We numerically studied the enhancement of optical transmission through the periodic arrays of fish-shaped nano structure metallic arrays by using the three-dimensional finite-difference time-domain (3D-FDTD) method, and investigate the influence of lattice constant and hole shape on the optical filtering properties，which is based on transmission. Results show that fish-shaped metallic nano structure has the properties of high transmission efficiency and high filtering quality factor. It is revealed by analyzing the maps of electric-field distribution that optical transmission originates from two different physical mechanisms: localized waveguide resonance mode and surface plasmon resonance mode. Two resonance modes arise in different places in fish-shaped hole region at different time with different forms.