Fish research. Biologists using electric fishing equipment to stun a fish in a river during a study into their populations. The biologist in the cap at upper left is holding an electrode which provides a burst of electric current which knocks out but does not harm fish in the proximity. The stunned eel seen here is being scooped up in a net, and will be taken to the shore to be classified, weighed and measured. Research such as this helps to ascertain the health of a river and check that fish populations are stable. The fish are released after the measurements have been taken. Photographed in France.