Use of adjuvanted vaccines to lengthen the protection against lactococcosis in rainbow trout (Oncorhynchus mykiss ) Carmen Ravelo a , Beatriz Magarin ˜os a , M. Carmen Herrero b , Llorenc ¸ Costa b , Alicia E. Toranzo a , Jesu ´ s L. Romalde a, * a Departamento de Microbiologı ´a y Parasitologı ´a. Facultad de Biologı ´a, Universidad de Santiago de Compostela, 15782, Santiago de Compostela, Spain b Laboratorios HIPRA S.A. 17170 Amer, Girona. Spain Received 31 October 2004; received in revised form 18 May 2005; accepted 19 May 2005 Abstract In this work, we evaluated the effect of the inclusion of different adjuvants in the vaccine formulation against Lactococcus garvieae in comparison with an aqueous bacterin. The aqueous and non mineral oil adjuvanted vaccines (Montanide-ISA-763- A and Aquamun) yielded a good protection 4 weeks after the immunization (RPS of 82.6, 84.8 and 86.9, respectively). The protective rates obtained for the adjuvants Montanide-IMS-2212 (water based nanoparticles with immunostimulant) and Carbomer (high molecular weight polymer organic of polyacrylic acid) were 45.7% and 56.5%, respectively. We also evaluated the duration of protection confered by Aquamun adjuvanted-vaccine in comparison with the aqueous bacterin. Three months after vaccination, the RPS values obtained with the aqueous vaccine was 40% whereas with the Aquamun adjuvanted-vaccine the protection increased to values of 92%. In addition, a long lasting protection was observed with this adjuvanted vaccine with RPS values of 90% and 83.3% in the challenges performed at 6 and 8 months post-vaccination, respectively. D 2005 Elsevier B.V. All rights reserved. Keywords: Lactococcus garvieae ; Rainbow trout; Vaccination; Adjuvanted vaccines 1. Introduction Lactococcosis or streptococcosis, caused by Lacto- coccus garvieae , is one of the most important fish diseases in intensive aquaculture, causing substantial economic losses specially in the culture of yellowtail (Seriola quinqueradiata ) in Japan and rainbow trout (Oncorhynchus mykiss ) in Europe and Australia (Kusuda et al., 1991; Bercovier et al., 1997; Eldar and Ghittino, 1999; Eldar et al., 1996; Dome ´nech et al., 1993; Ravelo et al., 2001a). The existence of two serological groups associated with the presence of capsular material has been demonstrated for L. gar- 0044-8486/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2005.05.027 * Corresponding author. Tel.: +34 981 563100x13253; fax: +34 981 596904. E-mail address: mpromald@usc.es (J.L. Romalde). Aquaculture 251 (2006) 153 – 158 www.elsevier.com/locate/aqua-online