Academic literature on the topic 'Galaxias olidus'

The introduced salmonid Oncorhynchus mykiss was eradicated by use of the piscicide rotenone from a section of small montane stream upstream of an impassable barrier. Recolonization of the stream both above and below the barrier by the native Galaxias olidus was monitored annually for four successive years. Following trout eradication, G. olidus recolonized the trout-free stream section above the barrier but was never detected below the barrier where trout still occurred. Initial colonization was by juvenile G. olidus but a successful breeding population had established three years after trout eradication. The implications of the use of barriers and targeted eradication programmes are discussed for the management of small, threatened fish species.

The introduced salmonid Oncorhynchus mykiss was eradicated by use of the piscicide rotenone from a section of small montane stream upstream of an impassable barrier. Recolonization of the stream both above and below the barrier by the native Galaxias olidus was monitored annually for four successive years. Following trout eradication, G. olidus recolonized the trout-free stream section above the barrier but was never detected below the barrier where trout still occurred. Initial colonization was by juvenile G. olidus but a successful breeding population had established three years after trout eradication. The implications of the use of barriers and targeted eradication programmes are discussed for the management of small, threatened fish species.

Patterns of feeding in the mountain galaxiid (Galaxias olidus) were examined at dawn and dusk during low flow in April and high flow in September in an intermittent stream. During April (low flow), feeding rates were relatively low and aperiodic, whereas in September (high flow), the fish were clearly feeding diurnally at a relatively high rate. These results suggest that feeding in G. olidus in intermittent streams may vary on a daily and seasonal basis, possibly as a consequence of changes in light availability and stream flow. Light determines the ability of fish to find their prey, and seasonal changes in flow may determine the availability of prey (i.e. drifting invertebrates). This pattern suggests that the predatory impact of drift-feeding fish, such as G. olidus, is likely to be considerably less during low-flow periods when drifting invertebrates are not available than during high-flow periods when such prey may be abundant.

South Australia is a large Australian state (~1,000,000 km2) with diverse aquatic habitats spread across temperate to arid environments. The knowledge of freshwater fishes in this jurisdiction has advanced considerably since the last detailed catalogue of native and alien species was published in 2004 owing to significant survey and research effort, spatial analysis of museum data, and incidental records. The updated list includes 60 native and 35 alien species. New additions to the native fauna include cryptic species of Retropinna semoni s.l. (Weber) and Galaxias olidus s.l. (Günther). Two others have been rediscovered after long absences, namely Neochanna cleaveri (Scott) and Mogurnda adspersa (Castelnau). Range extensions are reported for native populations of Galaxias brevipinnis Günther, Leiopotherapon unicolour (Günther), Hypseleotris spp. (hybridogenetic forms) and Philypnodon macrostomus Hoese and Reader. There are five new alien species records (all aquarium species) including Phalloceros caudimaculatus (Hensel), Poecilia reticulata Peters, Xiphophorus hellerii Heckel, Astronotus ocellatus (Agassiz) and Paratilapia polleni Bleeker, with confirmation of Misgurnus anguillicaudatus (Cantor). Other range extensions for alien (exotic or translocated native) species in different drainage divisions (various modes of human-mediated dispersal) include Nematalosa erebi (Günther), Cyprinus carpio Linnaeus, Oncorhynchus mykiss (Walbaum), Salmo salar Linnaeus, Salvelinus fontinalis (Mitchell), Melanotaenia fluviatilis (Castelnau), Atherinosoma microstoma (Günther), Macquaria novemaculeata (Steindachner), Nannoperca australis Günther, Pseudaphritis urvillii (Valenciennes), and Hypseleotris spp. (hybridogenetic forms). New records are a combination of greater available information and new incursions, highlighting the need for ongoing detailed surveys and reporting to detect rare native and alien species.

Through its ability to measure cell DNA content, flow cytometric analysis (FCA) is a technique capable of accurately assessing the position of cells in the cell cycle. Using FCA to measure the proportion of dividing and nondividing cells, an index was created that allows the amount of cell division within larval fish tissues to be quantified. To assess the suitability of the cell division index (CDI) as an indicator of growth and condition in fish larvae, analyses were divided into four parts. These examined the effects of temperature, nutrition, time of day, and geographic location on the CDI of brain tissue from Galaxias olidus larvae. The index was sensitive to, firstly, differences in the brain CDI of larvae reared at 12 and 20°C and, secondly, to significant fluctuations in mean brain CDI from larvae sampled over 24 h. FCA also revealed significant differences in the CDI of starving and fed larvae. Overall, this study indicates that FCA may be suitable as an indicator of growth and condition in both laboratory-reared and wild fish larvae.

Six rivers within the upper Mumbidgee catchment were sampled for larval and juvenile fish. The rivers represented both regulated and unregulated flow regimes and varied widely in size. There was wide variation in the larval fish communities supported by each river, both in terms of the species diversity and total abundance of fish sampled. The highly regulated reach of the Mumbidgee River sampled during this study had the highest numbers of native species and native individuals of any river sampled. In the two rivers selected for further study, the Murmmbidgee and Goodradigbee, there was a high level of inter-annual consistency in the species composition within the reaches sampled, despite considerable change in the temperature and flow regimes of both rivers. This indicates that at least some spawning of those species sampled may occur each year, regardless of environmental conditions. Estimates of the relative abundance of each species sampled changed markedly between years, and it is argued, on the basis of growth information contained in the otoliths, that differential survival of larvae and juveniles was largely responsible for this shift in relative abundance. Otolith microstructure provided information on the date of spawning and early growth patterns of all species sampled in the upper Mumumbidgee catchment. In addition to determining the age and thus 'birth-date' of an individual, the effect of a particular event or series of events has on growth, and subsequent survival, is permanently recorded in the otolith microstructure. This enables accurate back-calculation and correlation to management actions or natural events. No other research tool has this ability to retrospectively assess, on a daily basis, the impacts of management actions on condition and subsequent survival of fish larvae. Species sampled could be separated into three groups based on spawning requirements; those linked with flow, those linked with temperature and generalist species that appear to have river independent cues, such as photoperiod or moon phase. Patterns in growth rate during the early life history stages enabled quantification of the consequences of variation in environmental conditions on the survival and recruitment of various species. Growth was not always highly correlated with water temperature, in fact, for mountain galaxias, high temperatures appear to negatively affect larval condition and subsequent survival. Conversely, carp exhibited a strategy more consistent with common perceptions, with growth and survival increasing with increasing temperature. The study uncovered spawning and growth patterns that were unexpected. Age analysis of western carp gudgeon demonstrated that they had undertaken a mid-winter spawning, when the water temperature in the main channel was far lower than that at which spawning was previously recorded for this species. Redfin perch from the unregulated Goodradigbee River exhibited growth rates exceeding the published upper limits for this and other closely related species. This growth could not be correlated with either temperature or flow, indicating that there are additional factors that dominate growth rates of redfin perch in the Goodradigbee River. The proportion and abundance of native species alone is not necessarily indicative of a 'healthy' or pristine system; some native species may be positively affected by river regulation, at least as juveniles. Comparison of the current larval fish community with likely pre-European fish communities does provide an indication of change to the system. The results of this study suggest that larval fish growth rates can be strongly influenced by environmental conditions, thus providing a powerful tool for monitoring future change and the factors which cause it. This study has demonstrated the value of larval and juvenile fish age and growth information, derived from otolith microstructure techniques, for many aspects of river management. Current river management priorities for which these techniques provide unique information include the determination of environmental flow regimes and the control of undesirable exotic species such as carp.