led to a signifi- cantly increased mortality, suggesting an important role of PmproPOs in shrimp’s defense against fungal infection. Using L-DOPA, dopamine or DHI as a substrate, the melanization reaction products exhibited in vitro antimicrobial activities towards Gram-negative bacteria (Vibrio harveyi and Vibrio parahaemolyticus) and Gram-positive bacteria (Bacillus subtilis)