Electrofishing is a survey tool used to estimate species composition, fish abundance, and fish density in freshwater systems using an electrical current.  An electroshocker creates a flow of current between an anode (i.e., ring on a backpack models) and cathode (i.e., rat tail on backpack models) that stuns fish that cross the electric field.  Stunning the fish makes them easier to capture and assess for research and monitoring purposes. 

Electrofishing is a survey technique that stuns fish in freshwater


 Backpack electroshockers are generally used for smaller, wadeable waterbodies; boat or raft mounted electroshockers are generally used for larger waterbodies.  While electrofishing can be a very effective technique for freshwater, electricity has poor conductivity in salt water. (fishionary.fisheries.org/electrofishing)

For an example of boat electrofishing, check out this depletion electrofishing post on the Fisheries Blog!