Abstract
•The growth rate and feed efficiency of European sea bass were enhanced by dietary nucleotides.•Diets supplemented with nucleotides exhibited normal blood biochemical features.•The intestine, liver, and spleen histology showed improved features in fish fed dietary nucleotides.•Dietary nucleotides at 500 mg/kg is the optimum level for better performances of European seabass.
Nucleotides (NT), as a modern feed additive, are effective in many vital functions of cultured aquatic organisms. An experiment was performed to evaluate the effects of dietary nucleotides on the growth performance, carcass composition, liver enzymatic profile, liver, intestine, and spleen histology in European sea bass, Dicentrarchus labrax (initial weight 29.56 ± 0.083 g/fish). Four isonitrogenous (46 % crude protein) and isolipidic (16 % crude lipid) experimental diets were supplemented with different levels of nucleotides, representing N0, N500, N1000, and N1500 treatments, respectively. Each diet was fed to three net enclosures (experimental net cage: 1 × 1 × 1 m) with 0.5 m3 water volume, and each net enclosure contained eight fish. The fish were fed to satiation for 56 days. The results showed significant (P < 0.05) differences in growth performance and feed utilization indices in favor of N500 among all the treatments (P < 0.05). Seabass fed N0 and N1500 had the significantly lowest results. No significant (P < 0.05) differences in survival were detected. Fish fed diets supplemented with nucleotides exhibited significantly lower values of alkaline phosphatase activity (ALP), aspartate aminotransferase activity (AST), alanine aminotransferase activity (ALT), and bilirubin (BIL) compared with the control. The intestine, liver, and spleen histology showed the best development in N500 fed group fish compared with the other treatment, mainly N0 and N1500. In conclusion, the present experiment showed that 500 mg/kg of dietary nucleotides is the optimum level for the best growth performance, health condition, and digestive organs development of D. labrax.