Inanga Galaxias Maculatus Research Articles

Sensory Biology as a Risk Factor for Invasion Success and Native Fish Decline

AbstractNative freshwater fish populations are among the world's most threatened taxa due to the combined effects of habitat degradation and invasive alien species. Habitat degradation negatively impacts native species, whereas invasive species tend to possess adaptations, such as thermal and salinity tolerance, that are more suited to the degraded environment. Sensory ecology may also be a contributing factor. Most threatened native species are visual feeders, whereas invasive species found in degraded systems often have nonvisual specializations. Behavioral and distributional characteristics of the invasive Western Mosquitofish Gambusia affinis and the New Zealand native Inanga Galaxias maculatus illustrate the potential for sensory biology to influence foraging success, distribution, and species interaction between degraded and clear habitats. Behavioral trials measured the change in feeding rate in clear (0 NTU) and turbid (100 NTU) water over 30 min for Inanga and Western Mosquitofish feeding on brine shrimp Artemia salina nauplii. These experiments showed that Western Mosquitofish maintained similar feeding rates between clear and turbid water, whereas the native species exhibited a marked decline in feeding efficiency in turbid water. Across a strong natural turbidity boundary, the alien species was found to dominate turbid habitat less than 1 m from clear water, where both species were found. Accounting for sensory biology as a potential contributing factor in the establishment of invasive fish species in degraded habitat may help to identify invasive species risk and to shape strategies for rehabilitating native species.

Variable survival across low pH gradients in freshwater fish species.

A series of 14 day experiments was conducted on five common New Zealand fish species (redfin bully Gobiomorphus huttoni, inanga Galaxias maculatus, brown trout Salmo trutta, longfin eel Anguilla dieffenbachii and koaro Galaxias brevipinnis) to assess the effect of pH on survival and changes in body mass. No species survived in water of pH <4 although there was 100% survival of all adults at pH 4.5, G. maculatus larvae were also tested and had high mortality at this pH. Results suggest that adults are tolerant of low-pH waters; however, successful remediation of anthropogenically acidified streams will require an understanding of the susceptibility to low pH on different life cycle stages.

Effect of ramp length and slope on the efficacy of a baffled fish pass

This study evaluated the effect of ramp length and slope on fish passage over baffled ramps with 15° and 30° gradients. Three fish species indigenous to New Zealand were tested: the redfin bully Gobiomorphus huttoni, the common bully Gobiomorphus cotidianus and the inanga Galaxias maculatus with ramp lengths of 3, 4·5 and 6 m. As slope and ramp length increased, passage success rate decreased for G. maculatus and G. cotidianus. At a slope of 15°, both G. maculatus and G. cotidianus could pass all ramp lengths tested with the highest success rate on the 3 m ramp. As the gradient increased to 30°, G. maculatus could only pass the 3 m ramp, and G. cotidianus were incapable of passing any ramp. Gobiomorphus huttoni were the only test species capable of climbing the wetted margin of the ramps. Increasing ramp slope significantly reduced passage success for G. huttoni, but ramp length, up to the maximum used in this study, had no significant influence on successful passage.

The importance of cutaneous gas exchange during aerial and aquatic respiration in galaxiids

The Canterbury mudfish Neochanna burrowsius was found to be a pseudo-aestivating galaxiid with a low metabolic rate and significant cutaneous oxygen uptake (c. 43%) in both air and water. Another galaxiid, inanga Galaxias maculatus, had a higher metabolic rate in both media but the proportion of oxygen uptake met by cutaneous respiration rose significantly from 38 to 63% when the fish were exposed to air. Besides its important role in oxygen uptake, the skin of both species also contributed significantly to excretion of carbon dioxide in air, indicating the critical role of the integument as a respiratory tissue. In air, G. maculatus may increase cutaneous gas exchange to meet metabolic demands owing to the reduced utility of the gills, but as emersed G. maculatus were only able to maintain metabolic rates at c. 67% of that measured in water, this strategy probably only permits short-term survival. By contrast, the low and unchanging metabolic rate in water and air in N. burrowsius is a feature that may facilitate tolerance of long periods of emersion in the desiccating environments they inhabit.

Learning the ropes: mussel spat ropes improve fish and shrimp passage through culverts

Summary Culvert pipes are regularly used around the world for conveying stream flows underground, through embankments or under road crossings. Installation of these features can have significant negative effects on the passage of freshwater biota and potentially exclude many species from large areas of river networks. We investigated the installation of mussel spat ropes as a potentially rapid and cost‐effective tool for improving passage of freshwater biota through culvert pipes where internal barrel conditions impede passage. We assessed passage success for two fish species, juvenile rainbow trout Oncorhynchus mykiss (Walbaum 1972) and adult inanga Galaxias maculatus (Jenyns 1842), and one migratory shrimp, Paratya curvirostris (Heller 1862), through culverts of differing length (3 and 6 m), slope (1·5 and 3°) and flow (0·24 and 0·75 L s−1). We hypothesized that ropes would enhance the passage success of these three species, but success rates would differ between species and trial combinations. Ropes resulted in a reduced water velocity within culvert barrels and significantly improved passage success for all three species. Shrimp benefited most by the presence of ropes, being unable to negotiate any of the pipe combinations in their absence, but exhibiting varying rates of success across all combinations with their presence. Both G. maculatus and O. mykiss were able to negotiate some of the non‐roped pipe combinations, but as the level of difficulty increased, successful passage was only achieved with the ropes present. Synthesis and applications. We conclude that this relatively inexpensive and easy‐to‐install tool has the potential to substantially improve passage for a range of aquatic biota through various culvert scenarios. We consider that ropes would be particularly useful in situations where internal culvert access is difficult and where various culvert parameters (slope, flow, length) result in internal barrel hydraulics that would normally limit or exclude passage of aquatic biota.

