This paper describes the construction and experimetal results of prototype digital telesounder developed to monitor remotely the fish school entered in setnet. The telesounder consists of the sea station and land station. The former consists of an ultrasonic transceiving part of 50 KHz, a hand made 16 bits single board computer (SBC), and a RF MODEM of 9600 bps for data link. The SBC controls the trigger signal to transmit the ultrasonic pulse, maximum detection range, sampling rate in analog to digital converter and data link. The sampling rate of echo data was 80 ${mu}$s. The later consists of a RF MODEM same as the former one and 486 notebook computer which displays the echogram and saves its raw data. The authors carried out some experiments to confirm the practical use of the telesounder. At results the echogram obtained on the land station is sufficiently good and clear to monitor the behavior of fish school in setnet.