Laboratory Evaluation of Hydrolox Screens 

December 2006 

Prepared By: 

Alden Research Laboratory, Inc. 

30 Shrewsbury Street 

Holden, MA 01520 

Prepared For: 

Intralox Inc. 

201 Laitram Lane 

Harahan, Louisiana 70123 
i

Table of Contents

Abstract........................................................................................................................................... v 

Introduction..................................................................................................................................... 1 

Experimental Design....................................................................................................................... 2 

Procedures....................................................................................................................................... 2 

Fish Holding Facility .................................................................................................................. 2 

Fish Marking............................................................................................................................... 3 

Test Procedures........................................................................................................................... 3 

Statistical Analysis.......................................................................................................................... 5 

Interpreting the Statistical Analysis............................................................................................ 6 

Results............................................................................................................................................. 8 

Golden Shiner ............................................................................................................................. 8 

Mortality ................................................................................................................................. 8 

Injury....................................................................................................................................... 8 

Scale Loss ............................................................................................................................... 8 

Common Carp........................................................................................................................... 12 

Mortality ............................................................................................................................... 12 

Injury..................................................................................................................................... 12 

Scale Loss ............................................................................................................................. 12 

Bluegill...................................................................................................................................... 15 

Mortality ............................................................................................................................... 16 

Injury..................................................................................................................................... 16 

Scale Loss ............................................................................................................................. 16 

Striped Bass .............................................................................................................................. 20 

Mortality ............................................................................................................................... 20 

Injury..................................................................................................................................... 20 

Scale Loss ............................................................................................................................. 21 

Channel Catfish......................................................................................................................... 24 

Mortality ............................................................................................................................... 24 

Injury..................................................................................................................................... 24 

Summary....................................................................................................................................... 27 

References..................................................................................................................................... 28 
ii

List of Tables 

Table 1 Total Number of Golden Shiner Live and Dead, Percent Mortality, and Mean Length by 

Treatment Condition ............................................................................................................... 9 

Table 2 Analysis of Maximum Likelihood Estimates for the Model of Mortality for Golden 

Shiner ...................................................................................................................................... 9 

Table 3 Total Number of Golden Shiner Injured and Not Injured, Percent Injury, and Mean 

Length by Treatment Condition............................................................................................ 10 

Table 4 Analysis of Maximum Likelihood Estimates for the Model of Injury for Golden Shiner

............................................................................................................................................... 10 

Table 5 Summary of Scale Loss Categories and Mean Length by Velocity Treatment for Golden 

Shiner .................................................................................................................................... 11 

Table 6 Analysis of Maximum Likelihood Estimates for the Scale Loss Regression Model for 

Golden Shiner ....................................................................................................................... 12 

Table 7 Total Number of Common Carp Live and Dead, Percent Mortality, and Mean Length by 

Treatment Condition ............................................................................................................. 13 

Table 8 Analysis of Maximum Likelihood Estimates for the Model of Mortality for Common 

Carp....................................................................................................................................... 13 

Table 9 Total Number of Common Carp Injured and Not Injured, Percent Injury, and Mean 

Length by Treatment Condition............................................................................................ 14 

Table 10 Analysis of Maximum Likelihood Estimates for the Model of Injury for Common Carp

............................................................................................................................................... 14 

Table 11 Summary of Scale Loss Categories and Mean Length by Velocity Treatment for 

Common Carp....................................................................................................................... 15 

Table 12 Analysis of Maximum Likelihood Estimates for the Scale Loss Regression Model for 

Common Carp....................................................................................................................... 15 

Table 13 Total Number of Bluegill Live and Dead, Percent Mortality, and Mean Length by 

Treatment Condition ............................................................................................................. 17 

Table 14 Analysis of Maximum Likelihood Estimates for the Model of Mortality for Bluegill . 17 

Table 15 Total Number of Bluegill Injured and Not Injured, Percent Injury, and Mean Length by 

Treatment Condition ............................................................................................................. 18 

Table 16 Analysis of Maximum Likelihood Estimates for the Model of Injury for Bluegill....... 18 

Table 17 Summary of Scale Loss Categories and Mean Length by Velocity Treatment for 

Bluegill.................................................................................................................................. 19 

Table 18 Analysis of Maximum Likelihood Estimates for the Scale Loss Regression Model for 

Bluegill.................................................................................................................................. 20 

Table 19 Total Number of Striped Bass Live and Dead, Percent Mortality, and Mean Length by 

