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  • 1
    Electronic Resource
    Electronic Resource
    Thermal adaptation of Arctic charr: experimental studies of growth in eleven charr populations from Sweden, Norway and Britain (2005)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 50 (2005), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Experimental growth data for Arctic charr (Salvelinus alpinus L.), all fed on excess rations, from 11 European watercourses between 54 and 70°N were analysed and fitted to a new general growth model for fish. The model was validated by comparing its predictions with the growth rate of charr in the wild.2. Growth performance varied among populations, mainly because of variation in the maximum growth potential, whereas the thermal response curves were similar. The estimated lower and upper temperatures for growth varied between −1.7 to 5.3 and 20.8–23.2 °C, respectively, while maximum growth occurred between 14.4 and 17.2 °C.3. There was no geographical or climatic trend in growth performance among populations and therefore no indication of thermal adaptation. The growth potential of charr from different populations correlated positively with fish body length at maturity and maximum weight in the wild. Charr from populations including large piscivorous fish had higher growth rates under standardised conditions than those from populations feeding on zoobenthos or zooplankton. Therefore, the adaptive variation in growth potential was related to life-history characteristics and diet, rather than to thermal conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.2004.01326.x
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  • 2
    Electronic Resource
    Electronic Resource
    Functional models for growth and food consumption of Atlantic salmon parr, Salmo salar, from a Norwegian river (2001)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 46 (2001), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. The chief objectives were to analyse and model experimental data for maximum growth and food consumption of Atlantic salmon parr (Salmo salar) collected from a cold glacier fed river in western Norway. The growth and feeding models were also applied to groups of Atlantic salmon growing and feeding at rates below the maximum. The growth models were validated by comparing their predictions with observed growth in the river supplying the experimental fish. 
2. Two different models were fitted, one originally developed for British salmon and the other based on a model for bacterial growth. Both gave estimates for optimum temperature for growth at 18–19 °C, somewhat higher than for Atlantic salmon from Britain. Higher optimal temperature for growth in salmon from a cold Norwegian river than from British rivers does not concur with predictions from the thermal adaptation hypothesis. 
3. Model parameter estimates differed among growth groups in that the lower critical temperature for growth increased from fast to slow growing individuals. In contrast to findings for brown trout (Salmo trutta), the optimum temperature for growth did not decrease with decreasing levels of food consumption. 
4. A new and simple model showed that food consumption (expressed in energy terms) peaked at 19.5–19.8 °C, which is similar to the optimal temperature for growth. Feeding began at a temperature 1.5 °C below the lower temperature for growth and ended about 1 °C above the maximum temperature for growth. Model parameter estimates for consumption differed among growth groups in a manner similar to the growth models. Maximum consumption was lower for Atlantic salmon than for brown trout, except at temperatures above 18 °C. 
5. By combining the growth and food consumption models, growth efficiency was estimated and reached a maximum at about 14 °C for fast growing individuals, increasing to nearly 17 °C for slow growing ones, although it was lower overall for the latter group. Efficiency also declined with increasing fish size. Growth efficiency was generally higher for Atlantic salmon than for brown trout, particularly at high temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.2001.00631.x
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  • 3
    Electronic Resource
    Electronic Resource
    Performance of juvenile brown trout exposed to fluctuating water level and temperature (2004)
    Oxford, UK; Malden, USA : Blackwell Science Ltd
