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Trout normally possess a positive rheotactic behavior, and this behavior is often lost in response to toxic conditions. A continuous automated monitoring system was developed incorporating photoelectric cells and mild electric shock. When a trout no longer displayed positive rheotaxis and moved downstream in the test tank, a series of photoelectric cells were interrupted. This, in turn, caused a mild electric shock to be applied to the downstream portion of the test tank. This electric irritation continued until the fish moved back upstream away from the photocells. A second series of photoelectric cells indicate when the fish remain in the downstream area regardless of the applied electrical impulses. An alarm switch will operate when at least two of the three fish in the same 15-min period pass the photoelectric cells more often than normal or when two fish remain in the extreme downstream portion of the monitoring tank for longer than 5 min. Practical experiences on Rhine water and experiments with toxic substances suggest that this flow-through system is suited for practical application.
water quality, aquatic biology, water pollution, environmental tests, toxicity
Testing and Research Institute of the Netherlands Waterundertakings, KIWA Limited, Rijswijk,