Treatment Condition ............................................................................................................. 21 

Table 20 Analysis of Maximum Likelihood Estimates for the Model of Mortality for Striped 

Bass ....................................................................................................................................... 22 

Table 21 Total Number of Striped Bass Injured and Not Injured, Percent Injury, and Mean 

Length by Treatment Condition............................................................................................ 22 

Table 22 Analysis of Maximum Likelihood Estimates for the Model of Injury for Striped Bass 22 

Table 23 Summary of Scale Loss Categories and Mean Length by Velocity Treatment for Striped 

Bass ....................................................................................................................................... 23 
iii

Table 24 Analysis of Maximum Likelihood Estimates for the Scale Loss Regression Model for 

Striped Bass .......................................................................................................................... 24 

Table 25 Total Number of Channel Catfish Live and Dead, Percent Mortality, and Mean Length 

by Treatment Condition ........................................................................................................ 25 

Table 26 Analysis of Maximum Likelihood Estimates for the Model of Mortality for Channel 

Catfish ................................................................................................................................... 25 

Table 27 Total Number of Channel Catfish Injured and Not Injured, Percent Injury, and Mean 

Length by Treatment Condition............................................................................................ 26 

Table 28 Analysis of Maximum Likelihood Estimates for the Model of Injury for Channel 

Catfish ................................................................................................................................... 26 

Table 29 Summary of Mortality Rates by Treatment Condition .................................................. 27 

Table 30 Summary of Injury Rates by Treatment Condition ....................................................... 27 

Table 31 Summary of Scale Loss Rates by Treatment Condition................................................ 28 
iv

List of Figures 

Figure 1 Hydrolox Screen Installed in Fish Testing Flume............................................................ 1 

Figure 2 Hydrolox Screening Material ........................................................................................... 1 

Figure 3 Fish Holding Facility – Alden Research Laboratory........................................................ 3 

Figure 4 Steps Used in Interpreting the Hierarchical Results of the Logistic Regression Models. 7 

Figure 5 Histogram of Golden Shiner Fork Lengths ...................................................................... 9 

Figure 6 Distribution of Injury Types among Injured Golden Shiner .......................................... 11 

Figure 7 Histogram of Common Carp Fork Lengths.................................................................... 13 

Figure 8 Distribution of Injury Types among Injured Common Carp.......................................... 14 

Figure 9 Histogram of Bluegill Fork Lengths............................................................................... 17 

Figure 10 Distribution of Injury Types among Bluegill ............................................................... 19 

Figure 11 Histogram of Striped Bass Fork Lengths ..................................................................... 21 

Figure 12 Distribution of Injury Types among Striped Bass........................................................ 23 

Figure 13 Histogram of Channel Catfish Fork Lengths................................................................ 25 

Figure 14 Distribution of Injury Types among Channel Catfish .................................................. 26 
Hydrolox Screen Testing 

v

ABSTRACT

The modified traveling water screen is a fish protection technology option being considered by 

many thermal power generating facilities to reduce the mortality of juvenile and adult fish in 

compliance with Clean Water Act §316(b). The Hydrolox traveling screen is one type of 

modified screen that is being developed for this application at cooling water intake structures. 

The mortality, injury, and scale loss rates of five species of freshwater fish impinged and 

recovered with a Hydrolox screen were evaluated in the laboratory. Species tested included: 

golden shiner (Notemigonus crysoleucas), common carp (Cyprinus carpio), bluegill (Lepomis 

macrochirus), striped bass (Morone saxatilis), and channel catfish (Ictalurus punctatus). Fish 

were impinged at 1 or 2 ft/s velocity. During testing, the screen was rotated at either 5 ft/min or 

10 ft/min. Mortality, injury, and scale loss rates were generally low. For four of five species 

(golden shiner, common carp, bluegill, and channel catfish), mortality rates were less than 10% 

and, for most treatment conditions, were under 5%. Striped bass mortality was higher; however, 

control mortality was also higher, indicating that this population was sensitive to handling stress. 

