Fish welfare assessment through brain function: Impacts of environmental stress on brain plasticity and behaviour

Developing reliable measures of fish welfare is a priority within Norway and the EU. Although fish welfare definitions vary, a key aim is to provide environments that minimize stressors that impact health and the animal?s mental function. In mammals, prol onged stress can affect brain function to such a degree that specific regions structurally deteriorate. Our goal is to develop assays to identify specific brain alterations related to specific stressors. While brief mild stress can enhance learning and me mory, in mammals, chronic or severe stress impairs these processes, decreasing coping ability. These effects are linked to a reduction in neural plasticity in the hippocampus and amygdala, brain regions associated with learning, memory, reward processes a nd aggressive behaviour. Homologous regions are also found in the fish brain, namely the lateral (Dl) and medial (Dm) telencephalon. Knowledge on the effects of stress on neural plasticity in fish is scarce. The present proposal aims to establish the mole cular and functional relationship between environmental stress, neural plasticity, and learning and memory behaviours in salmon. We will focus on chronic mild stress (CMS), in the form of hyperoxia, acid-aluminium (acid-Al), and constant light (LL), as th is type of stress is the most difficult to detect using classical methods, and is also the most relevant in aquaculture. We will include a test group implanted with cortisol to determine which CMS effects are cortisol mediated. Following behavioural tests (learning, memory and coping abilities), the fish brains will be sampled for the quantification and localisation of key neural plasticity and stress markers. These studies will provide the basis so that we can employ gene expression fingerprinting throug h microarray analysis to identify gene specific biomarkers that can be used to evaluate conditions that may impact learning and memory and consequently adaptation and coping ability.