UNDERWATER RADIOTELEMETRY OF ELECTROENCEPHALOGRAPHIC ACTIVITY FROM THE HIME SALMON, LANDLOCKED SOCKEYE-SALMON ONCORHYNCHUS-NERKA

The monitoring of neural signals of aquatic animals under freely behav ing condition is essential to understand their neural mechanism of beh avior. Here the authors introduce an underwater radio-telemetry system to receive electroencephalographic (EEG) signals from the fish freely swimming in freshwater areas. The system uses simple and generally av ailable instrumentation method, and is composed of a transmitter and a receiver. The transmitter attached to the fish uses a 78 similar to 9 8 MHz main carrier frequency which is modulated by a 1.6 kHz pulse-fre quency modulated subcarrier. It is radiated directly from the oscillat ing coil to the water, and travels from the subsurface transmitter to the receiver placed in the air. For receiving and demodulating the tra nsmitted signals, a conventional FM broadcasting receiver is used with a frequency to voltage converter and a low-pass filter. The system tr ansmitted high fidelity signals for several hours within a range of 5 m. By using the system, EEG signals (olfactory bulbar wave) were succe ssfully received for the first time from the fish (landlocked sockeye salmon Oncorhynchus nerka) freely swimming in an outdoor pond.