A fish cage formed from a molecularly oriented single strand filament that is crossed and welded at the intersections to make a net or screen configuration. The filament being molecularly oriented by stretching ratio of about 3:1 and has a cross section of the filament being at least 2 mm2. The filament is an extruded thermoplastic material made from nylon, polyester, polyethylene, polyurethane or polypropylene having a preferred cross section in a D or oval shape to better facilitate welding the intersections. An antimicrobial or biocide may be added to the filament. The screen or net is preferably of a bright color such as yellow, green, white or a translucent white. The screen can also be formed by connecting small injection molded segments together thereby producing a larger screen.