Much of the mortality was likely not a direct result of exposure to Hydrolox screens. Observed 

rates of injury and scale loss were also low. 
Hydrolox Screen Testing 

1

INTRODUCTION

From July 24 to August 29, Alden Research Laboratory (Alden) conducted tests of a Hydrolox 

screen to determine its ability to collect and transfer fish with low mortality. Results are 

presented herein for golden shiner (Notemigonus crysoleucas), common carp (Cyprinus carpio), 

bluegill (Lepomis macrochirus), striped bass (Morone saxatilis), and channel catfish (Ictalurus 

punctatus). Tests were conducted in Alden’s Fish Testing Flume using a 4 ft wide by 12 ft high, 

fully operational Hydrolox screen installed perpendicular to the flow (Figure 1). Screening 

material was made of molded plastic with slot openings of 0.25 in. × 0.30 in. (Figure 2). 

Figure 1 

Hydrolox Screen Installed in Fish Testing Flume 

Figure 2 

Hydrolox Screening Material
Hydrolox Screen Testing 

2

EXPERIMENTAL DESIGN

The survival, injury, and scale loss of fish following impingement on a Hydrolox belt screen 

were evaluated. Five species of fish were impinged at two approach velocities (1 and 2 ft/s) and 

two screen rotation speeds (5 and 10 ft/min). For each species, 12 test replicates (2 velocities × 2 

screen speeds × 3 replicates of each condition) were collected. A randomized treatment design 

was used. On each day of testing, three, 2-hour treatments and one control replicate were 

conducted. Control replicates were used to separate mortality associated with handling (removal 

from holding facility, marking, counting into test groups, and introduction to and removal from 

the test flume) and natural mortality from mortality imparted by fish interactions with the 

screening system. 

PROCEDURES

Fish Holding Facility 

The fish holding facility consisted of a 20,820-liter (5,500-gallon) recirculating system (Figure 

3). Fish were held in one of eight cylindrical tanks, which drain into a central pool. Water was 

pumped through water treatment filters before returning to the holding tanks and completing the 

loop. Bag filters and an activated charcoal filter were used to remove particulates (solid waste 

material and other impurities). An ultraviolet light sterilizer and a fluidized bed (sand) bio-filter 

were used to control bacteria and soluble waste products. The holding facility was equipped 

with a five ton chiller to maintain water temperatures. Dissolved oxygen, temperature, and 

salinity were monitored. Salinity levels were maintained at approximately 5 ppt to reduce the 

occurrence of fungal growth common in freshwater aquaculture systems. Hardness, alkalinity, 

and ammonia levels were monitored weekly and chemically adjusted as needed. It was not 

possible to control temperatures within the testing facility, so holding facility temperatures were 

maintained within 2°C of the testing facility. 

A circular flow pattern was maintained in the fish holding tanks to keep fish active and reduce 

contact with the tank walls that could cause scale loss. Fish were fed age-, size-, and speciesspecific diets, which included dried brine shrimp, live Artemia sp., and solid commercially 

available fish chow. Fish physiology and behavior were qualitatively assessed daily to screen for 

external signs of disease, fungus, or infection by parasites. 
Hydrolox Screen Testing 

3

Figure 3 

Fish Holding Facility – Alden Research Laboratory

Fish Marking 

Fish in each release group were marked to allow their identification after recovery and to verify 

when they were released. At least 24 hours prior to testing, 300 treatment and 100 control fish 

(per species) were marked with dye. Compressed CO2 was used to inject biologically inert, 

micro-encapsulated, photonic dye at the base of individual fins. Four colors and three fin 

locations were used that provided 12 unique marks, so that each combination of color and fin 

location was used once per week. 

Test Procedures 

Tests were conducted in the following way: 

1. The screen rotation speed and approach velocity were set. The isolation screen that 

confined fish to the traveling screen area was lowered into place. 

2. During testing, observations of fish behavior were recorded using a tripod-mounted, 

hand-held, video camera focused through a glass viewing window in the side of the 

test flume. The first 15 minute period of most replicates was videotaped for potential 

future analysis. 

3. When conducting a treatment replicate, 100 fish of each species were introduced just 

upstream of the screen in the test enclosure. 
Hydrolox Screen Testing 

4

4. Impinged fish were washed from the screen into the fish collection trough. At set 

intervals of 15, 60, and 120 minutes after introduction to the flume, the fish were 

sluiced into a collection bucket located at the discharge of the return trough. 

5. When conducting a control replicate, 100 marked fish of each species were released 

into the fish return trough. Once the fish were oriented to the flow, they were sluiced 

into the collection bucket. 

