Laboratory Evaluation of Modified Ristroph Traveling Screens for Protecting Fish at Cooling Water Intakes

Publication Date



bass, catfish, fish length, impingement, injuries, models, mortality, perch, predation, ristroph screens, descaling, screens, striped bass, sucker, survival, traveling screen, yellow perch

Publication place

Palo Alto, CA


Electric Power Research Institute


The survival, injury, and scale-loss rates of 10 species of freshwater fish impinged and recovered with a modified traveling screen were evaluated in the laboratory. Species tested included golden shiner (Notemigonus crysoleucas), fathead minnow (Pimephales promelas), white sucker (Catostomus commersoni), bigmouth buffalo (Ictiobus cyprinellus), channel catfish (Ictalurus punctatus), hybrid striped bass (Morone chrysops x M. saxatilis), bluegill (Lepomis macrochirus), largemouth bass (Micropterus salmoides), yellow perch (Perca flavescens), and freshwater drum (Aplodinotus grunniens). Fish were impinged at 1, 2, or 3 ft/sec velocity. Survival rates exceeded 95% for all species and velocities tested, indicating that this technology has the potential to meet the Phase II section 316(b) impingement mortality reduction standard. Non-parametric logistic regression models were used to investigate the effect of velocity and fish length on survival, injury, and scale-loss. Velocity was a significant factor in predicting the mortality of bluegill, but no other species (see Table below). With bluegill, there was significantly more mortality at 2 ft/sec than the control. Fish tested at 3 ft/sec also had more mortality than the control, but this increase was only marginally significant. (p = 0.0601). Bluegill, golden shiner, white sucker, and yellow perch exhibited a significant decrease in mortality associated with an increase in fish length. Injury rates were variable by species. The two species obtained from wild populations (fathead minnow and white sucker) exhibited higher injury rates, in both the test and control fish, than the other species tested. The distribution of injury types was dominated by fin damage (40.3%), bruising or hemorrhaging (29.7%), and disease or fungus (19.7%). The remaining 10.4% of observed injuries were comprised of predation (4.4%), eye damage (3.5%), lacerations or tears (2.3%) and severed bodies (0.2%). The majority of predation injury was observed among bluegill and fathead minnow. For these two species, separate logistic regression models including and excluding the predation-related injury were evaluated. Velocity was a significant factor in predicting injury in five of the 12 comparisons and length was a significant factor in predicting the injury rate in six of the 12 comparisons (see Table below). In all cases where length was significant, larger fish exhibited fewer injuries. Scale-loss exhibited the most consistent response across species. Logistic regression models established reliable estimates for six species. In all six cases, Velocity was a significant predictor if scale-loss (see Table below). The 2 and 3 ft/sec treatments showed significantly more scale-loss than the control, but the 1 ft/sec treatment did not in four of the six species exhibiting a velocity effect: bigmouth buffalo, bluegill, freshwater drum, and white sucker. Golden shiner exhibited significantly more scale-loss at all three velocity treatments compared to the control. Velocity effects were observed for fathead minnow at 1 ft/sec, but not at 2 or 3 ft/sec. In five of the six successful logistic regressions, length was a significant predictor of scale-loss. In all five cases, larger fish experiences less scale-loss. Additional tests were undertaken with three species of fish to assess the effect of longer durations of impingement on survival, injury, and scale-loss: channel catfish, fathead minnow, and golden shiner. Fish were impinged up to 10 minutes and mortality, injury, and scale-loss were low. With channel catfish, no mortality or injury were observed among the treatment fish. For fathead minnow, the mortality and injury logistic regression models were not significant. Scale-loss among fathead minnow increased significantly with increasing durations of impingement. The mortality of golden shiner increased with longer durations of impingement and decreased with increase d fish length. Among golden shiner, a substantial number of the control fish exhibited injury. Increasing durations of impingement did not increase injury rates when the control mortality was included in the analysis. When control fish were eliminated from the analysis, there was still no detectable increase in injury associated with duration of impingement. Injury rates decreased with increasing fish length. Among golden shiner, scale-loss increased with increased duration of impingement and decreased as fish increased in length. In respect to fathead minnow, the regression models of mortality and scale-loss were not significant. Scale-loss among fathead minnow increased with increasing duration of impingement.

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