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Whiterod N.S.,Murray Darling Freshwater Research Center | Whiterod N.S.,Charles Sturt University
Ecology of Freshwater Fish

This study documented the swimming capacity of a large ambush predator, Murray cod Maccullochella peelii, endemic to the Murray-Darling Basin, Australia. It was evident that the species is a swimming generalist, maintaining moderate ability across all aspects of the swimming capacity parameters that were investigated. For instance, the species was capable of prolonged swimming performance (critical swimming speed, Ucrit: absolute, 0.26-0.60 m·s-1, relative, 1.15-2.20 BL s-1) that was inferior to active fish species, but comparable with other ambush predators. The species had low energetic demands, maintaining a low mass-specific standard (21.3-140.3 mg·h-1 kg-1) and maximum active metabolic rate (75.5-563.8 mg·h-1 kg-1), which lead to a small scope for activity (maximum active metabolic rate-standard metabolic rate; 1.4-5.9). They were reasonably efficient swimmers (absolute and relative optimal swimming speed, 0.17-0.61 m·s-1 and 0.77-1.93 BL·s-1, respectively) and capable of repeat bouts of prolonged performance (recovery ratio = 0.99). Allometric changes in aspects of swimming capacity were realised with body mass, whereas broad swimming capacity was maintained across a wide range of temperatures. The swimming capacity demonstrated by M. peelii reflects a sit-and-wait foraging strategy that seeks to conserve energy characteristic of ambush predators, but with distinct features (e.g., lack of fast-start ability) that may reflect their evolution in some of the world's most hydrologically and thermally variable rivers. © 2012 John Wiley & Sons A/S. Source

Vilizzi L.,Murray Darling Freshwater Research Center
Fundamental and Applied Limnology

Temporal variability in flow is central to the functioning of river ecosystems, with current conceptual models emphasising the importance of flow events, namely overbank flood pulses and in-channel flow pulses, in enhancing riverine fish production. However, whilst the benefits of flood pulses have been widely documented, there is an overall dearth of information with regard to the role of flow pulses in enhancing fish spawning and recruitment. To test the validity of applicable conceptual models of floodplain fish production in response to alternating low-flow and flow-pulse years in the absence of a flood pulse, fish larvae were sampled every three to five weeks from 2002 to 2007 in an anabranch system of the highly-regulated and semi-arid lower Murray River (southeastern Australia). Small-bodied native fish (mainly, un-specked hardyhead, carp gudgeon, flathead gudgeon and Australian smelt) spawned successfully in every year irrespective of hydrological conditions, with Australian smelt being particularly abundant in two of the three low-flow years following a flow-pulse event. However, spawning in the majority of these small-bodied species was enhanced by the two flow pulses. On the contrary, large-bodied silver perch and golden perch only spawned during one of the two spring flow pulses, emphasising the importance of both timing and duration of a flow pulse along with its coupling with temperature. The findings of the present study support recent views that a combination of conceptual models of floodplain fish production is likely to apply in temperate to semi-arid floodplain rivers. Management measures aimed at the benefit of native fish communities should account for both flow and flood pulses through the release of environmental water, and this should be supported by long-term studies able to span the components of a river's flow history. © 2012 E. Schweizerbart'sche Verlagsbuchhandlung. Source

Copp G.H.,Center for Environment | Copp G.H.,Bournemouth University | Vilizzi L.,Murray Darling Freshwater Research Center | Gozlan R.E.,Murray Darling Freshwater Research Center
Aquatic Conservation: Marine and Freshwater Ecosystems

1. The contamination of fish consignments (for stocking or aquaculture) is a major pathway by which non-native organisms, including fish, are introduced to new areas. One of the best examples of this is the topmouth gudgeon Pseudorasbora parva, which was accidentally imported into Romania and then throughout Europe in consignments of Asian carp species. 2. The introduction and spread of topmouth gudgeon in the UK has been linked to imports and movements of the ornamental variety (golden orfe) of ide Leuciscus idus. To examine this hypothesis, relationships between authorized movements of both native and non-native fish species (in particular ide) and the occurrence in England of topmouth gudgeon were tested at the 10 × 10 km scale. 3. Topmouth gudgeon occurrence in the wild was significantly correlated with the trajectories of movements of ornamental fish species (ide/orfe, sunbleak Leucaspius delineatus) as well as a few non-ornamental fish species (European catfish Silurus glanis, Atlantic salmon Salmo salar and grass carp Ctenopharyngodon idella). 4. These results highlight the mechanism by which non-native fish species disperse from the point of first introduction, and especially that movements of fish within the country represent an important mechanism for accidental introductions of non-native species. © Crown copyright 2010. Source

Vilizzi L.,Murray Darling Freshwater Research Center | Copp G.H.,Salmon and Freshwater Team | Copp G.H.,Trent University | Britton J.R.,Bournemouth University
Knowledge and Management of Aquatic Ecosystems

Suspected of being in decline, the European barbel Barbus barbus population of the River Lee, a heavily-modified river in South East England, has been the subject of investigations to identify factors associated with perceived population decreases. Population surveys between 1995 and 1999 captured a total of 912 individuals, and standard length (SL) frequency analyses between years suggested that the population decline was not related to juvenile recruitment but rather to a recruitment bottleneck in fish 300-340 mm SL. This bottleneck probably results from insufficient available habitat suitable to this size class. Of the sampled fish, scales were removed from 764 and were used in a scale ageing exercise among three researchers. Analyses of their independent age estimates revealed variable interpretations, which arose from uncertainties relating to the difficulty of analysing scale patterns from relatively large, slow-growing fish. Nevertheless, error was within published acceptable margins, and age estimates revealed B. barbus in the river to age 10 years, lower than in many UK rivers. The SL-at-age growth curve was characterised by very fast growth in the initial years of life. Thus, the causal factors in the decline of this B. barbus population appear to have been in the adult life-stage habitat and were likely related to the loss of longitudinal connectivity, mainly due to the presence of water retention structures. River and aquatic ecosystem remediation strategies should therefore focus on enhancing longitudinal connectivity in conjunction with the ongoing improvement of water quality and ecosystem integrity. © ONEMA, 2013. Source

Whiterod N.,Murray Darling Freshwater Research Center | Sherman B.,CSIRO
River Research and Applications

The 60-km-long pool created by the Mildura weir exhibits pronounced physical, chemical and biological gradients along its length. As the river deepens and widens downstream along the weir pool, the flow velocity decreases and the potential for thermal stratification (intensity and duration of stratification) increases. Most nutrient concentrations (TN, NOx, FRP) as well as the euphotic depth increased in the downstream direction whereas TP and turbidity decreased. The increase in bioavailable nutrients co-occurred with an increase in electrical conductivity suggesting the presence of relatively more saline groundwater inflows to the weir pool. Throughout the summer (12 December 2003-18 March 2004), with the exception of 8days, the water column throughout the weir pool mixed completely on a diurnal basis in the deeper sections and was continuously mixed in the shallower upstream sections. This mixing substantially reduced the mean irradiance experienced by the phytoplankton near the weir. Maximum cyanobacteria concentrations were observed in the mid-weir pool where the range of conditions was most suitable. Diatom abundance increased along the most downstream 20km of the pool where the water column was deeper and slower flowing yet still mixed completely on a diurnal basis. Peaks in cyanobacteria biomass are not expected in the lower weir pool until lower discharges promote persistent thermal stratification and increase the mean irradiance in the surface mixed layer. © 2011 John Wiley & Sons, Ltd. Source

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