Is the Habitation of Acidic-Water Sanctuaries by Galaxiid Fish Facilitated by Natural Organic Matter Modification of Sodium Metabolism?

Acidic waters of New Zealand's West Coast are hypothesized to be a refuge for native galaxiid fish, allowing them to escape predation from acid-sensitive invasive salmonid species. To determine the mechanisms by which galaxiids tolerate low pH, we investigated sodium metabolism in inanga Galaxias maculatus in response to water pH, short-term acclimation to acidic waters, the presence and source of natural organic matter (NOM), and fish life history. Contrary to expectation, inanga were physiologically sensitive to acid exposure, displaying inhibited sodium influx and exacerbated sodium efflux. Short-term (144 h) acclimation to acid did not modify this effect, and NOM did not exert a protective effect on sodium metabolism at low pH. Inanga sourced from naturally acidic West Coast waters did, however, display a sodium influx capacity (J(max)) that was significantly elevated when compared with that of fish collected from neutral waters. All inanga, independent of source, exhibited exceptionally high sodium uptake affinities (18-40 μM) relative to previously studied freshwater teleosts. Although inanga displayed relatively poor physiological tolerance to acidic waters, their high sodium influx affinity coupled with their occupation of near-coastal waters with elevated sodium levels may permit habitation of low-pH freshwaters.

Predation of inanga (Galaxias maculatus) eggs by field mice (Mus musculus)

The common house mouse Mus musculus was observed feeding on the eggs of the indigenous fish, the inanga Galaxias maculatus. This mouse is an introduced species to New Zealand and could potentially be a major predator of the eggs of inanga and other galaxiids that utilise the terrestrial environment for spawning. Further investigation into mice densities and egg predation within known inanga spawning grounds is warranted to determine whether mice are indeed major predators of inanga eggs. If so, whitebait spawning ground management may need to incorporate rodent control measures.

Upstream passage of inanga Galaxias maculatus and redfin bullies Gobiomorphus huttoni over artificial ramps

The effects of surface type and slope on fish passage over artificial ramps were evaluated for two small diadromous fish species native to New Zealand: the redfin bully Gobiomorphus huttoni and adult and juvenile inanga Galaxias maculatus. Surfaces tested include smooth plastic, sand, gravel (limestone chips 5–20 mm), nylon brush and two plastic moulded cores of ground drainage products Cordrain® and Miradrain®. Slopes of 15° (1:3·7), 30° (1:1·7) and 45° (1:1) were assessed. Slope was the greatest factor influencing successful passage, with the lowest gradient tested (15°) providing the highest passage for both fish species. Most ramps at 45° only allowed the passage of redfin bullies, these fish being capable of ‘climbing’ the wetted margin of the ramps. Because of this climbing ability, redfin bullies were not as affected by the ramp surface, as inanga. Nevertheless, the smooth plastic surface, which resulted in the highest water velocities over the ramps, was un‐passable by either species at slopes &gt;15°. Gravel, the nylon brush and the two plastic moulds provided high passage rates for inanga at gradients of 15 and 30°. At a slope of 45°, Miradrain® was the only surface inanga could pass. Overall, Miradrain® produced the most successful passage for both inanga and redfin bullies, but to maximize passage, slope should not be &gt;15° and a wetted margin is essential for climbing species.

Effects of fish size, time‐to‐fatigue and turbulence on swimming performance: a case study of Galaxias maculatus

A simple relationship for the inanga Galaxias maculatus swimming velocity is suggested and tested in low and high turbulence channels. The relationship connects the swimming velocity with fish Reynolds and Froude numbers and can be used in both ecological analysis (e.g. habitat requirements) and management strategies (e.g. fishways design). Contrary to some previous studies and intuition, effects of turbulence on swimming performance appeared to be negligible. The most likely explanation for this result relates to mechanics of fish–turbulence interactions that may be dependent on both the turbulence scales and energy. The data suggest that future studies of turbulence effects on fish behaviour should involve, in addition to turbulence energetics, consideration of fish dimensions in relation to the spectrum of turbulence scales.

Observations on the life history ofDeretrema minutumManter, 1954 (Digenea: Zoogonidae) in freshwater crustacean and fish hosts from Canterbury, New Zealand

Abstract Two new hosts are recorded for Deretrema minutum Manter, 1954 from freshwater habitats at Lake Ellesmere, Canterbury. These are the mysid Tenagotnysis chiltoni Tattersall, 1923 which acts as a second intermediate host and harbours the encysted metacercariae, and the smelt, Retropinna retropinna (Richardson, 1848), which contains adult worms. Adult D. minutum were also found in the inanga Galaxias maculatus Jenyns, 1842. A large proportion of metacercariae within the crustacean host exhibited progenesis which results in the production of numerous eggs. Ovigerous metacercariae were identical with adult D. minutum recovered from the intestine of freshwater fishes from Lake Ellesmere. A description of the metacercaria is given.