Natural products as functional food ingredients for Nile tilapia challenged with Aeromonas hydrophila

Functional foods employ ingredients whose purpose is not necessarily to supply a possible nutritional deficiency, but rather to offer benefits to human and animal health. In this context, the present study aimed to investigate the use of oregano essential oil (OEO) and ethanolic extract of propolis (EEP) as functional foods for Nile tilapia challenged with Aeromonas hydrophila. Healthy fingerlings (7.67 +/- 0.86 g of mean initial weight) distributed in 60-L aquariums were used in the experiment, maintaining good water quality. The treatments consisted of 2.22 g of EEP kg feed(-1) (treatment 2), 0.5% OEO feed(-1) (treatment 3), and one control feed (treatment 1), with seven replications. After 30 days of feeding, the animals were subjected to sanitary challenges and observed for 15 days. Zootechnical, survival, and immunological parameters were analyzed, and the variability of intestinal microorganisms was evaluated through denaturing gradient gel electrophoresis (DGGE). The results of this study showed that tilapia fed with feed containing OEO or EEP significantly improved growth parameters compared with the control group, obtaining respective mean values for the control treatment, EEP and OEO: final weight (20.38 +/- 1.6b; 23.15 +/- 2.07a; 24.31 +/- 1.43a), weight gain (12.66 +/- 1.67b; 15.5 +/- 2.04a; 16.65 +/- 1.45a), and body condition (1.66 +/- 0.06b; 1.8 +/- 0.12a; 1.82 +/- 0.11 The). In addition, the addition of OEO effectively improved carcass traits as well as apparent feed conversion (1.91 +/- 0.19b; 1.69 +/- 0.22ab; 1.45 +/- 0.22a) and feed efficiency (0.56 +/- 0.05b; 0.63 +/- 0.07ab; 0.73 +/- 0.13a) compared with the control group (P < 0.05). The two natural additives showed no significant effect on fish immunity, survival parameters after challenge, and hepatosomatic index. However, they presented an effect as growth promoters and on the intestinal microbiome; in the latter, there was an increase in diversity when compared with the control group. It may be concluded that OEO and EEP natural additives can act as growth promoters.