A newly designed underwater antenna and its application to underwater radio-telemetry for measuring electroencephalographic activity from the rainbow trout freely swimming in natural environments.

A novel underwater antenna (which we named an 'aquaerial') for telemetering the biological signals from freely swimming fish in freshwater natural environments is presented. It is designed for receiving a 90-100 MHz carrier wave and consists of plural unit receiving antennas (UAs). The plural UAs are placed underwater to cover the area where the target fish carrying the transmitter is swimming. The UAs are equally spaced and have a directional coupling amplifier to supply the signals received to the coaxial cable. The optimal length of the UA was found to be 16.5 cm (a half wavelength in water) and optimal spacing was 2 m (one wavelength along coaxial cable) when 95 MHz was used as the carrier frequency. Using this 'aquaerial', long-term monitoring of EEG signals from the olfactory bulb of the rainbow trout (Oncorhynchus mykiss) swimming freely in natural environments was achieved.