N-3 long chain polyunsaturated fatty acids (n-3 LC PUFA or omega 3), and in particular docosahexaenoic acid (DHA) and ecosapentaenoic acid (EPA), are poorly synthetized de novo by marine fish, but are nevertheless necessary for maintaining their metabolic and physiological performances. Consequently, fish must find them in their food. However, the production of these lipid compounds by marine microalgae (main producers) is predicted to decrease with global changes, and will consequently decrease their availability for fish. The aim of this study was to experimentally determine the effects of a n-3 LC PUFA deficient diet on the escape performance, determinant parameter in predator-prey relationships, of Chelon auratus, a microphytobenthos grazer of high ecological importance. Fish were fed either a standard or a deficient n-3 LC PUFA diet during two months. Different variables related to the escape response (latency, responsiveness, initial direction, response duration, distance travelled, maximum acceleration and velocity, turning rate) were characterized on the fish at the end of the nutritional conditioning period. Results showed that growth rate and escape responses variables were similar in both dietary groups. However, several escape response variables (e.g. duration, maximum velocity and acceleration, turning rate), were highly correlated with fish n-3 LC PUFA content in brain or muscle, and these correlations were tissue-specific. Also, high DHA/EPA ratio in brain membrane would increase maximum velocity and turning rate. Our results suggest that a modification of the n-3 LC PUFA fish tissue composition in the context of global change would impact predator-prey relationships.