• development;
  • fish;
  • heritability;
  • personality;
  • plasticity;
  • teleost

This work examined behavioural responses in yolk-sac rainbow trout Oncorhynchus mykiss larvae originating from strains selected for high (HR) or low (LR) plasma cortisol response to a standardized stressor. The results showed that yolk-sac larvae originating from the HR strain were more sensitive to environmental stressors, in that they showed a shorter reaction time to low oxygen levels. Previous studies on adult and juvenile individuals from these strains demonstrated a number of correlated physiological and behavioural differences. In yolk-sac larvae, growth and development depended mainly on internal factors, which suggest that at least some aspects of stress-coping styles are inherent to the individual, before factors such as social experience or variable access to food resources could modify behavioural strategy.