Dietary supplementation of dry oregano leaves increases the innate immunity and resistance of Nile tilapia against Streptococcus agalactiae infection

Abstract

This study aimed to evaluate the influence of increasing concentrations of dietary dry oregano leaves (DOL), ranging from 0 to 0.15%, on different performance parameters of Nile tilapia.Hence, two separate experimental trials testing growth factors (Trial 1) and innate immunity and disease resistance against Streptococcus agalactiae infection (Trial 2) were conducted with a total of 464 tilapia juveniles and two to four replicates. As a result, dietary inclusion of DOL did not induce significant effects on growth performance, hematological parameters, and fillet composition. However, there were significant differences in lysozyme activity between groups of DOL at 0.075% and the control (0%). Moreover, the bactericidal index of the positive control and groups supplemented with DOL were significantly higher than baseline treatment groups. For disease resistance, there was a reduction of 15% in the relative risk of streptococcosis in fish juveniles after dietary inclusion of oregano at 0.15%. In conclusion, the inclusion of DOL in tilapia diets resulted in no significant gains in terms of growth; nevertheless, the immune system and resistance of tilapia against S. agalactiae infection were significantly improved. † Amanda H. do Espirito Santo and Túlio S. de Brito should be considered joint first authors.

Oregano essential oil ( Origanum vulgare ) dietary supplementation improved growth performance, body protein retention and muscle hyperplasia of the Neotropical catfish Lophiosilurus alexandri

“…The beneficial effects of OEO on fish growth are generally attributed to the antimicrobial property of the phenolic compounds carvacrol and thymol (Alagawany et al, 2021; El‐Hack et al, 2016; Giannenas et al, 2012) and to the modulation of the intestinal microbiota (Giannenas et al, 2012; Ran et al, 2016; Zhang et al, 2020). In addition, OEO can increase the nutrient digestibility (Espirito Santo et al, 2019; Giannenas et al, 2012; Zheng et al, 2009) by the activation of digestive enzymes (Zhang et al, 2020). Carvacrol and thymol can also act to eliminate radicals and improve antioxidant defences (Abdel‐Latif et al, 2020; Mohammadi et al, 2020) and thus reduce damage to oxidative tissues and save nutrients for growth (Diler et al, 2017; Mohammadi et al, 2020; Zheng et al, 2009).…”

“…However, as in this study, diets supplemented with oregano leaves did not promote morphometric changes in the intestine of O . niloticus (Espirito Santo et al, 2019).…”

“…For muscle growth analysis, muscle samples from two fish per tank ( n = 8 per treatment) were collected by removing a fragment from the region of the right dorsal muscle of the fish. For the intestinal histomorphometry, intestine samples from two fish per tank ( n = 8 per treatment) were collected removing approximately 5 cm of the anterior portion of this organ according to Espirito Santo et al (2019). After tissue collections, the carcasses of all fish were pooled ( n = 4 per treatment) to chemical composition analysis.…”