Several studies have shown that yeast glucans are activators of the non specific defense mechanisms in vertebrates including fish. For example, glucans injected (ip) into fish enhance immunity to gram-negative pathogens, such as Aeromonas salmanicida (Nikl et al., 1993, Aakre et al., 1994), and increase the activity of serum lysozyme and complement (Yang et al., 1991, Jorgensen, et al., 1993). Recently salmonid responses to VYS-2, a vaccine produced for protection of fish to motile aeromonads in Russia, indicated that non-specific immune responses were also stimulated by this vaccine. Elucidation of the non-specific immune response of fish to disease and the effects of glucans and other immune stimulators like, VYS-2 on these responses will determine the applicability of glucan and other non-specific immune stimulator in commercial fish industries.

Our first objective was to determine the effect of these immuno-stimulators on various immune parameters in rainbow trout. During the first phase of the project, optimum conditions for assaying lysozyme, alternative complete pathway and phagocytosis was defined for rainbow trout. These parameters were tested as well as hematocrit, white blood cell counts, and agglutination and precipitation titers to selected antigens, and histopathology of the skin. Second, the ability of glucan and VYS-2 to enhance protection of rainbow trout to challenge with Vibrio anguillarum was determined.

Literature cited

1.  Aakre, R., Wergeland, H.I., Aasjord, P.M. and Endresen, C. 1994. Enhanced antibody response in Atlantic salmon (Salmo salar L.) to Aeromonas saimonicida cell wall antigens using a bacterin containing B-1,3-M-glucan as adjuvant. Fish and Shellfish Immunology 4: 47-61.

2.  Jorgensen, J.B., Sharp, G.J.E., Secombes, C.J., and Robertsen, B. 1993. Effect of yeast -cell-wall glucan on the bactericidal activity of rainbow trout macrophages. Fish and Shellfish Immunology 3: 267-277.

3.  Nikl, L., Albright, L.J., and Evelyn, T.P.T. 1991. Influence of seven immuno-stimulators on the immune response of coho salmon to Aeromonas saimonicida. Diseases of Aquatic Organisms 12: 7-12.

4.  Yano, T., Matsuyama, H. and Mangindasn, R.E.P. 1991. Polysaccharide-induced protection of carp, Cyprinus carpio L., against bacterial infection. Journal of Fish Diseases 14: 577-582.