Cobb County Government
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Fish Monitoring

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Fish are collected following protocols outlined in the document Standard Operating Procedures for Conducting Biomonitoring on Fish Communities in Wadeable Streams in Georgia. The stream reach to be sampled is 35 times the mean width of the stream. This sample length usually encompasses three riffle-run-pool sequences and will adequately represent species richness, abundance, and community structure of the fish population.


Georgia’s fish biomonitoring season usually occurs from early April until mid October, but the duration is variable due to water levels and temperature. Sampling is optimal during the summer months when water levels are low and fish populations are stable and sedentary. When sampling, one individual operates a backpack electrofishing unit; other members of the sampling team carry nets and a bucket to transport the fish. The sampling team moves upstream, so as not to disturb the areas yet to be sampled. The anode ring of the electrofishing unit sends out a charge which momentarily stuns the fish and draws them out of their habitat. The fish are then scooped up with a net and collected for identification. Riffles are sampled by setting up a seine net at the bottom and having the electrofishing unit move downstream toward the seine. Stunned fish will be carried by the current into the net; the sampler may need to shuffle and kick his feet to dislodge any fish that may be laying on the substrate (stream bottom). The net is then raised and captured fish are placed in a bucket. Fish are identified to the species level, counted, examined for anomalies (such as lesions and tumors), and released. Results from field sheets are transferred to a computer database so that the fish populations may be analyzed. A useful analytical tool is the Index of Biotic Integrity, which integrates characteristics of the fish community, population and individual organisms to assess biological integrity.