Studies Of Immunoglobulin Structure And Diversity In Non-Salmonid Marine Fish     Andrew Dacanay1, E. B. Bentley1, 2, L. L. Brown1, S. C. Johnson1   1National Research Council Canada Institute for Marine Biosciences, Halifax, Nova Scotia; 2 Department of Biology, Dalhousie University, Halifax, Nova Scotia       Our laboratory is investigating the immune responses of cold-water marine finfish to vaccination and disease exposure.  We have investigated the vaccination of haddock  (Melanogrammus aeglefinus L) in terms of the antibody response, immunoglobulin (Ig) quaternary structure and Ig diversity. Specific antibody levels and immunoglobulin diversity was determined for groups of haddock that were immunized at 12oC with either a commercial vaccine against Vibrio anguillarum and Aeromonas salmonicida, TNP-KLH conjugate and adjuvant, or saline and adjuvant. A non-injected group served as a control.  We were unable to detect antibody responses to any of the antigens by ELISA. Two-dimensional gel electrophoresis was used to investigate immunoglobulin diversity.  No detectable differences were observed in the isoelectrophoretograms between groups. We found that the overall structure of haddock Ig is similar to that of salmonids and is comprised of 85 kDa heavy chains and 25 kDa light chains. Data from non-reducing, denaturing agarose/acrylamide gel electrophoresis and analytical FPLC suggest that haddock Ig has a similar quaternary structure to salmon Ig.  However, with respect to levels of disulphide cross-linking, haddock Ig appears to exist in its highest cross-linked form as a trimer.  We have recently expanded upon this study to investigate the physical structure of plasma immunoglobulin from seven orders and 13 species of marine and anadromous fish.  In their highest cross-linked forms elasmobranch Ig is a pentamer and, with exception of the Gadiformes species and the rainbow smelt, teleost Ig is a tetramer. All species examined within the Gadiformes (Atlantic cod, haddock, pollock, and tusk) have immunoglobulin composed of trimers and lower forms. From these results it is evident that phylogenetic position influences the extent of Ig disulphide cross-linking.