Is this a 596c model, 596c HD model or a 596c HD DI model? 
Is the transducer mounted on the transom, inside-the-hull or on the trolling motor? 
Assuming that it is the 596c or 596c HD model: set the Beam Select menu to the 200/83kHz menu setting and the SwitchFire menu to the Max Mode setting.  This will be the best option for showing fish as arches.