capture intervals averaging 16 days. This confirmed the applicability of the 16 day capture-interval threshold for mark-recapture studies. Instead, N. apoda p was positively influenced by water temperature and rainfall during capture. These results imply that a threshold capture interval is required to minimize the trade-off between the competing assumptions of population closure and p homogeneity between capture occasions in closed mark-recapture models. Moreover, environmental factors that influence behaviour could potentially confound abundance indices, and consequently abundance trends should be interpreted with caution in the face of long-term climate change, such as with global warming.

Multiple environmental stressors increase the realised niche breadth of a forest‐dwelling fish

Understanding the determinants of species' niche breadth is important due to the negative relationship between niche breadth and extinction probability. Species tolerant to extremely harsh abiotic conditions (e.g. low pH or hypoxia) often have relatively small realised niches due to a trade‐off between abiotic and biotic stress tolerance, and are therefore particularly vulnerable to extinction. We hypothesised that tolerance to multiple extreme conditions (e.g. low pH, hypoxia and drought) in brown mudfish Neochanna apoda, would increase their realised niche breadth because each extreme would provide additive refuge against a dominant species, the banded kokopu Galaxias fasciatus. Fish distributions were surveyed in 65 peat‐swamp‐forest streams and pools in New Zealand, which varied in dissolved oxygen, acidity and hydroperiod. Mudfish distribution was extremely patchy, and almost completely allopatric with kokopu. Allopatry was driven mainly by pool hydroperiod; mudfish occupied 88 percent of temporary pools due to their tolerance of habitat drying, whereas kokopu were absent from temporary pools. Within permanent pools, mudfish occurrence was negatively related to pool oxygen and pH, whereas kokopu occurrence was positively related to these conditions. Pool conditions were independently distributed in the landscape, suggesting that each abiotic stressor offered additive refuge for mudfish from kokopu predation/competition. Consequently, the mudfish realised niche breadth depended on the number of abiotic factors driving their allopatry with kokopu. Given the widespread negative relationships between niche breadth and species extinction probabilities, our results indicate that tolerance to multiple stressors may play an important role in insuring species persistence against the multiple drivers of global environmental change.

Physiological and biochemical strategies for withstanding emersion in two galaxiid fishes

The galaxiid fishes of the Southern hemisphere display variable tolerance to aerial exposure. Brown mudfish (Neochanna apoda), for example, pseudoaestivate, inhabiting moist soil for months at a time, whereas inanga (Galaxias maculatus) emerse under unfavourable water conditions, but only for periods of a few hours. This study sought to identify the physiological and biochemical strategies that determine emersion tolerance in these species. Nitrogenous waste excretion was measured before and after an experimental emersion period (14days for mudfish, 6h for inanga). Both species showed significantly elevated ammonia “washout” upon return to water, but no increase in plasma or muscle ammonia. Post-emersion urea levels were elevated in plasma and muscle in both fish, however the extent of the accumulation did not indicate significant de novo urea production. This was supported by the lack of carbamoyl phosphate synthetase activity in tissues. Consequently, mudfish metabolism was examined to determine whether changes in parameters such as oxygen consumption, carbon dioxide excretion, and/or altered metabolic costs (represented by the key ionoregulatory enzyme Na+, K+-ATPase; NKA) could explain emersion tolerance. Oxygen consumption rates, already very low in immersed mudfish, were largely maintained over the course of emersion. Carbon dioxide excretion decreased during emersion, and a small, but significant, decrease in NKA was noted. These data suggest that the extended emersion capacity of mudfish may result from a generally low metabolic rate that is maintained throughout aerial exposure via cutaneous gas exchange, and which limits the production of potentially toxic nitrogenous waste.

A new species of mudfish, Neochanna (Teleostei: Galaxiidae), from northern New Zealand

A new species of mudfish, Neochanna, is described from Northland Neochanna heleios n sp is known from only three ephemeral wetland sites on the Kerikeri volcanic plateau and is abundant only at the type locality The new species has a head resembling that of the brown mudfish, Neochanna apoda, and a caudal region resembling that of the black mudfish, Neochanna diversus It can be distinguished from all Neochanna species in having a reduced number of principal caudal fin rays (13 or less) Morphometric and meristic comparisons with N apoda and N diversus are provided

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

Distribution and post-glacial dispersal of freshwater fishes in South Westland, New Zealand

Abstract Sixteen native and two introduced species of fishes were recorded in a survey of South Westland fresh waters. All of the native species are diadromous, except for the brown mudfish (Neochanna apoda), which was recorded only north ofWaiho River. The number of fish species recorded in South Westland was lower than the number known from the Buller River catchment or North Westland, but greater than in western Fiordland. It is suggested that during the Otiran glaciation, freshwater fishes on the west coast of the South Island were restricted to the Buller River catchment and parts of North Westland. Diadromous fishes have recolonised South Westland readily from those northern refugia, but non-diadromous fishes appear to have been reinvading the area more slowly. N. apoda has adaptations which have allowed it to recolonise more rapidly than most non-diadromous species.

Suspected terrestrial deposition of eggs by Neochanna apoda Günther (Pisces: S almoniformes: Galaxiidae)*

A description is given of the finding of eggs of Neochanna apoda distributed above the waterline in an aquarium. Actual spawning has not been observed. but the probability of terrestrial deposition of eggs by the fish in its natural enrivonment is recognized, and the possible ways in which this may be accomplished are discussed.

The Canterbury mudfish, Galaxias burrowsius Phillipps, a vanishing species

Summary Examination of available samples and of ecological knowledge of Galaxias burrowsius Phillipps (Galaxiidae) suggests that this species is confined to the Canterbury Plains and is now nearly extinct. Possible reasons for its decline are analysed and it is suggested that this decline may have started nearly 1,000 years ago with the changes in the climate‐vegetation pattern. It has been hastened by the recent drastic transformation of the environment by European settlers. Distribution and habitats of two other New Zealand mudfishes, Neochanna apoda and N. diversus (Galaxiidae) are related to those of G. burrowsius

Notes on the presence of the brown mudfish(Neochanna apodagünther) on the west coast of the south Island of New Zealand

Summary Two visits to the West Coast revealed that Neochanna apoda Giinther is present in six clearly defined types of habitat examined between Oparara and Whataroa. The location of habitats varied from heavily forested country to open pakihi bog, between sea level and 200 m. A Neochanna apoda habitat was generally uninhabited by any other species of fish; occasionally short‐finned eels (Anguilla australis) and, once, banded kokopu (Galaxias fasciatus) were present. An association with freshwater crayfish (Paranephrops planifrons) was often noted. Neochanna apoda was found in all stages of development from fry to adults over 150 mm in length, and all size ranges were present in some places.