Individual Growth Variability in Farmed Atlantic Salmon (Salmo salar L.): The Role of Social Interactions

Cubitt, Kathleen Fiona (2002) Individual Growth Variability in Farmed Atlantic Salmon (Salmo salar L.): The Role of Social Interactions. PhD thesis, University of Glasgow.

Abstract

This thesis examines the development and persistence of size variation in Atlantic salmon (Salmo salar). A series of linked studies characterised individuals displaying marked differences in growth trajectories. These studies investigated size variation from a behavioural perspective and provided information that may be applied to the commercial production of Atlantic salmon. Chapter 2. Tracked the development of size variation in semi commercial conditions. A six month long study allowed the identification of sub groups offish displaying distinct growth trajectories. These sub groups were apparent as lower, upper and main modes in the weight distribution of each population. Chapter 3. Investigated behavioural differences in three sub-groups of varying sizes. This revealed that lower mode fish were behaviourally distinct from small fish in the main mode and from large fish (the largest fish in the main mode and the upper mode fish combined). Lower mode fish fed at different times of the day from large fish and occupied different areas of the tank. In addition, the proportion of large fish feeding was greater when competition for food was increased, and lower when competition for food was decreased. Lower mode fish displayed the opposite pattern; a greater proportion fed when competition for food was decreased. These results suggest that lower mode fish were excluded from feeding at the same times as large fish either because of direct competition or due to social interactions. Chapter 4. Demonstrated a biochemical technique to recreate previous social status. This technique provided strong evidence that social hierarchies can occur in relatively large groups at high densities. The results from this study suggest the occurrence of a long-term linear hierarchy, with consistently large fish remaining dominant and a small group of profoundly subordinate individuals. However, it is likely that there was also a continually changing group of fish that became dominant for short periods. Chapter 5. Investigated the capacity of non-growing fish to grow. Non-growing fish from the long-term study on the development of size variation (Chapter 2) provided the opportunity to relate the effects of season and of larger individuals on the performance of non-growing fish. These previously non-growing individuals grew after the summer solstice, but those in the absence of larger fish exhibited a faster and greater recovery than those in the presence of larger fish. Chapter 6. Investigated the concept of intrinsic competitive ability. The occurrence of differential growth rates in initially tightly graded populations (Chapter 2) suggested that particular individuals were predisposed to perform well. Thus, the growth of good performers were compared with size-matched poor performers. This revealed that previous performance (which may be confounded by previous winning experience) provided an initial, short term growth advantage. Chapter 7. General discussion Brings together the findings and concepts of the previous chapters and discusses the implications that these findings have for commercial farming of Atlantic salmon.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: Felicity Huntingford
• Keywords: Evolution & development, Aquatic sciences
• Date of Award: 2002
• Depositing User: Enlighten Team
• Unique ID: glathesis:2002-75750
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 18:17
• Last Modified: 19 Nov 2019 18:17
• URI: https://theses.gla.ac.uk/id/eprint/75750