PARTICLE RETENTION BY NON-SUSPENSION-FEEDING CYPRINID FISHES

Insectivorous Sacramento squawfish (Ptychocheilus grandis) and omnivor ous benthic-feeding California roach (Hesperoleucus symmetricus) were exposed to suspended styrene microspheres (31-90 mu m) or brine shrimp cysts (210-300 mu m) in the presence of finely crushed Tetramin flake s or adult Artemia. These fish species retained small numbers of micro spheres, and significantly more brine shrimp cysts than microspheres. During a 10-min period, they swallowed all of the brine shrimp cysts f rom a volume of water equivalent to 1-15 times their body volume. Squa wfish and roach do not possess the morphological features of the branc hial apparatus and palate that are associated with suspension feeding in confamilial Sacramento blackfish (Orthodon microlepidotus). The bri ne shrimp cysts could have been trapped between squawfish and roach gi ll rakers, while the microspheres;as well as the brine shrimp cysts co uld have been retained on mucus-covered buccopharyngeal surfaces. Thes e results suggest that non-suspension-feeding fish species may ingest small suspended particles routinely, with energetic and ecotoxicologic al implications that deserve further study.