The benefits of blend essential oil for GIFT tilapia on the digestion, antioxidant, and muscle quality during cold storage

Abstract Essential oils have been used commercially as feed additives on livestock and poultry due to their broad spectrum antioxidant and disease resistance effects. However, their effects have not been well studied in fish. To this end, this study was conducted in two parts to evaluate the roles of blend essential oil (BEO, cinnamaldehyde, thymol, carvacrol) in fish. First, the growth inhibition effects on two typical pathogens and one beneficial bacterial of tilapia in vitro. Second, a feeding trial of tilapia with or without BEO (300 mg/kg) for 8 weeks (first phase), and further feeding trial of tilapia selected from phase first with or without BEO (300 mg/kg feed), florfenicol (200 mg/kg feed) for 2 weeks (second phase). The results showed that BEO has a broad-spectrum antibacterial effect on tilapia pathogens (Streptococcus agalactiae and Streptococcus iniae) and beneficial bacterial (Bacillus subtilis), but B. subtilis was a bit more sensitive to BEO than florfenicol. BEO added to feed significantly increased the intestine and serum amylase (AMS) activity (P