6. Immediately following each collection, fish were observed and assigned to one of 

three categories: 

a. Live fish – swimming normally with no signs of injury, apparent orientation 

problem, or abnormal behavior. 

b. Stunned fish – struggling; swimming on side; floating belly-up but alive; and, 

bleeding or the presence of wounds, missing body parts, severe abrasions or 

lacerations. 

c. Dead fish – no vital signs, no body or opercular movement, no response to 

gentle probing. 

7. Live and stunned fish were held in net pens in the fish holding facility to assess latent 

impingement mortality (LIM). 

8. Following the 120 minute collection, a mechanical crowder was raised to move fish 

that were still swimming upstream of the screen into the screen buckets. Velocity in 

the flume was raised to 2 ft/s to facilitate the removal of larger fish. 

9. Fish that were entrained through the screen or bypassed the fish return during transfer 

were collected in a downstream collection net once per day at the end of testing, 

enumerated, and fork lengths (FL) measured to the nearest millimeter. 

10. At the end of each collection event, any fish recovered from the fish return trough 

(treatment or control replicate) were transferred back to the holding facility, placed in 

individually marked net pens, and held for LIM assessment. 

11. LIM was monitored at 24- and 48-hours following impingement. At the end of 48-

hours, all fish were killed and examined for external injuries and percent scale loss. 

External injuries were recorded by type: bruising/hemorrhaging, lacerations, severed 

body, eye damage, etc. Using methods similar to those reported by Neitzel et al. 

(1985) and Basham et al. (1982), percent scale loss (< 3%, 3–20%, 20–40%, and > 

40%) was recorded along the length of the body. All fish were measured for fork 

length to the nearest millimeter. Any fish unable to maintain equilibrium at 48-hours 

after testing was considered dead. 
Hydrolox Screen Testing 

5

STATISTICAL ANALYSIS

Analysis was conducted on those fish that were impinged and recovered from the fish return 

system. Entrained fish (i.e., those recovered in the downstream collection net) were not 

analyzed. In addition, fish collected in subsequent trials, which were exposed to multiple 

velocities and crowding events, were not included in the statistical analysis. Data were analyzed 

by logistic regression using SAS software (SAS Inst. 1999), as outlined below. 

Five possible independent variables were analyzed to determine their potential to impact 

mortality, injury and scale loss: 

1. approach velocity 

2. screen rotation speed 

3. collection time (15, 60, and 120 minutes after introduction and crowded fish) 

4. observation time (initial, 24-hours, and 48-hours) 

5. fork length 

Preliminary logistic regression models contained all five variables. However, the impingement 

responses were not sufficiently distributed over two of these variables (collection time and 

observation time) to allow a simultaneous analysis. In the case of collection time, fish tended to 

remain upstream of the screen until crowding at 1.0 ft/s. Conversely, at 2.0 ft/s, the majority of 

fish tended to be impinged and collected during the first 15 minutes. Thus, for any given 

velocity, the majority of fish fell into only one collection category. Similarly, very little 

mortality was observed during the initial and 24-hour observation periods. In all cases, this lack 

of differentiation between collection times and observation times prevented the logistic 

regression models from converging on reliable estimates. Therefore, the model design was 

reduced to include only velocity and fork length as variables. These logistic regression analyses 

for mortality and injury were implemented using the Logistic Procedure of the SAS software 

system (SAS Inst. 1999). 

The analysis for scale loss was based on an extension of logistic regression to a multiple category 

response variable (McCullagh and Nelder 1989) where the scale loss categories were strictly 

ordered: 1 = <3%; 2 = 3–20%; 3 = 20–40%; 4 = >40%. For each treatment, the distribution of 

observations among the categories can be viewed as a cumulative distribution. The probabilities 

predicted by the model are the cumulative probabilities of the scale loss categories : p1 = 

Pr(<=1) = Pr( = 1); p2 = Pr(<=2) = Pr( = 1 or 2); p3 = Pr(<=3) = Pr( = 1, 2 or 3); and p4 = 

Pr(<=4) = Pr( = 1, 2, 3 or 4) = 1.0. Note that p4 is by definition 1.0 and so the model need only 

predict the first three probabilities. The standard logistic model was formulated for each of these 

three probabilities: 
Hydrolox Screen Testing 

6

⎭

⎬

⎫

⎩

⎨

⎧ + +

+

+ + = ( 0 1 2(L )) 1 e ( 0 1 2(L )) p e

i j k i j k

ijk / β β β β β β

where: 

pijk = cumulative probability i, for treatment j, for fish k. 

β0i = an intercept value for the first three scale loss categories, i = 1, 2, 3. 

