Effective complete replacement of fish oil by combining poultry and microalgae oils in practical diets for gilthead sea bream (Sparus aurata) fingerlings

Few ingredients allow the complete replacement of fish meals (FM) and fish oils (FO) in aquaculture feeds without affecting fish performance or fillet nutritive value. This is due to the adequate content of essential nutrients, including the n-3 long-chain polyunsaturated fatty acids (n-3 LC PUFA), and the unique high palatability of FM and fish oil. Some microalgae present abundant amounts of these fatty acids, for instance docosahexaenoic acid (DHA). Therefore, the aim of the present study was to evaluate the effect of two different microalgae products, one providing DHA and eicosapentaenoic acid (EPA, 20:5n-3; ED diet), and the other one DHA and n-6 docosapentaenoic acid (DPA, 22:5n-6; DD diet), in combination with poultry oil and rapeseed oil, as total replacers of fish oil, at two different dietary fish meal contents (15 and 7.5%). The effects of these dietary oil combinations on performance, composition and nutritive quality indexes of gilthead sea bream (Sparus aurata) juveniles were studied and compared against a positive control diet (FO) and two negative control diets (PO diets), one for each dietary fish meal content tested, giving in total 7 experimental diets. Both microalgae products in combination with poultry and rapseed oils were able to completely replace fish oil in practical diets with 15% FM without affecting growth performance, utilization of dietary fatty acids or the nutritional quality of fish fillet for the consumer. On the contrary, PO alone was not able to completely replace fish oil and negatively affected fish performance, in relation to an insufficient dietary n-3 LC-PUFA content. A similar decrease in growth performance was also observed with the reduction of the dietary FM content to 7.5%. In conclusion, both oils from microalgae, providing either DHA and EPA or DHA and n-6 DPA, were effective n-3 LC-PUFA sources for sea bream juveniles and allowed complete replacement of fish oil in combination with more cost-effective lipid sources, such as poultry and rapeseed oils.