Background <p><i>Aeromonas hydrophila</i> is a major freshwater fish pathogen responsible for significant economic losses to the aquaculture industry. Its virulence factors include proteins involved in primary adhesion, pili, flagella, O-antigen, outer membrane proteins, and adhesins, etc. Among these, the outer membrane maltose-inducible porin functions as an adhesin and can be a potential vaccine candidate.</p> Methods and results <p>In the present study, the maltose-inducible porin (LamB) of <i>A. hydrophila</i> was heterologously overexpressed, purified and assessed for its immunogenic potential in a murine model. The gene encoding mature LamB was cloned into pRSET-A expression vector. Recombinant LamB (rLamB) carrying a 6×-histidine tag was expressed as inclusion bodies in <i>E. coli</i> BL21(λDE3), purified from solubilized inclusion bodies by metal affinity chromatography to near homogeneity, and refolded. Immunization of mice with rLamB generated high-titer anti-rLamB antibodies with high specificity. The anti-rLamB antisera agglutinated live <i>A. hydrophila</i> cells in vitro and recognized other <i>Aeromonas</i> species, suggesting its possible application in the diagnosis of <i>Aeromonas</i> infection and potential as a candidate for broad-spectrum vaccine development. Antibody isotyping and cytokine ELISA indicated a T_H2-biased mixed immune response.</p> Conclusion <p>Recombinant LamB of <i>Aeromonas hydrophila</i> elicited strong and specific immune responses, generating high-titer antibodies that agglutinated live bacteria and cross-reacted with other <i>Aeromonas</i> species. These findings collectively suggest that rLamB of <i>A. hydrophila</i> may have potential as a vaccine candidate for broad-spectrum vaccine development and possible diagnostic applications against heterogeneous <i>A. hydrophila</i>.</p>