β1j = a parameter for each velocity, j = 1, 2, 3. The control is modeled by the 

intercept and this parameter models the offset from the control for each velocity 

treatment. 

β2 = a coefficient for the effect of length. 

Lk = fork length of fish k. 

In this model, the term β0 models the increase in probability from one cumulative probability to 

the next, and the β1 term models a shift of the cumulative distribution from one velocity 

treatment to the next. This feature causes the predicted probabilities for one velocity treatment to 

be proportional to the predicted probabilities for another. That is, there is a constant odds ratio 

across scale loss categories between a pair of velocity treatments. For this reason, this model is 

sometimes called the "proportional odds model." 

Interpreting the Statistical Analysis 

Species-specific results of the logistic regressions are presented in the following sections by 

species. There are separate discussions for each metric of performance (mortality, injury, and 

scale loss). Within each discussion of performance there are two statistical tables. The first table 

gives the raw frequencies and summary statistics by treatment condition and the second table 

gives a summary of logistic regression results. In some cases, there were too few mortalities, 

injuries, or scale loss to perform a meaningful logistic regression. This should be considered a 

positive affirmation of good screen performance. 

The first table is straight-forward and gives the frequency of live, dead (or injured, not injured, or 

level of scale loss), and total recovered for each velocity and rotation, as well as percent dead or 

injured and mean length. The second table for each species summarizes various estimates 

obtained from the logistic regression analyses. The first row(s) shows the intercept of the model, 

which is generally not of interest but is given for completeness. The next set of rows give 

estimates of the difference in logits between treatment conditions velocity and screen rotation 

speed and the control. The last three rows report: 1) the cumulative chi-square for all treatments; 

2) the coefficient of the covariate Fork Length; and 3) the cumulative chi-square for the full 

model (velocity, screen rotation treatments and fork length). In some cases, there was too little 

mortality or too few injuries for a successful logistic regress (i.e., the model failed to converge 

on a reliable estimate). 

The logistic regression models are hierarchical. A flow diagram showing the steps described 

below is shown in Figure 4. To interpret the significance of each component of the model (pvalue), one would start by looking at the full model (last row in each table). If the p-value for the 

full model was >0.05 then the model failed to converge on a reliable estimate and the fork length 
Hydrolox Screen Testing 

7

and velocity and rotation components of the model were not significant regardless of their pvalue. By contrast, if the p-value of the full model was significant (P<0.05), then the model 

converged upon a reliable estimate and it was appropriate to look at the velocity/rotation 

treatment and fork length components individually. A similar method would be used to look at 

the individual components of the model (see Figure 4). 

The scale loss regression tables are slightly different from those for injury and mortality. A 

positive coefficient of the estimated value means the probability in the lower levels of scale loss 

increase while a negative coefficient means the probability of lower levels of scale loss decreases 

and thus probability in the higher categories increases. 

Because these are cumulative probabilities, the intercept terms start negative and get 

progressively larger indicating increasing probability. Cumulative probability moving toward 

levels of greater scale loss must increase, because each cumulative probability includes the 

probability of the level of scale loss below. 

Velocity/Rotation

not 

significant

Velocity/

Rotation 

Effects

is p ≤ 0.05?

yes

no

Model

is p ≤ 0.05? Model is not 

no significant

yes

Length

is p ≤ 0.05? Length is not 

no significant

Length is

significant

yes

Individual 

Comparisons

1 ft/s - 5 ft/min

vs. control

2 ft/s - 5 ft/min

vs. control

1 ft/s - 10 ft/min

vs. control

is p ≤ 0.05?

Individual Velocity/ 

Rotation is 

Significant

Individual Velocity/ 

Rotation is 

not Significant

yes no

2 ft/s - 10 ft/min

vs. control

Velocity/Rotation

not 

significant

Velocity/

Rotation 

Effects

is p ≤ 0.05?

yes

no

Model

is p ≤ 0.05? Model is not 

no significant

yes

Model

is p ≤ 0.05? Model is not 

no significant

yes

Length

is p ≤ 0.05? Length is not 

no significant

Length is

significant

yes

Length

is p ≤ 0.05? Length is not 

no significant

Length is

significant

yes

Individual 

Comparisons

1 ft/s - 5 ft/min

vs. control

2 ft/s - 5 ft/min

vs. control

1 ft/s - 10 ft/min

vs. control

is p ≤ 0.05?

