Clarias gariepinus juveniles Clarias gariepinus dissection URBE FISH PROTEINS NOT LIPIDS ARE THE MAJOR NUTRIENTS LIMITING THE REPLACEMENT OF FISH MEAL BY VEGETABLE INGREDIENTS IN CATFISH NUTRITION Sourabié1.2, F. Geay1, S.N.M. Mandiki1, T. Sene1, A. Toguyeni2 and P. Kestemont1 1Natural Resources and Environmental Sciences Research and Studies Laboratory (LERNSE), Institute of Rural Development (IDR), Polytechnic University of Bobo-Dioulasso, Burkina Faso 2University of Namur, Research Unit in Environmental and Evolutionary Biology, Rue de Bruxelles, 61, B-5000 Namur, Belgium. Aboubacar.sourabie@unamur.be INTRODUCTION Substitution of fish products in fish nutrition is currently an important research challenge. Previous studies have shown that the African catfish (Clarias gariepinus) is a very interesting aquaculture species able to valorize high proportions of vegetable ingredients without detrimental effects on growth (Ng et al., 2002, Nyina-Wamwiza et al., 2007). However, the respective effects of replacement of fish proteins or lipids by vegetable ingredients are not yet described. The objectives of our study were: to determine the growth response and lipid metabolism including desaturase (FADS2) and elongase (ELOVL5) gene expressions of catfish submitted to a total replacement of fish protein versus fish lipid compounds by vegetable ingredients; to outline the effectiveness of proteins and lipids in catfish nutrition MATERIALS AND METHODS 360 catfish juveniles (14g IBW) distributed to 12- RAS tanks of 30 fish per tank. Three replicate tanks per dietary treatment. Four isonitrogenous (45%), isolipidic (10%) and isoenergetic (17.5 kJ.g-1) diets: 1. Control diet (FPHP), containing fish meal and fish oil (Menhaden oil); 2. Diet 2 (FPHV) containing fish meal and vegetable oils; 3. Diet 3 (FVHP) containing vegetable meal and fish oil; 4. Diet 4 (FVHV) containing vegetable meals and vegetable oils. Vegetable meals were a mixture of soybean cake and lupine meal, while vegetable oils were composed of linseed and cottonseed oils. Output variables after 7 weeks of feeding: 1. Growth rate (SGR), feed conversion ratio (FCR), protein efficiency (TEP) 2. Total lipids and fatty acid composition in muscle, liver and intestine from 5 fish per tank 3. Desaturation and elongation gene expressions of FADS2 and ELOVL5 Clarias gariepinus juveniles Clarias gariepinus dissection RESULTS Fish oil replacement did not affect SGR (FPFH vs FPVH), while significant lower values were observed for fish meal replacement whatever the oil source (fig. 1a). No significant differences in SGR between fish fed vegetable (FVHP vs FVHV) proteins whatever the quality of lipid sources (fig. 1a). FCR and TEP values were similar to those of SGR (fig. 1b and fig. 1c). Values for elongase (ELOVL5) and desaturase (FADS2) gene expressions were the highest in fish receiving fish meal and vegetable oil (FPHV, fig. 2a and fig. 2b), and no differences between fish fed other diets.  effective utilization of vegetable oils if associated to fish proteins. No clear effect of replacement of fish proteins or lipids on fatty acid composition: - lower ARA content for phospholipid class of fish fed vegetable oil (FPHV and FVHV) (Tab.), - vs higher EPA and DHA levels in fish fed fish ingredients than those in other diets. CONCLUSIONS The available results revealed that fish proteins are the limiting nutrients in the substitution of fish products by vegetable ingredients. The study also demonstrated that catfish are able to bioconvert efficiently fatty acids from vegetable ingredients, especially when associated with fish proteins. Acknowledgments: The study was supported by ARES (Académie de Recherche et d’Enseignement supérieur) Belgium Aquaculture Europe 2015, Rotterdam, Netherlands, October 20-23, 2015