Variation in behaviour and growth of common sole : genetic and environmental influences

Common sole (Solea solea) has a high potential for commercial aquaculture because of its consumer popularity and high market values in Europe. However, a major economic constraint for the culture of sole is its slow and variable growth. The aim of this thesis was to investigate: 1) the importance of (non-) feeding behaviour of sole in relation to variation in growth; 2) the effect of (social and physical) environmental factors on behaviour, growth and the relation between them; 3) the existence of GE interaction regarding growth. Feeding consistency, swimming activity in the tank, and boldness during (novel environment and light avoidance) behavioural tests explained variation in feed intake and thereby growth of individually housed sole. For communally housed sole, behavioural factors derived from individual behavioural tests and sex also explained variation in growth. The motivation to bury was negatively related to growth, whereas the motivation to explore a novel environment was positively related. Social interactions, both in quality (i.e., size hierarchies) and in quantity (i.e.,stocking density), influenced (non-) feeding behaviour and growth of sole. High stocking density in sole reared without substrate results in more fish-fish interactions, which increases swimming activity, FCR and variation in growth. These conditions seem to induce social stress in sole, which is alleviated when sand is provided. Environmental factors which differ between nature and farming conditions, such as food type, sand and variability of environmental conditions, influenced individual behavioural responses of sole to a novel environment test but did not induce variation in growth. Results suggest that consistent relationships between behaviour and growth develop when fish are reared in stable barren environments but not when fish experience more variable, enriched/natural environments. The role of environmental factors in the relationship between (non)-feeding behaviour and growth was supported by strong genotype by environment interaction for growth of sole reared in a semi-natural or an intensive aquaculture environment. In conclusion, the effect of (non-) feeding behaviour on growth should be taken into account to foster progress in the farming of sole. Environmental factors (i.e., substrate, stocking density) that influence behaviour and growth should be used to optimize culture systems. Future genetic selection strategies should focus more on behavioural characteristics to select sole which will be able to cope and grow best in the different rearing conditions present in commercial aquaculture.