Inhibitory Effects of Rosemary Oil on the In Vitro Growth of Six Common Finfish Pathogens

摘要

Additives are commonly used in feed to enhance fish performance, health, and well-being. In recent years, antibiotics have received increased scrutiny owing to concerns about overuse and their environmental impact. These concerns have generated a desire for naturally derived alternatives for the aquafeed industry. For screening purposes, we examined the in vitro effects of an essential oil on bacteria commonly associated with fish diseases. Six concentrations of rosemary Rosmarinus officinalis oil (0.1, 0.3, 0.5, 0.7, and 0.9 mu L/mu L of 1% Tween-20 and pure rosemary oil [1.0]) were used against Flavobacterium psychrophilum, Yersinia ruckeri, Aeromonas salmonicida, and three warmwater bacterial pathogens, A. hydrophila, Edwardsiella ictaluri, and E. tarda, along with a control treatment (1% Tween-20 only). After incubation, the mean zone of inhibition around the disks was measured. While most concentrations were found to inhibit pathogen growth, a concentration of 50% or more was found to have significantly higher effects on most of the pathogens tested. Rosemary oil was found to inhibit the growth of F. psychrophilum to the greatest extent and had a limited effect on the other fish pathogens. Although rosemary oil was shown to inhibit the growth of some bacterial fish pathogens in experimental trials, further laboratory and field studies are required to determine whether rosemary oil as a feed additive has any application as part of an integrated fish health management strategy.