Parasin I, a peptide fragment derived from the N-terminal region of histone H2A in catfish (P. asotus), plays a critical role in host defense. This antimicrobial peptide is produced through the action of cathepsin D on histone H2A within the skin mucosa of injured P. asotus. Demonstrating efficacy against a spectrum of Gram-positive and Gram-negative bacteria, as well as fungi, Parasin I exhibits minimum inhibitory concentrations (MICs) of 1-2 µg/ml, 1-4 µg/ml, and 1-2 µg/ml, respectively.