Effets d’une alimentation végétale sur la biosynthèse des acides gras et le métabolisme du bar européen (Dicentrarchus labrax)

In the context of the fish farming industry needing to substitute the animal food (meal and oil) by vegetable ingredients, the main objective of this thesis was to study the long-term effects of a diet exclusively composed by plant products on the metabolism of the european sea bass (Dicentrarchus labrax) and more particularly, on its capacity to biosynthesis the Highly Unsaturated Fatty Acids (HUFA) from the PolyUnsaturated Fatty acids (PUFA) brought by this vegetal diet. Our transcriptomic approaches showed that the use of a plant food disrupted the lipids metabolism (cholesterol and fatty acids) and the energy metabolism (carbohydrates, amino acids) in the liver, but also affected other physiological processes such as the immune system. In spite of the regulation of the fatty acids metabolism in fish when fed with the vegetal diet, the european sea bass is not able to convert effectively the AGPI brought by this food into HUFA. In particular, this low conversion rate affects the fish quality for the consumer by reducing the HUFA content in the muscle. Such an incapacity to bioconvert high quantities of HUFA could be link to the low enzymatic activity of the delta-6-desaturase (FADS2) involved in the HUFA metabolic pathway. Our proteomic and transcriptomic approaches dedicated to the characterization of this enzyme showed that the low level of the FADS2 activity measured in the liver and the intestine of sea bass fed with a plant food is not the consequence of a poor-functionality of the enzyme, but rather, a post-transcriptionnal regulation. By acting as a metabolic bottleneck, the activity of this enzyme reduced the HUFA synthesis what also affects the physiological functions modulated by these fatty acids such as the immune function.