This study describes a method for monitoring the activity of aquatic organisms and reports preliminary results using hydrazine as the pollutant. Activity was detected using strain gages attached to immersed stainless steel paddles. Fish changing position or maintaining their position in the water column created water disturbances, and the relative amount of the water disturbance was used as an index of activity. Analog outputs from the gages were conditioned, amplified, recorded on frequency modulation (FM) magnetic tape, and processed off-line by computer. A computer program was developed that calculated mean absolute voltage levels of combined signals over 1-min intervals.

Preliminary information was obtained in four trials. Fish activity was monitored from 7 a.m. to 2 p.m. with three or four fish per trial. The activity of the control fish and that of the fish exposed to sublethal concentrations of hydrazine were compared by visual inspection of plots of mean 5-min voltage levels. The activity of the exposed fish was inconsistent between trials, variable, and usually not readily distinguishable from the corresponding control fish activity. Nevertheless, this strain gage-paddle apparatus detects fish activity and offers a new technique that has potential as a biological monitor of water and effluent quality.