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

## TL;DR

This study shows that a diet rich in omega-3 fatty acids improves cognitive and behavioral traits in young brown trout, helping them catch larger prey in natural-like environments.

## Contribution

The study demonstrates the ecological relevance of dietary n-3 LC-PUFA on cognitive and behavioral traits in wild brown trout populations.

## Key findings

- Trout on a high n-3 LC-PUFA diet showed better cognitive performance and lower boldness.
- They were more capable of capturing and consuming larger prey in semi-natural environments.
- Behavioral and cognitive differences were observed between populations, independent of lake or river origin.

## 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.

With this study, we tested the role of dietary n‐3 LC PUFA on behaviour and cognition of brown trout
Salmo trutta
from different lacustrine and riverine populations. Secondly, we tested the ecological relevance of these traits evaluating fish resource acquisition in a semi‐natural stream mesocosm through the inspection of stomach contents. We found that fish fed a high n‐3 LC PUFA diet had better cognitive performance, lower boldness and better capacities on catching larger prey. Behavioural and cognitive traits differed between population independently of whether trout were from lake or river.