Improved Protection of Rainbow Trout Against Furunculosis by an Autologous Vaccine Under Experimental Conditions

Despite vaccination with oil-adjuvanted vaccines against vibriosis and furunculosis, sea reared rainbow trout in Denmark often encounter outbreaks of furunculosis during warm summer periods. To address this issue under experimental conditions, two groups of rainbow trout were vaccinated by i.p. injection with two different oil-adjuvanted vaccines: (1) a commercial vaccine comprising Vibrio anguillarum serotype O1 and O2, and Aeromonas salmonicida subspecies salmonicida bacterins, with all bacteria originating from Atlantic salmon, and (2) an experimental vaccine based on cultures of the same bacterial species originating from rainbow trout reared in Danish sea farms. The experiment also included a third group of non-vaccinated controls. All fish were individually chip-tagged to allow mixing of all groups in three replicate aquaria. After 770 dg (day degrees) or 77 days at 10⁰C, half of the fish in each group were challenged by i.p. injection of 1x105 cells of the A. salmonicida isolate used in the experimental vaccine. The other half was tagged by cutting off the adipose fin (non-injected cohabitants). While the non-vaccinated, i.p.-injected fish all died within 2 weeks, a certain level of protection was evident among the vaccinated groups although high mortality also occurred here. No mortality/clinical disease was evident among the non-injected cohabitants. However, when the water temperature was gradually risen to 15-17-20⁰C, the cohabitants started to die. Some variability was evident between replicate tanks, but the experimental vaccine tended to provide better protection than the commercial counterpart. The results indicate that tailor-making of a vaccine against furunculosis for sea reared rainbow trout in DK is an important approach for optimal protection.