Vessels used for trawler fishing. They drag along a tunnel-shaped net (trawl) whose size and mesh vary according to ship size and fish species. Various types are in use: freshfish trawlers, freezer trawlers, factory trawlers, and super-trawlers. After catching, the fish must be processed and stored as quickly as possible. In case of large factory trawlers, the fish is processed by automatic systems inside the ship, i.e. killing and gutting, heading, washing and scaling, skinning, cutting and filleting, weighing, freezing and packing. Fresh fish is packed together with pieces of ice in deep freeze compartments at –30°C, or fully preserved in tins, whilst by-products such as fish-meal or oil are kept in special compartment and tanks. See also Supertrawler HELEN MARY.