This study evaluated the effects of phytase supplementation on growth performance and apparent digestibility of Nile tilapia (Oreochromis niloticus) in a commercial fish farm setting. Nile tilapia (6300 male, 57.48 ± 1.04 g) were randomly stocked into 42 floating cages. The experimental design was completely randomized, comprising six treatments and seven replications. Fish were fed five phosphorus deficient plant-based diets with graded levels of phytase supplementation (0, 500, 1000, 1500, 2000 UF kg⁻¹) and an additional diet containing phosphorus supplementation to meet the requirement of this fish species (positive control). After 97 days of feeding, growth performance data were collected and 900 fish (500 ± 10 g) were relocated to 6 floating cages for the digestibility assessment. Quadratic polynomial regression analysis indicated 1537.5 and 1593.2 UF kg⁻¹ as the optimum dietary levels for daily weight gain and feed conversion rate, respectively. Including 2000 UF kg⁻¹ resulted in the higher dry matter, crude protein, energy, and ash apparent digestibility coefficient values. Therefore, phytase supplementation from 1500 to 2000 UF kg⁻¹ is recommended to enhance growth performance and nutrient bioavailability of Nile tilapia reared according to industry practices.

This study aimed to evaluate the effect of dietary orange peel fragments (OPFs) enriched with vitamins C (C) and E (E), as well as zinc (Zn) on the growth performance, hematological profile, immunological parameters, antioxidant capacity, and fillet lipid peroxidation of Nile tilapia subjected to heat/dissolved oxygen-induced stress (HDOIS), transport-induced stress (TIS), and Aeromonas hydrophila infection (BC). A group of 500 male Nile tilapia (2.7 ± 0.03 g) was randomly distributed in twenty-five 250 L aquaria (20 fish/aquarium) and fed diets containing OPFs (6 g kg⁻¹), OPFs/C (6 g kg⁻¹/1.8 g kg⁻¹), OPFs/E (6 g kg⁻¹/0.4 g kg⁻¹), OPFs/Zn (6 g kg⁻¹/0.21 g kg⁻¹), or OPFs/C/E/Zn (6 g kg⁻¹/1.8 g kg⁻¹/0.4 g kg⁻¹/0.21 g kg⁻¹) for 100 days. The diets were formulated to contain 30% crude protein and 17 MJ kg⁻¹ gross energy. After the feeding period, three groups of fish were independently subjected to a different type of stress: HDOIS (34 °C) for two days; TIS for four hours, or BC for 15 days. The hematological profile, antioxidant capacity, and fillet lipid peroxidation were determined before and after all the stress treatments, along with immunological parameters, which were investigated only for the fish subjected to bacterial infection. In summary, the results showed that growth was not affected by the OPFs, nor by the OPFs enriched with C, E, and Zn; bacterial infection determined anemia for the fish fed any of the experimental diets; the OPFs did not prevent lipid peroxidation under TIS and BC; on the other hand, when enriched with C/E/Zn, lipid peroxidation decreased under HDOIS and TIS. In conclusion, the OPFs enriched with C/E/Zn showed a synergistic effect that promoted an increase in antioxidant enzyme activity, a decrease in lipid peroxidation, and the maintenance of the hematological profile under HDOIS and TIS, but they were not able to maintain the health status under BC.