Promotion of growth and resistance against Aeromonas hydrophila in Nile tilapia juveniles supplemented with Citrus limon extract

Abstract

This study aimed to investigate the effects of dietary supplementation with Citrus limon (L.) extract (CLE) on the growth, hematological, and biochemical parameters of Nile tilapia juveniles (Oreochromis niloticus L.). The chemical composition of CLE was detected using nuclear magnetic resonance and mass spectrometry. Three hundred and sixty fish (12.80 ± 0.13 g) were distributed in a completely randomized experimental design with six treatments and four replicates (15 fish per tank). Six diets with different levels of CLE in the diet – 0.0 (control), 0.2, 0.4, 0.8, 1.6, and 3.2 g kg−1 – were evaluated for 60 days, followed by 8 days of Aeromonas hydrophila challenge. The bacterial inoculum was diluted in sterile saline at 1 × 107 colony-forming units mL−1. The major constituents of CLE were phenolic compounds (mainly flavonoids) and polysaccharides. Quadratic regression showed that fish supplemented with 1.6 g CLE kg diet−1 improved final weight, weight gain, feed intake, feed conversion ratio, and perivisceral fat index. Before bacterial infection, fish supplemented with 1.6 g CLE kg diet−1 showed a higher hepatosomatic index and erythrocytes (according to linear regression) and higher plasma total protein and hemoglobin (according to quadratic regression). After bacterial infection, quadratic regression showed that 0.8–3.2 g CLE kg diet−1 reduced the plasma aspartate aminotransferase levels and mortality of juveniles. In conclusion, adding 1.6 g CLE kg diet−1 is recommended to improve Nile tilapia juveniles' growth performance, health, and survival after A. hydrophila infection.