The present invention relates to antimicrobial peptides, isolated and purified from extracts of tilapia (Oreochromis niloticus) gills. Such peptides may be produced by chemical synthesis or by expression in heterologous systems, such as bacteria and yeasts, by conventional molecular biology techniques. These peptides show antimicrobial activity against various organisms, including Gram positive bacteria, Gram negative bacteria, fungi and viruses. The invention also includes compositions to for controlling pathogens comprising these antimicrobial peptides. The use of such peptides in vaccine preparations, as molecular adjuvants, is also part of the invention.