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Direct effects The taxa which showed the greatest direct effects of the treatments were the chironomid genus Tanypus, the corixidae, and the planktonic adult copepods (including the predominant species Eucyclops s eratus . Corixidae and TanXpus are predators T n us may be omnivorous; see Merritt and Cummins 1984). The copepod genus, Eucyclops, is predominantly herbivorous (Wetzel 1983). All three groups were generally lower in the control areas (no exclusion) and higher in the perforated and closed areas where fish predation would be expected to be either diminished or absent. By week five adult copepod numbers declined. The decline was less pronounced in the controls than in the other treatments (Table 4). Midges of the subfamily Tanypodinae tend to be low in respiratory pigments and therefor are concentrated in the surface flocculants, while the Chironominae have abundant pigments and are capable of burrowing deeper into anoxic sediments (Shiozawa and Barnes 1977). The difference in burrowing depth would significantly affect their vulnerability to fish foraging in the benthos, especially specialized benthivores such as catfish and carp. These are the two species that we expected to be excluded from the perforated treatments, and the significant reduction of the genus Tanypus in the control (open) as opposed to the two treatments (Table 2) suggests that larger benthivorous fish may be the cause of the reduced numbers. It is possible that the elevated numbers of corixids in perforated and closed treatments were a result of the insects crawling through the mesh in search of refuge from predation or wind generated currents. We measured several anatomical characters (including head capsule width) of corixids caught in perforated and closed cages and 76% of the individuals measured were first or second instars (which are small enough to fit through the mesh). However, the 9