Responses to graded levels of zinc amino acid complex in Nile tilapia (Oreochromis niloticus)

Zinc (Zn) is an essential micronutrient that plays a crucial role in fish development and physiology. This study aimed to evaluate the effects on growth and health in Nile tilapia (Oreochromis niloticus) supplemented with graded levels of zinc amino acid complex (Zn-AA) and subjected to transport stress. Nile tilapia (21.78 +/- 0.17 g; (n = 12 fish per tank; stocking density of 1.045 kg(- 3)) were fed with 0, 25, 50, 75, or 100 mg Zn-AA kg(- 1) (equivalent to 77.49, 102.69, 127.89, 153.09, or 178.29 mg Zn kg(- 1)) in extruded diets (280 g kg(- 1) digestible protein; isoproteic and isocaloric) for 60 days. At the end of the experimental period, after growth performance measurements, the fish were transported by car for 3 h, and blood collection was performed. The linear regression showed that the best growth performance (final weight, final biomass, weight gain, specific growth rate, and feed intake) was found in fish fed with 100 mg Zn-AA kg diet(- 1) (p < 0.05). The increased dietary Zn-AA increased linearly plasma triglyceride levels, hemoglobin, mean corpuscular hemoglobin, and leukocyte values and reduced plasma total protein, cholesterol (total and LDL), and aspartate aminotransferase levels (p < 0.05). According to quadratic regression, the highest plasma glucose and alanine aminotransferase values were found in the control group (p < 0.05). In conclusion, under the conditions of this study, 100 mg Zn-AA kg diet(- 1) is recommended for Nile tilapia as it can improve their growth, metabolism, physiology, and immunity.