Gilthead sea bream juveniles of 135 g average body weight were fed for 120 days a fish oil-based commercial diet (CTRL) or one of two experimental isonitrogenous and isolipidic low fat (LF) fish meal-based diets differing only by the lipid source, in order to evaluate the efficacy of beef tallow (BT) as an ingredient in aquafeeds. Both experimental feeds were formulated with 60 g/kg of BT; the LFBTFO diet also contained 35 g/kg of fish oil (FO) whereas a blend of BT and vegetable oils (VO) completely replaced FO in the LFBTVO diet. No differences in growth and feed efficiency were found between fish fed the LFBTFO diet and the CTRL group whereas fish fed the diet devoid of FO (LFBTVO) presented the poorest growth indicators and the lowest feed and protein efficiencies. The use of LF feeds contributed to maintain the hepatosomatic index and the proportion of triacylglycerols (TAG) in muscle and brain in spite of the dietary replacement of FO. Flesh from fish fed the LFBTFO diet supplied the same absolute amount of EPA + DHA than that of fish fed the CTRL diet, whereas a reduction of approximately 45% was registered when fish were deprived of FO.
Practical applications: High proportions of BT can effectively be used as a valuable alternative to partially substitute FO in diets for gilthead sea bream juveniles without significantly affecting fish performance and health while promoting a limited impact on its health benefits for human consumption. The decline in the inclusion of marine ingredients in aquafeeds could actively contribute to the sustainability and profitability of the marine aquaculture industry.