Zinc-L-Selenomethionine Improves Growth and Hemato-Biochemical Parameters at Low but not at High Stocking Density for Nile Tilapia Males.

The study aimed to examine the interaction between diets supplemented with zinc-L-selenomethionine (ZnSeMet) and two stocking densities (SD) on Nile tilapia (Oreochromis niloticus) males. Four extruded diets were formulated: 0.0, 0.5, 1.0, and 2.0 mg ZnSeMet kg. Fish (58.00 g) were reared at a low SD (LSD) (15 fish tank or 4,35 kg m) and a high SD (HSD) (45 fish tank or 13,05 kg m). They were randomly distributed in eight treatments in triplicate in a recirculatory aquaculture system (200 L) and were fed until apparent satiation thrice daily for 65 days. The interaction between LSD and 1.0 or 2.0 mg ZnSeMet kg was better than other treatments for final weight (116.50-174.83 vs. 97.33-139.17 g), weight gain (108.83.50-116.83 vs. 39.00-80.83 g), relative weight gain (188.03-201.18 vs. 66.25-139.40%), total final length (20.12-20.63 vs. 17.33-19.00 cm), specific growth rate (1.76-1.83 vs. 0.85-1.45% day) (p < 0.05). In general, the interaction between LSD and 1.0 mg ZnSeMet kg compared to several treatments, showed an increase in plasma total protein (3.23 vs. 2.67-2.78 g dL) and total cholesterol (93.67 vs. 68.50-76.67 mg dL) levels and a reduction in aspartate aminotransferase activity (14.83 vs. 145.67-155.17 U L) (p < 0.05). The highest values for albumin (0.83 vs. 0.57 g dL), glucose (56.00 vs. 45.09 mg dL), and triglycerides (122.33 vs. 68.87 mg dL) in the plasma, erythrocytes (2.22 vs. 2.13 × 10 µL), hemoglobin (9.82 vs. 9.26 g dL), and hematocrit (33.09 vs. 30.21%) were observed in LSD than HSD-reared fish (p < 0.05). In conclusion, adding 1.0 mg ZnSeMet kg at LSD improved fish growth and hemato-biochemical parameters, but it was not effective at HSD.