Fish & Shellfish Immunology (1997) 7, 429–437 Effects of -glucans on the non-specific immune responses of turbot (Scophthalmus maximus L.) M. SANTARÉM, B. NOVOA AND A. FIGUERAS* Instituto de Investigaciones Marinas, CSIC, Eduardo Cabello 6, 36208 V igo, Spain (Received 12 December 1996, accepted in revised form 17 April 1997 ) Several non-specific immune responses of turbot (Scophthalmus maximus L.) were enhanced after the administration of -glucans and/or O-antigen of Vibrio damsela. Bactericidal activity of turbot leucocytes varied depending on the bacterial virulence. Whilst no di#erences in bactericidal activity were observed among treated and untreated fish when a virulent strain of V. damsela was used, leucocytes from glucan plus O-antigen-treated turbot e$ciently destroyed an avirulent V . damsela strain. Respiratory burst activity was also increased seven days post-injection in leucocytes from glucan plus O-antigen-treated fish. Lysozyme activity was significantly higher in serum from fish injected with any combination of immunomodulators (glucan, O-antigen, glucan plus O-antigen) compared with controls.  1997 Academic Press Limited Key words: turbot, Vibrio damsela, immunostimulants, glucan. I. Introduction The use of immunostimulants is being introduced into fish farming routine procedures as a prophylactic measure. Since, so far, they have not shown any of the negative side-e#ects that antibiotics and live vaccines may have on the consumer and on the environment, they are presented as an attractive alternative way of controlling bacterial infections (Anderson, 1992; Secombes, 1994). The e#ects of di#erent immunostimulants on the immune response of a variety of fish species have been examined (Siwicki, 1987, 1989; Kajita et al., 1990; Robertsen et al., 1990; Siwicki et al., 1990; Nikl et al., 1991; Yano et al., 1991; Chen & Ainsworth, 1992; Matsuyama et al., 1992; Raa et al., 1992; Engstad & Robertsen, 1993; Jørgensen et al., 1993 a,b; Robertsen et al., 1994) showing that the non-specific response was enhanced. Another advantage of immunostimulants is their use as adjuvants for fish vaccination (Anderson & Jeney, 1992; Jeney & Anderson, 1993; Rørstad et al., 1993). In previous papers we have described the specific and non-specific immune response of turbot (Scophthalmus maximus), an important fish species in Spanish aquaculture (Santarém & Figueras, 1994, 1995). In the present paper the e#ect of glucan on the non-specific turbot immune responses against Vibrio damsela is evaluated. 429 1050–4648/97/060429+ 09 $25.00/0/fi970096  1997 Academic Press Limited