Effects of dietary olive pomace (Olea europaea) on zootechnical performance and physiological responses of Nile tilapia (Oreochromis niloticus) juveniles

The effects of increasing dietary inclusion levels of olive pomace (OP) on growth performance, zootechnical indices, body composition, energy metabolism, and lipid peroxidation were evaluated in juvenile Nile tilapia ( Oreochromis niloticus ). Five experimental diets, formulated to be isoproteic (37% crude protein) and isolipidic (9% lipids), included 0% (OP 0 ), 5% (OP 5 ), 10% (OP 10 ), 15% (OP 15 ), and 20% (OP 20 ) OP. Juveniles (0.56 ± 0.11 g) were stocked in 15 tanks (three replicates per treatment) and fed for 54 days. No significant differences were observed in final body weight, weight gain, specific growth rate, feed intake, or survival. However, feed conversion ratio (FCR) improved in OP 5 and OP 10 and was impaired in OP 20 , with similar responses observed for protein efficiency ratio (PER) and condition factor. The viscerosomatic index increased at higher inclusion levels, whereas carcass yield decreased progressively. Higher inclusion levels (15% and 20%) increased moisture and ash content and reduced body protein and lipid levels. Protein and lipid deposition were higher in OP 5 and OP 10 and lower in OP 20 . Hepatic glycogen levels were unaffected, whereas muscle glycogen levels increased in all OP-fed groups. Plasma glucose levels decreased with OP inclusion, whereas hepatic glucose, triglyceride, and cholesterol levels increased at higher inclusion levels. Muscle lipid peroxidation was higher in OP 20 . Regression models for FCR and PER indicated an optimal OP inclusion range of 7.22%-8.55%. Higher inclusion levels impaired feed utilization efficiency and promoted metabolic alterations, and increased muscle lipid peroxidation. Therefore, olive pomace can be included in diets for Nile tilapia juveniles at moderate levels without compromising growth performance.