The Efficacy of Rosemary Oil and Microencapsulated Essential Oils on <i>Zeuxapta seriolae</i> Mitigation in Yellowtail Kingfish, <i>Seriola lalandi</i>

Two additives, rosemary oil and a commercial herbal product (HP; AROTEC‐G) containing garlic essential oil, carvacrol and thymol were investigated for their potential to reduce the parasitic burden in yellowtail kingfish (YTK; Seriola lalandi ) infected with Zeuxapta seriolae . Naturally infected fish were fed diets supplemented with either 2.5 mL.kg −1 rosemary oil or two concentrations of HP (5 and 10 g.kg −1 ) for 20 days. At 10 and 20 days, the effect of the diets on parasite abundance was evaluated. Feed intake and growth were similar across treatments ( p &gt; 0.05). By day 10, both rosemary oil and HP significantly reduced parasite burden compared to the control ( p = 0.03). Praziquantel (PZQ) baths on days 10 and 20 found that the supplements were more effective in reducing new parasite recruitment rather than eliminating adult parasites. The HP product, at both doses, significantly reduced reinfection by day 20. Rosemary oil reduced parasite load by 43% compared to the control by day 20. Liver and kidney function remained unaffected. This study concluded that rosemary oil and blended essential oils can assist in the management of Z. seriolae infection in YTK culture.