Fishes require n-3 long chain polyunsaturated fatty acids (n-3 LC PUFA) to develop and maintain their physiological functions (e.g. growth, immunity, reproduction, locomotion). While marine fishes are one of the main vectors of n-3 LC PUFA from the aquatic environment to humans, they are known to be weakly able to synthesize n-3 LC PUFA de novo from precursors. Their richness in n-3 LC PUFA actually almost entirely relies on the n-3 LC PUFA production at the basis of marine trophic webs (microalgae) and transfer through the trophic chain. Global changes (e.g. temperature, oxygen, pH) are suggested to affect n-3 LC PUFA production by primary producers by influencing their physiology and assemblage. This would reduce the availability of these molecules for fishes, alter the lipid composition of their cell membranes, with potential consequences on their physiological performances. Our studies aim to test experimentally the effect of n-3 LC PUFA availability on the physiological performances of the golden grey mullet. We showed that a deficiency impairs growth, swimming performance, and metabolic rates. When combined with warmer environment, this deficiency lead to a greater alteration of the cell membranes, growth, metabolism and cardiac function. However, a depleted diet also increased swimming efficiency, which should improve the fish capacity to forage, and compensate for the reduction in growth and metabolism. These results could have wider implications for population dynamics and ecosystem functioning, and impact on the n-3 LC PUFA availability for humans, both through changes in fish stocks and their n-3 LC PUFA quality.