    Journal of fish biology 65 (2004), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Individual daily food intake, mass-specific growth rate and growth efficiency in groups of juvenile brown trout Salmo trutta were compared in tank experiments with three water level regimes (fluctuating, stable high and low water levels) and two temperature regimes (fluctuating between 10 and 14° C and constant 14° C) to simulate events during hydropeaking in regulated rivers. Fish exposed to high stable water level showed higher food intake and growth rate, and higher or similar growth efficiency than fish exposed to fluctuating or stable low water level. Both groups of slow-growing and fast-growing individuals fed less and grew slower at stable low and fluctuating water level than at stable high water level. Furthermore, growth and growth efficiency were lower in brown trout exposed to stable low water level and fluctuating temperature, particularly for groups of fish with slow growth. Temperature did not have any effect at high water level. For groups of fast-growing fish, there was no difference in growth efficiency between treatments. It is concluded that fluctuating water level and temperature have a potentially detrimental effect on growth in juvenile brown trout and effects are more severe in slow- than fast-growing fish.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.0022-1112.2004.00463.x
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  • 4
    Electronic Resource
    Electronic Resource
    Growth-rate variation in brown trout in small neighbouring streams: evidence for density-dependence? (2002)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 61 (2002), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The within- and among-population variation in individual growth rate of brown trout Salmo trutta L. was studied in five small neighbouring streams (seven isolated populations) within a distance of 70 km in east Norway. Observed growth rate was only weakly correlated with predicted maximum growth rate based on laboratory models, and there was a significant interaction with site. A generalized linear model showed that growth rate was positively correlated with temperature, but also that growth rate decreased as the summer season progressed. This might indicate either a seasonal decline in food availability or appetite, or a change in energy allocation strategy. Growth rate decreased with increasing fish age, probably as an effect of sexual maturation of older fish, and differential allocation of protein and lipid among different size-groups of brown trout. After adjusting for variation in temperature, season, and fish mass, there was still significant among-site variation in growth rate. A significant part of this variation was due to variation in brown trout density and the presence or absence of Alpine bullhead Cottus poecilopus. Growth rate decreased with increasing brown trout density, and was lower in the presence than in the absence of Alpine bullhead after correcting for variation in brown trout density. This last result may indicate the presence of interspecific competition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.2002.tb02494.x
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of Water Chemistry and Habitat on the Density of Young Brown Trout Salmo trutta in Acidic Streams (1999)
    Springer
    Water, air & soil pollution 112 (1999), S. 85-106 
    Details
    ISSN: 1573-2932
    Keywords: acidification ; Brown trout ; calcium ; density ; juveniles ; streams
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract We examined the relationship between young brown trout ( Salmo trutta) density in lake tributaries, and water chemistry and habitat variables. The study was carried out during the autumn in three acidic, softwater river systems in western and southwestern Norway; Gaular and Vikedal (1987–1993) and Bjerkreim (1988–1993). The streams had mean calcium concentrations of 0.35 mg L-1 (Gaular), 0.52 mg L-1 (Vikedal) and 0.84 mg L-1 (Bjerkreim). The concentration of inorganic Al was generally low, with mean values of 8.40 (Gaular), 22.22 (Vikedal) and 43.36 μg L-1 (Bjerkreim). In multiple regressions that involved different water chemistry variables, brown trout density correlated best with calcium concentration and with a combination of calcium and pH; the Ca2+:H+ ratio. In Vikedal and Gaular, calcium explained 51 and 57%, respectively, of the variability in brown trout densities. Althoug alkalinity exhibited the best correlation with brown trout density in Bjerkreim ( r2=0.33), it was similar to that of the model that included all major ions plus pH. The Ca2+:H+ ratio had a larger effect for variability in brown trout density in Gaular (r2=0.66) than calcium alone. In Vikedal and Bjerkreim, the Ca2+:H+ ratio also correlated with brown trout density, but considerably less than in Gaular. The predictive power of habitat variables was much lower than that of water chemistry; the single most important factors were altitude in Gaular (r2=0.22), mean water temperature in Vikedal (r2=0.11) and depth SD (index of heterogeneity) in Bjerkreim (r2=0.07). Models that included both habitat and water chemistry variables showed that the density of young brown trout was predicted primarily by calcium concentrations in Gaular (r2=0.75) and Vikedal (r2=0.54), as opposed to pH in Bjerkreim (r2=0.25). Habitat had low effect in all three river systems (r2=0.01–0.04). The final model explained 86, 68 and 32%, respectively, of the variability in brown trout density in the three catchments. Thus, water chemistry variables seem to be factors that limit the density of young brown trout in acidic softwater streams.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005068404832
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