Abstract
Life experiences in the rearing environment shape the neural and behavioral plasticity of animals. In fish stocking practices, the hatchery environment is relatively stimulus-deprived and does not optimally prepare fish for release into the wild. While the behavioral differences between wild and hatchery-reared fish have been examined to some extent, few studies have compared neurobiological characteristics between wild and hatchery-reared individuals. Here, we compare the expression of immediate early gene cfos and neuroplasticity marker brain-derived neurotrophic factor (bdnf) in telencephalic subregions associated with processing of stimuli in wild and hatchery-reared Atlantic salmon at basal and 30 min post (acute) stress conditions. Using in situ hybridization, we found that the expression level of these markers is highly specific per neuronal region and affected by both the origin of the fish, and exposure to acute stress. Expression of cfos was increased by stress in all brain regions and cfos was more highly expressed in the Dlv (functional equivalent to the mammalian hippocampus) of hatchery-reared compared to wild fish. Expression of bdnf was higher overall in hatchery fish, while acute stress upregulated bdnf in the Dm (functional equivalent to the mammalian amygdala) of wild, but not hatchery individuals. Our findings demonstrate that the hatchery environment affects neuroplasticity and neural activation in brain regions that are important for learning processes and stress reactivity, providing a neuronal foundation for the behavioral differences observed between wild and hatchery-reared fish.
Highlights
Wild Atlantic salmon (Salmo salar L.) populations are declining worldwide (Parrish et al, 1998)
The hatchery environment provides optimal conditions for growth, which leads to higher growth rates and larger body size at time of release for hatchery-reared fish compared to wild fish of the same age (Jonsson and Jonsson, 2009)
Transcript abundance of bdnf increased in response to acute stress in the dorsal part of the dorsomedial pallium (Dmd) of wild fish, but not in that of hatchery-reared individuals
Summary
Wild Atlantic salmon (Salmo salar L.) populations are declining worldwide (Parrish et al, 1998). Hatchery Rearing Affects Salmon Neuroplasticity to support declining population numbers are frequently employed, such as the annual release of millions of hatcheryreared salmon into rivers worldwide through stocking programs (e.g., Palmé et al, 2012; Maynard and Trial, 2013). After release in the wild, stocked salmon often show reduced stomach fullness (Johnson et al, 1996) or ingestion of indigestible particles such as small rocks and plant material (Munakata et al, 2000) Behavioral deficits such as these contribute to lower post-release survival rates of stocked fish compared to their wild conspecifics (Johnson et al, 1996; Jonsson and Jonsson, 2009; Thorstad et al, 2011), raising both financial and ethical concerns for current stocking practices
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