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allowed access to smaller fish. We constructed each cage of four panels that were <br />1.2 m high and two meters wide. The panels were framed with wood and covered with <br />1.6 mm fiberglass screen. The four panels were bolted together and the cage was <br />placed in the backwater and secured with fence posts placed at each comer. The <br />position of the treatments within each backwater was randomized. <br />The third treatment allowed us to: (1) determine the combined effect of the smaller <br />fish (i.e. red shiner, young Colorado squawfish, etc.) on the backwater invertebrate <br />community, and (2) to check for cage effect (whether any statistical significant <br />differences between the control treatment and the closed treatment were due to the <br />presence or absence of fish, or to some physical differences created by the cage). <br />Sampling <br />Enclosures were installed August 6-8, 1992. Samples were taken August 14-15 <br />(week 1), August 21-22 (week 2), August 28-29 (week 3), September 11-12 (week 5), <br />September 25-26 (week 7), and October 16-17 (week 10). During each sampling <br />period 30 benthic cores (19 mm in diameter) and five vertical plankton tows (20 cm in <br />diameter) were taken from each treatment within each backwater. Samples were <br />preserved in a 5% formalin solution. Fluorescence of L vivo chlorophyll a was also <br />measured in each treatment. <br />In the laboratory the samples were washed through a 63 pm mesh screen to <br />eliminate fine silts and clays. Nematoda, Oligochaeta, Gastrotricha, Chironomidae, <br />Ceratopogonidae, Corixidae, Cladocera, Copepoda (adults, copepodites, and nauplii), <br />5