River water is filtered to remove large particles, and then pumped through an 8-chamber exposure system. Each flow-through chamber houses a single fish. An upper and a lower electrode are above and below the fish. The electrodes do not emit any electricity but do pick up weak electrical impulses generated by the fish respiratory movements. The black wires from the upper electrodes are seen on the top of the chamber.
Signals from the 8 fish are transmitted via the electrode wires to an amplifier system. The amplifier enhances the signals approximately 10,000 times before they are relayed to a computer.

The computer stores thousands of data points from each fish over the exposure period. Specially developed software detects four types of responses:

- Ventilatory rate (number of breaths per minute)
- Ventilatory depth (the force of the respiratory muscles, respiratory tracing height)
- Cough rate (number of coughs per minute)
- Total movement (amount of fish movement within the chamber).

This electrical tracing shows a series of (10) ventilatory breaths. If that tracing were from 20 seconds of data, the ventilatory rate (i.e. frequency of peaks per 20 second interval) would be 30. Note that the height (ventilatory depth) of the peaks is relatively constant.
In the middle tracing, the peak height is notably greater. This set of peaks shows a cough response. There are actually two types of cough responses. The first (leftmost) peak is a "spike cough," followed by s several normal ventilatory breaths. The last peak in this trace shows a "high frequency cough." A high frequency cough is a rapid reversal of water through the fish gills.
The bottom tracing shows momentary whole body movement of a fish inside a chamber. The electrodes are picking up muscle movement much greater than would be generated from respiratory muscles alone.
If ventilatory signals from at least 6 out of 8 fish fall outside a normal range, than an "alarm" signal is generated. This signal can trigger an automated phone call to managers, indicating some suboptimal water quality. The alarm also triggers an automated water sampling device to make collections for later analysis. A series of in-line electrodes (not shown) measures dissolved oxygen, temperature, pH and salinity). This additional water quality monitoring helps define why the fish fall outside the range of normal ventilatory activity.