Fatty acid ethyl esters as an alternative oil in aquafeeds: Effects on growth performance and nutrient digestibility in European seabass juveniles

Fish oil (FO) has been the main commercially available source of eicosapentaenoic (EPA) and docosahexaenoic (DHA) fatty acids for aquafeeds. Fatty acid ethyl esters (FAEE) oil is a byproduct of omega-3 production for human consumption. It is still rich in EPA but relatively poor in DHA, and its utilization in aquafeeds is still poorly studied. This study assessed the impact of FAEE oil dietary inclusion on European seabass (ESB; Dicentrarchus labrax ) juveniles' growth performance, feed utilization, nutrient digestibility, body composition, and muscle fatty acid (FA) profile. For that purpose, four isoproteic (48%) and isolipidic (16%) diets were formulated with different FO, rapeseed, and FAEE oil (FO/RO/FAEE) ratios: D1, control diet (78/22/0); D2 (22/78/0); D3 (22/56/22); and D4 (0/22/78). The growth trial was conducted for 88 days at 23 °C (ESB weight:62 g). Digestibility of the diets was assessed in a separate trial (ESB weight:161 g). Growth performance, feed utilization, survival rates, and body composition were unaffected by the dietary inclusion of FAEE oil. The apparent digestibility of dry matter, protein, lipid, and energy, and the activities of amylase, lipase, and total proteases were similar between dietary treatments. Muscle DHA and total n-3 LC-PUFA were lower, while the n-6/n-3 ratio was increased in fish fed D2, D3, and D4 compared to D1. EPA content was identical in fish fed diets D1 and D4. Adenylate degradation indices used as muscle quality indicators were not affected by dietary treatment. Overall, FAEE oil completely replaced FO in ESB juveniles' diets without affecting growth performance or feed utilization. However, dietary DHA supplementation may be necessary to maintain the nutritional quality of the muscle.