fishfinder

thumb|250px|right|Fathometer sonar|alt=Cabin display of a commercial or oceanographic [[fathometer sonar]]

A fishfinder or sounder (Australia) is a sonar instrument used on boats to identify aquatic animals, underwater topography and other objects by detecting reflected pulses of sound energy, usually during fishing activities. A modern fishfinder displays measurements of reflected sound on a graphical display, allowing an operator to interpret information to locate schools of fish, underwater debris and snags, and the bottom of a body of water. Fishfinder instruments are used both by recreational and commercial fishermen, as well as by marine biologists. Modern electronics allow a high degree of integration between the fishfinder system, marine radar, compass and GPS navigation systems.