Individual Variations and Coping Style

By current definition, animal welfare depends on the subjective experience of cognitive and emotional processes that are engendered as individuals succeed or fail in coping with a dynamically changing environment. A functional and evolutionary approach to emotion holds that adaptive qualities such as duration, severity, controllability, and predictability of stressful stimuli determine whether a particular event or outcome is experienced as rewarding or adverse. For instance, stress-induced behavioral inhibition can be seen as an adaptive strategy during chronic, unpredictable, or uncontrollable conditions that do not merit successful active coping. In teleost fishes, such behavior can be taken to indicate a negative welfare status, since it co-occurs with reduced neural plasticity and neuroendocrine alterations akin to brain remodeling seen in depression-like states in mammals. Active responses such as aggression and active avoidance are on the other hand likely to be adaptive when stressors are mild, predictable, and of short duration. Such conditions, albeit leading to acute activation of physiological stress responses, does not necessarily impair welfare. Thus, individual variation in the threshold for when a challenge becomes inhibiting rather than stimulatory is likely key to the subjective experience of welfare in a given situation. Thresholds for employing active (proactive) and passive (reactive) responses are, however, individually variable, and complex gene–environment interactions affects the occurrence and stability of welfare relevant trait correlations. In this chapter, we will review how key components of a stress coping style (i.e., behavior, physiology, neuroendocrinology, neuronal plasticity, and immunity) are subject to great individual and heritable variation, and further how such specific trait characteristics can influence the welfare of fish. A practical outcome for applied studies in aquaculture is that if one aims to understand and measure welfare in the context of individual variation in coping ability, relevant indicators of central nervous system function must somehow be included. The robustness of available markers of neural plasticity and their sensitivity to stress exposure is not fully resolved, but impaired welfare status is most often recognizable by characteristic behaviors such as reduced activity and feeding, and reduced ability to respond to additional stressors.