Individual Velocity/ 

Rotation is 

Significant

Individual Velocity/ 

Rotation is 

not Significant

yes no

2 ft/s - 10 ft/min

vs. control

Figure 4 

Steps Used in Interpreting the Hierarchical Results of the Logistic Regression Models 
Hydrolox Screen Testing 

8

RESULTS

Golden Shiner 

The golden shiner tested averaged 58.3 mm (FL) ± 3.9 (SD) and ranged from 40–73 mm. A 

histogram of lengths is shown in Figure 5. 

Mortality

Under all test conditions, a total of 32 fish died (2.3%). Mortality among the treatments ranged 

from 0.2% in the control treatment to 4.4% in the 2 ft/s velocity - 5 ft/min rotation treatment 

(Table 1). These differences are significantly different (P=0.0199; Table 2). The two treatments 

involving velocity of 2 ft/s have significantly greater mortality than controls while the 1 ft/s 

treatments do not (P=0.0042 for 2 ft/s velocity – 5 ft/min rotation treatment and P=0.0046 for 2 

ft/s velocity – 10 ft/min rotation treatment; Table 2). Mortality decreased as fish increased in 

length (P<0.0731; Table 2). 

Injury

Injury rates were relatively low. Injury rates ranged from 0.2% in the control to 4.1% in the 2 

ft/s velocity – 10 ft/min rotation treatment (Table 3). The regression model for golden shiner 

injury is only marginally significant (P=0.0672; Table 4), because there was so little mortality. 

The rates of injury between conditions were significant (P=0.0369; Table 4). The two treatments 

with 2 ft/s velocity were significantly greater than the controls (2 ft/s velocity – 5 ft/min rotation 

treatment; P=0.0171 and 2 ft/s velocity – 10 ft/min P=0.0047; Table 4). The most common 

injury type observed was bruising (77.8%), followed by lacerations (11.1%), fin damage (7.4%) 

and eye damage (3.7%) (Figure 6). 

Scale Loss

Observed scale loss was assigned into four discreet categories: 1) <3%; 2) 3–20%; 3) 20–40%; 

and 4) >40%. Scale loss for golden shiner was greater than the other species tested. For most 

treatment conditions, greater than half of the fish tested exhibited greater than 3% scale loss (

Table 5). Greater than 18% of tested fish in each treatment exhibited scale loss levels of 20% or 

greater (Table 5). Golden shiner are prone to scale loss as demonstrated by the levels of scale 

loss observed among control fish. More than 46% of the control golden shiner exhibited greater 

than 3% scale loss (Table 5). For golden shiner, there is a significant treatment effect 

(P<0.0001; Table 6). All treatments show significant differences from the control. For each 

treatment, the distribution is shifted toward higher levels of scale loss compared to the control. 

The coefficient for length is positive and significant (P=0.0135; Table 6), which suggests that 

larger fish tend to have less scale loss. 
Hydrolox Screen Testing 

9

Figure 5 

Histogram of Golden Shiner Fork Lengths 

Table 1 

Total Number of Golden Shiner Live and Dead, Percent Mortality, and Mean Length by Treatment 

Condition 

 Control 

1 ft/s velocity

5 ft/min 

rotation 

1 ft/s velocity

10 ft/min 

rotation 

2 ft/s velocity

5 ft/min 

rotation 

2 ft/s velocity 

10 ft/min 

rotation Total 

Live 450 142 139 324 283 1,338 

Dead 1 2 2 15 12 32 

Total 451 144 141 339 295 1,370 

Percent Dead 0.22 1.39 1.42 4.42 4.07 2.34 

Mean Length 58.44 58.85 57.65 58.36 58.44 

Table 2 

Analysis of Maximum Likelihood Estimates for the Model of Mortality for Golden Shiner 

 DF Estimate 

Standard 

Error 

Wald Chisquare Odds Ratio P-value 

Intercept 1 -1.376 2.7974 0.24 . 0.6228

(1 ft/s, 5 ft/min) vs Control 1 1.8516 1.2288 2.27 6.37 0.1318

(1 ft/s, 10 ft/min) vs Control 1 1.9035 1.2291 2.40 6.71 0.1214

(2 ft/s, 5 ft/min) vs Control 1 2.9693 1.0363 8.21 19.48 0.0042a

(2 ft/s, 10 ft/min) vs Control 1 2.9562 1.0438 8.02 19.22 0.0046a

Velocity/Speed Effects 4 . . 11.68 . 0.0199a

Fork Length 1 -.0819 0.0457 3.21 0.92 0.0731

Full Model 5 . . 15.52 . 0.0084a

a Statistically significant at P<0.05
Hydrolox Screen Testing 

10

Table 3 

Total Number of Golden Shiner Injured and Not Injured, Percent Injury, and Mean Length by 

