A blend of herbal essential oils enhanced the growth performance, blood bio-immunology traits, and intestinal health of Nile tilapia (Oreochromis niloticus)

Nile tilapia were fed four levels (0, 0.25, 0.5, and 1 ml/kg) of a liquid blend of herbal essential oils (EOs) containing carvacrol, oregano, 1,8 cineol, thymol, pinene, pinene β, limonene, and propylene glycol for 60 days. The results showed higher final weight, weight gain, and specific growth rate (P<0.05) in fish delivered 0.25 and 0.5 ml EOs/kg than the control. However, the feed conversion ratio was markedly reduced in fish fed 0.5 and 1 ml EOs/kg (P<0.05). Lipase showed enhanced activity in fish subjected to a blend of EOs, while fish fed 0.5 ml/kg of EOs blend had higher amylase activity (P<0.05) than the other levels. Lysozyme activity and superoxide dismutase showed a higher value in fish that received 0.5 ml EOs/kg. Additionally, phagocytic and catalase activities were enhanced in fish that received 0.5 and 1 ml/kg while phagocytic index was enhanced in fish fed 1 ml/kg (P<0.05). Interestingly, the total immunoglobulin level was markedly higher, while malondialdehyde was lower in EOs-subjected fish (P<0.05) than in control. The histomorphology appearance of the intestine, liver, and spleen was enriched in EOs-treated fish compared to the control fish. In conclusion, the growth performance, feed efficiency, and blood bio-immunological indices were best in fish fed 0.5–1 ml of EOs blend per kg.