A 60-day experiment was conducted to evaluate the effect of dietary fish meal (FM) replacement with poultry by-product meal (PBM) on digestive enzymes, non-specific serum enzyme activity, and serum biochemical parameters of juvenile sobaity sea bream, Sparidentex hasta, weighing 29.27 ± 0.06 g. PBM replaced 0, 15, 25, 35, 45, and 55% of dietary FM in the isoproteic (50%) and isocaloric (21 kJ g-1) experimental diets. The final body weight, percentage weight gain, specific growth rate, and protein efficiency ratio were higher in PBM15, 25, and 35 than in control, PBM45, and 55. Digestive lipase and amylase activity did not differ significantly between the dietary treatments. Significantly lower trypsin and higher chymotrypsin activity were observed at PBM55 and 45, respectively. Digestive alkaline phosphatase (ALP) increased, whereas protein apparent digestibility coefficients (ADC) decreased significantly with increasing levels of PBM above 35%. Hematocrit, hemoglobin, mean corpuscular hemoglobin concentration, serum albumin, globulin, total protein, glucose, urea, uric acid, and aspartate aminotransferase did not show any significant differences between the treatments. Serum ALP, cholesterol, and calcium were higher in PBM diets than in the control diet, whereas an inverse trend was observed in triglyceride. Protein digestibility and trypsin activity and serum biochemical indices suggest that fish meal protein could be reduced up to 45% by the inclusion PBM in the formulated diets for S. hasta juveniles without any adverse effect on its overall performance.
Keywords: Apparent digestibility; Dietary substitution; Digestive enzymes; Poultry by-product meal; Sobaity sea bream.