A semantic model for overall welfare assessment of Atlantic salmon reared in sea cages is presented. The model, called SWIM 1.0, is designed to enable fish farmers to make a formal and standardized assessment of fish welfare using a set of selected welfare indicators. In order to cover all welfare relevant aspects from the animals’ point of view and to create a science‐based tool we first identified the known welfare needs of Atlantic salmon in sea cages and searched the literature for feasible welfare indicators. The framework of semantic modelling was used to perform a structured literature review and an evaluation of each indicator. The selected indicators were water temperature, salinity, oxygen saturation, water current, stocking density, lighting, disturbance, daily mortality rate, appetite, sea lice infestation ratio, condition factor, emaciation state, vertebral deformation, maturation stage, smoltification state, fin condition and skin condition. Selection criteria for the indicators were that they should be practical and measureable on the farm, that each indicator could be divided into levels from good to poor welfare backed up by relevant scientific literature. To estimate each indicator’s relative impact on welfare, all the indicators were weighted based on their respective literature reviews and according to weighting factors defined as part of the semantic modelling framework. This was ultimately amalgamated into an overall model that calculates welfare indexes for salmon in sea cages. More importantly, the model identifies how each indicator contributes (negatively and positively) to the overall index and hence which welfare needs are compromised or fulfilled.

Despite the use of fish models to study human mental disorders and dysfunctions, knowledge of regional telencephalic responses in nonmammalian vertebrates expressing alternative stress coping styles is poor. As perception of salient stimuli associated with stress coping in mammals is mainly under forebrain limbic control, we tested regionspecific forebrain neural (i.e. mRNA abundance and monoamine neurochemistry) and endocrine responses under basal and acute stress conditions for previously characterised proactive and reactive Atlantic salmon. Reactive fish showed a higher degree of the neurogenesis marker proliferating cell nuclear antigen ( pcna) and dopamine activity under basal conditions in the proposed hippocampus homologue (Dl) and higher post-stress plasma cortisol levels. Proactive fish displayed higher post-stress serotonergic signalling (i.e. higher serotonergic activity and expression of the 5-HT 1A receptor) in the proposed amygdala homologue (Dm), increased expression of the neuroplasticity marker brain-derived neurotropic factor (bdnf ) in both Dl and the lateral septum homologue (Vv), as well as increased expression of the corticotropin releasing factor 1 (crf 1 ) receptor in the Dl, in line with active coping neuro-profiles reported in the mammalian literature. We present novel evidence of proposed functional equivalences in the fish forebrain with mammalian limbic structures.

The present study aimed to compare effects of increasing chronic stress load on the stress response of European seabass (Dicentrarchus labrax) and gilthead seabream (Sparus aurata) to identify neuroendocrine functions that regulate this response. Fish were left undisturbed (controls) or exposed to three levels of chronic stress for 3 weeks and then subjected to an acute stress test (ACT). Chronic stress impeded growth and decreased feed consumption in seabass, not in seabream. In seabass basal cortisol levels are high and increase with stress load; the response to a subsequent ACT decreases with increasing (earlier) load. Basal cortisol levels in seabream increase with the stress load, whereas the ACT induced a similar response in all groups. In seabass and seabream plasma α-MSH levels and brain stem serotonergic activity and turnover were similar and not affected by chronic stress. Species-specific molecular neuro-regional differences were seen. In-situ hybridization analysis of the early immediate gene cfos in the preoptic area showed ACT-activation in seabream; in seabass the expression level was not affected by ACT and seems constitutively high. In seabream, expression levels of telencephalic crf, crfbp, gr1, and mr were downregulated; the seabass hypothalamic preoptic area showed increased expression of crf and gr1, and decreased expression of mr, and this increased the gr1/mr ratio considerably. We substantiate species-specific physiological differences to stress coping between seabream and seabass at an endocrine and neuroendocrine molecular level. Seabass appear less resilient to stress, which we conclude from high basal activities of stress-related parameters and poor, or absent, responses to ACT. This comparative study reveals important aquaculture, husbandry, and welfare implications for the rearing of these species.

The evolutionary background for cognition and awareness is currently under ardent scrutiny. Poikilothermic vertebrates such as teleost fishes are capable of classical conditioning and have long-term memories, but it remains unknown to what degree such capabilities are associated with affective states. Here, we investigate whether the concept of frustration may apply to Atlantic salmon. In mammals, this paradigm comprises the omission of an expected reward (OER), which elicits behavioural and physiological coping responses (e.g. aggression and stress reactions). Six groups with 200 fish in each were conditioned to associate a flashing light (CS) with feeding. Conditioning over 22 days led to a change from aversion to attraction to the CS. Subsequently, 3 groups served as control, and 3 groups were subjected to an OER paradigm for 9 days, in which the expected food reward was delayed for 30 min during two out of three daily meals. Compared to controls, OER groups displayed higher levels of aggression and more heterogeneous growth rates, indicating a more pronounced social hierarchy. Cortisol levels did, however, not differ between treatments and both groups responded similarly to acute stress. These results indicate that teleost fishes, like mammals, respond aggressively to OER. The capacity to respond behaviourally to frustrating conditions thus likely reflects an adaptive response to environmental unpredictability, which has been conserved throughout vertebrate evolution.