Dietary Omega‐3 Long‐Chain Polyunsaturated Fatty Acids Can Enhance Ecologically Relevant Cognitive Traits in Juvenile Brown Trout

ABSTRACT Laboratory experiments have demonstrated that dietary intake of omega‐3 long‐chain polyunsaturated fatty acids (n‐3 LC‐PUFA) is beneficial for survival, reproduction and brain development in many vertebrates including fishes, positively affecting their cognitive abilities. However, how n‐3 LC‐PUFA impact fish behaviour and cognition in natural habitats remains unclear. Populations and individuals of the same species often vary in their capacities to synthesise n‐3 LC‐PUFA due to their local adaptations and life‐history trade‐offs. This may affect their sensitivity to dietary intake of these nutrients and, in turn, their cognitive traits and ecological performance. Here, we tested how dietary n‐3 LC‐PUFA affects behavioural and cognitive traits of brown trout Salmo trutta from two lacustrine and three riverine populations. We combined laboratory behavioural tests with experiments in semi‐natural flume mesocosms to see how dietary treatment affects foraging behaviour in a natural environment (i.e., prey size and taxonomic composition in their stomach contents). Trout raised on a high n‐3 LC‐PUFA diet showed less bold behavioural types and better cognitive performance in laboratory tests and capacity to capture and consume larger prey in the flume mesocosm. Additionally, we observed interpopulation differences in behaviour and cognition, although these differences were independent of whether fish were from lakes or river.