Other mistake: Wouldn't the fish have set off the motion detector?
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Suggested correction: Maybe, it depends on the sensor technology. Infrared detectors, no. The fish are about the same temperature as the water. Ultrasonic detectors, no. The sound doesn't penetrate the tank. Radar detectors, no. Radar does not penetrate the water. Laser detectors, no. The beams would reflect primarily off the tank. Image analysis, maybe. The algorithm comparing the image over time might pick up the fish motion, but the discrimination would have been adjusted already to eliminate false alarms.
