Particle retention by non-suspension-feeding cyprinid fishes

Insectivorous Sacramento squawfish (Ptychocheilus grandis) and omnivorous 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 flakes or adult Artemia. These fish species retained small numbers of microspheres, and significantly more brine shrimp cysts than microspheres. During a 10-min period, they swallowed all of the brine shrimp cysts from a volume of water equivalent to 1-15 times their body volume. Squawfish and roach do not possess the morphological features of the branchial apparatus and palate that are associated with suspension feeding in confamilial Sacramento blackfish (Orthodon microlepidotus). The brine shrimp cysts could have been trapped between squawfish and roach gill rakers, while the microspheres;as well as the brine shrimp cysts could have been retained on mucus-covered buccopharyngeal surfaces. These results suggest that non-suspension-feeding fish species may ingest small suspended particles routinely, with energetic and ecotoxicological implications that deserve further study.