Effect of different dietary protein-energy ratio on growth, feed utilization, body composition and haematological indices of European sea bass, Dicentrarchus labrax fingerlings

Abstract

This study was conducted to investigate the effect three dietary protein energy ratio on growth performance, feed utilization and haematological indices of European sea bass Dicentrarchus labrax fingerlings culture in net enclosures (hapa, 30 m-3 each) for 60 days. The experimental treatments were assigned in triplicate. Three test diets were formulated to contain three different protein levels (450, 500, and 550 g kg-1 diet) and three lipid levels (174, 160 and 150 g kg-1 diet) to provided three different dietary protein: energy ratio (P: E ratio: 20 , 23 and 25 mg CP kJ-1 GE g-1, P:E21, P:E23 and P:E25, respectively). A total of 180 European sea bass, Dicentrarchus labrax with an average initial body weight of 13.0 ± 0.5 g fish-1 were randomly distributed into nine net enclosures measuring (3 × 8 ×1.25m each) at a stocking density of 20 fish per net enclosure. Over the 60-days feeding period, growth, feed utilization efficiency and survival (%) of D. labrax fingerlings was improved significantly (P>0.05) with increasing dietary protein energy ratio up to P:E23compared to P:E25 diets. The same trend was observed for the best feed conversion ratio (FCR). No statistical difference (P ≥ 0.05) was observed for the influence of dietary protein energy ratio on whole body proximate analysis of fish except for protein which recorded the highest values for fish fed P:E23 diet. Mean red blood cell counts (RBCs), mean white blood cell counts (WBCs), hematocrit (Hct), hemoglobin (Hb), total plasma protein, total plasma globulin, plasma sodium chloride and glucose of D. labrax fingerlings significantly (P ≥ 0.05) increased for fish fed the diets P:E25 compared to other experimental treatments. An opposite trend was observed for plasma cortisol, albumin, plasma aspartate aminotransferase (AST) and alanine aminotransferase (ALT) values. The obtained findings revealed that, the diet containing 500 g kg-1 protein and 160 g kg-1 lipid with dietary P: E ratio of 23 mg CP kJ GE g-1 is recommended to stimulate growth performance, nutrients utilization efficiency and haematological indices of D. labrax fingerlings