Serum immunoglobulins (Igs) from Israeli carp were purified using affinity chromatography. Fish were immunized with purified mouse IgG, and the specific fish antibodies were purified from the immune serum on a mouse IgG-immobilized agarose gel. Rabbit anti-Israeli carp Igs (R
I. carp Igs) antibodies were produced following hyperimmunization with mouse IgG specific carp antibodies. SDS-PAGE analysis under reducing condition showed that Israeli carp Igs were composed of two
-like heavy chains with about 82 and 50 kd, respectively, and one light chain with about 25 kd. On immunoblotting analysis, however, R
I. carp Igs failed to react with the light chain. When both protein A and protein G-purified normal carp Ig were compared with mouse IgG-specific Israeli carp Ig, no significant structural differences among them were observed. To investigate if there is any homology between other fish Ig molecules, cross-reactivity of R
I. carp Igs against Ig molecules from 6 different fish sera and mouse control serum was checked on immunoblotting analysis. As a result, R
I. carp Igs responded to Israeli carp, common carp, and tilapia Ig molecules. In flow cytometry study, however, R
I. carp Igs appeared to recognize 42.0%, 35.8% and <5% of Israeli carp, common carp and tilapia
head kidney cells, respectively. The result suggests the heterogeneity between receptor Igs on B-like lymphocytes and soluble Igs in serum. It is crucial to obtain pure fish Igs to produce reagent antibodies as tools for the study on their specific immune responses.