Selective breeding to improve welfare in farmed fish: Modification of the stress response in rainbow trout (Oncorhynchus mykiss)

Intensive rearing of fish presents the challenge of minimising production cost without compromising the health and well-being of the stock. Most farmed fish species, (with the exception of carp) are just a few generations removed from the wild-type and consequently many relatively benign aspects of the aquaculture environment are perceived as stressors by fish. Although the neuroendocrine stress response is a key element of an animals adaptive repertoire, inappropriate activation of the response leads to poor growth, reproductive dysfunction and immunosuppression. One strategy that has been investigated to address this is to selectively breed for reduced stress responsiveness - by reducing the magnitude of response to conditions that elicit a stress response, the longer-term cumulative effects of stress on the performance and well-being of the population will be reduced. The trait associated with stress responsiveness that is most accessible to directed selection is the magnitude of the plasma cortisol response. Cortisol is known to be a causal agent in most of the adverse effects of stress in fish. This presentation will outline the results of a selective breeding programme to ameliorate stress in fish, including the finding that neuroendocrine differences arising from selection for either high or low activity of the hypothalamic-pituitary axis during stress are accompanied by a bimodality in behavioural characteristics and cognitive attributes. These suggest that the two selected lines exemplify two distinct combinations of physiological and behavioural strategies for dealing with stressful circumstances akin to the proactive and reactive coping strategies observed in mammals.