Abstract
Ongoing rapid domestication of Atlantic salmon implies that individuals are subjected to evolutionarily novel stressors encountered under conditions of artificial rearing, requiring new levels and directions of flexibility in physiological and behavioural coping mechanisms. Phenotypic plasticity to environmental changes is particularly evident at early life stages. We investigated the performance of salmon, previously subjected to an unpredictable chronic stress (UCS) treatment at an early age (10 month old parr), over several months and life stages. The UCS fish showed overall higher specific growth rates compared with unstressed controls after smoltification, a particularly challenging life stage, and after seawater transfer. Furthermore, subjecting fish to acute stress at the end of the experiment, we found that UCS groups had an overall lower hypothalamic catecholaminergic and brain stem serotonergic response to stress compared with control groups. In addition, serotonergic activity was negatively correlated with final growth rates, which implies that serotonin responsive individuals have growth disadvantages. Altogether, our results may imply that a subdued monoaminergic response in stressful farming environments may be beneficial, because in such situations individuals may be able to reallocate energy from stress responses into other life processes, such as growth.
Highlights
Stressful stimuli, over prolonged periods of time, have often been associated with maladaptive behaviour and disease [1]
Fish groups did not differ in body weight (t28 = −1.39, p = 0.18; mean: 63 ± 1 and 63 ± 2 for unpredictable chronic stress (UCS) and control, respectively) or condition (t28 = −1.53, p = 0.14; mean: 1.15 ± 0.01 and 1.18 ± 0.01 for UCS and control, respectively) at the start of the experiment
We show evidence that Atlantic salmon subjected to a stressful regime during early life display a mitigated hypothalamic catecholaminergic (CA) and brain stem serotonergic response to acute stress later in life, compared to non-treated fish
Summary
Over prolonged periods of time, have often been associated with maladaptive behaviour and disease [1]. Phenotypic plasticity may be defined as, the individual’s capacity to change its phenotype in response to environmental cues in order to increase its fitness in a given environment [2]. In this context, stressful situations will affect individuals depending on how they are programmed to cope with their environment and this programming may be genetic or acquired during early life stages [3,4,5]. Atlantic salmon (Salmo salar) strains have gone through a rapid and intense domestication in recent years This involves subjecting salmon to a series of aquaculture environment challenges, which represent stressors that do not necessarily resemble those occurring in nature [8]. In agreement with reports from the mammalian literature, it may be possible to prepare individuals to cope with challenges encountered in artificial rearing through environmental programming during early life stages [9,10]
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