a system for counting fish in a body of water uses one or more acoustic focusing liquid lens transducers each of which includes a large number of individual piezoelectric elements arranged in an arc to create a fan - shaped pattern of adjacent beams , each of which has a narrow beam width . an electrical counting circuit includes a clock producing a series of timing pulses supplied to a plurality of binary coded decimal actuated switch circuits , one of which initiates sequential operation of transmit pulses from individual transducer elements . timing of receiver operation is also controlled by said timing pulses after a delay to minimize &# 34 ; ringing &# 34 ; of the transducer elements from the transmit pulses . received echo signals are amplified , threshold detected and converted to uniform pulses . a second bcd actuated switch circuit cooperates with a series of range gates also connected to receive said timing pulses to control the distribution of the uniform echo pulses to one of a series of counters each of which receives and counts pulses from a single transducer element . display means connected to the counters make it possible to read out counts on individual sectors individually or collectively or to print out counts from the counters at specified time intervals . where a plurality of liquid lens transducers are used , they are connected to the same clock pulses such that they operate in synchronism .