Several studies prove the effect of polyvalent vaccine on increasing lysozyme activity, for example, the combination of V. anguillarum and Edwardsiella piscicida vaccine in turbot [38], the polyvalent yersiniosis and streptococcosis/lactococcosis vaccine in O. mykiss [6] and the bivalent A. salmonicida and E. tarda vaccine in turbot [39]. The gene discussed is LYZ; the disease is Yersinia infectious disease.