Relationships between environmental conditions, energetic strategies and performance in juvenile Atlantic salmon, Salmo salar

• Main Author: Reid, Donald
• Format: Thesis
• Language: English
• Published: 2012
• Subjects: QH301 Biology; QL Zoology; Atlantic salmon; Salmo salar
• Online Access: http://theses.gla.ac.uk/3122/; http://theses.gla.ac.uk/3122/1/2012reidphd.pdf.pdf; https://eleanor.lib.gla.ac.uk/record=b2911843

Energy is the fundamental currency of life that drives organismal growth and development. Energy requirements vary greatly between species but also within species due to differences in physiology, behaviour and life history. The consequence of this variation is of great interest to ecologists, as it is potentially a trait upon which natural selection can act. One of the main components of an organism’s energy budget is its baseline level of metabolism, hereafter termed its standard metabolic rate (SMR). It has been shown in several species of salmonid fish that a high standard metabolic rate correlates with dominance, aggression and boldness. This competitive advantage has been shown to result in higher growth over conspecifics in simple lab environments, but the ecological consequences are less clear. This thesis examined the performance of contrasting metabolic strategies across a range of environmental conditions to ascertain the ecological consequences of SMR variation. Experiments also investigated the relationships between SMR, food intake and absorption efficiency to help relate energetic strategies to performance. The effects of environment on the outcome of different energetic strategies were profound. Higher population densities increased intraspecific competition for preferable feeding territories, but fish with a higher SMR tended to be the best competitors and so were most likely to get a preferred territory (Chapter 2). However, for a given quality of feeding territory, whether relatively good or poor, lower SMR individuals grew best due to their lower energy requirements. The benefit to high SMR fish of being able to secure better territories was diminished under less predictable feeding conditions, and disappeared under a structurally complex habitat, resulting in these fish having no performance advantage over fish with a lower SMR (Chapter 3). These high SMR individuals performed poorly in the presence of low densities of a heterospecific competitor, being subject to a disproportionate proportion of the aggression from a more dominant species (brown trout, Chapter 4). At higher densities of trout, intraspecific interactions appeared much more important for both species, resulting in the salmon with the highest SMR exhibiting the fastest growth. These three chapters demonstrate that environmental conditions, both abiotic and biotic, have great consequences for the success of different energetic strategies. The consequences of metabolic strategy on physiology proved just as interesting. High SMR individuals expended more energy when digesting a given size of meal but reduced the duration of this specific dynamic action (SDA, the rise in metabolism associated with processing and digesting a meal) response (Chapter 5). This suggested that their digestion was more rapid than that of low SMR fish, but this did not lead to a higher rate of food consumption (Chapter 5) nor did they sacrifice absorption efficiency (Chapter 6). This thesis demonstrates that the performance of fish with alternative energetic strategies is dependent on the prevailing environmental conditions, which helps explain the persistence of variation in SMR within populations.