Physiological and metabolic responses of Asian seabass ( Lates calcarifer ) to complete dietary fish oil replacement with beef tallow, Schizochytrium sp., or their blends

Physiological and metabolic responses of Asian seabass (Lates calcarifer) to complete dietary fish oil replacement with beef tallow, Schizochytrium sp., or their blends Fish oil (FO) is an important lipid source for aquafeeds; however, concerns regarding its limited availability have intensified interest in alternative lipid sources. This study evaluated the effects of replacing FO with blends of beef tallow (BT) and algal oil (AO) on growth performance, feed utilisation, muscle fatty acid composition, lipid metabolism, and antioxidant status in juvenile Asian seabass (Lates calcarifer). Fish were fed six experimental diets containing only FO in the control diet (FO100) or varying proportions of BT and AO (BT100, BT75:AO25, BT50:AO50, BT25:AO75, and AO100) for eight weeks. No dietary effects on the growth performance and somatic indices of the fish were found. The inclusion of AO, particularly in the BT75:AO25 diet, kept long-chain polyunsaturated fatty acid and n–3 fatty acid levels similar to the control group. Fish fed the BT75:AO25 also exhibited greater superoxide dismutase activity and lower malondialdehyde levels than the control group, indicating improved antioxidant status. In addition, acid phosphatase and alkaline phosphatase activities were enhanced in fish fed the BT75:AO25 diet. Overall, the maintenance of muscle LC-PUFAs, together with satisfactory growth performance and enhanced antioxidant capacity, supports the use of the BT75:AO25 blend as a sustainable alternative to FO in juvenile Asian seabass diets.