An aquatic subunit vaccine comprises an antigenic fusion protein and suitable carrier or adjuvant. The antigenic fusion protein sequence consists from its amino terminus to carboxyl terminus of a receptor binding motif and a translocation domain of Pseudomonas aeruginosa exotoxin A and has the amino acid sequence of SEQ ID No: 8; a viral antigenic protein affecting fish disease; and a signal peptide having the amino acid sequence of SEQ ID No: 10.