Treatment Condition 

Control 

1 ft/s velocity

5 ft/min 

rotation 

1 ft/s velocity

10 ft/min 

rotation 

2 ft/s velocity

5 ft/min 

rotation 

2 ft/s velocity 

10 ft/min 

rotation Total 

Not Injured 450 142 139 330 283 1,344 

Injured 1 2 2 9 12 26 

Total 451 144 141 339 295 1,370 

Percent Injured 0.22 1.39 1.42 2.65 4.07 1.90 

Mean Length 58.44 58.85 57.65 58.36 58.44 

Table 4 

Analysis of Maximum Likelihood Estimates for the Model of Injury for Golden Shiner 

 DF Estimate 

Standard 

Error 

Wald Chisquare Odds Ratio P-value 

Intercept 1 -7.161 3.1757 5.08 . 0.0241 

(1 ft/s, 5 ft/min) vs Control 1 1.8466 1.2285 2.26 6.34 0.1328 

(1 ft/s, 10 ft/min) vs Control 1 1.8607 1.2288 2.29 6.43 0.1300 

(2 ft/s, 5 ft/min) vs Control 1 2.5215 1.0573 5.69 12.45 0.0171 

(2 ft/s, 10 ft/min) vs Control 1 2.9508 1.0436 7.99 19.12 0.0047 

Velocity/Speed Effects 4 . . 10.22 . 0.0369a

Fork Length 1 0.0179 0.0513 0.12 1.02 0.7265 

Full Model 5 . . 10.30 . 0.0672 

a Statistically significant at P<0.05
Hydrolox Screen Testing 

11

Figure 6 

Distribution of Injury Types among Injured Golden Shiner 

Table 5 

Summary of Scale Loss Categories and Mean Length by Velocity Treatment for Golden Shiner 

 Treatment 

Scale Loss Control 

1 ft/s 

velocity 

5 ft/min 

rotation 

1 ft/s 

velocity 

10 ft/min 

rotation 

2 ft/s 

velocity 

5 ft/min 

rotation 

2 ft/s 

velocity 

10 ft/min 

rotation Total 

<3% Frequency 243 44 53 173 80 593 

Percent 53.88 30.56 37.59 51.03 27.12 . 

3–20% Frequency 186 62 62 67 116 493 

Percent 41.24 43.06 43.97 19.76 39.32 . 

20–40% Frequency 21 21 15 69 63 189 

 Percent 4.66 14.58 10.64 20.35 21.36 . 

>40% Frequency 1 17 11 30 36 95 

 Percent 0.22 11.81 7.80 8.85 12.20 . 

Total Frequency 451 144 141 339 295 1,370 

Mean length 58.44 58.44 58.85 57.65 58.36 
Hydrolox Screen Testing 

12

Table 6 

Analysis of Maximum Likelihood Estimates for the Scale Loss Regression Model for Golden 

Shiner 

 DF Estimate

Standard 

Error 

Wald ChiSquare Odds 

Ratio P-value 

Intercept_1 1 -1.5646 0.76 4.24 . 0.0395a

Intercept_2 1 0.1431 0.76 0.04 . 0.8504 

Intercept_3 1 1.4444 0.76 3.59 . 0.0582 

(1 ft/s, 5 ft/min) vs Con 1 -1.0838 0.18 36.41 0.34 <0.0001a

(1 ft/s, 10 ft/min) vs Con 1 -0.7379 0.18 16.47 0.48 <0.0001a

(2 ft/s, 5 ft/min) vs Con 1 -0.5207 0.14 14.28 0.59 0.0002a

(2 ft/s, 10 ft/min) vs Con 1 -1.3073 0.14 83.16 0.27 <0.0001a

Treatment Effects 4 . . 93.65 . <0.0001a

Fork Length 1 0.0319 0.01 6.10 1.03 0.0135a

Full Model 5 . . 98.52 . <0.0001a

a Statistically significant at P<0.05

Common Carp 

The common carp tested ranged from 25–72 mm and averaged 35.9 mm (FL) ± 5.2 (SD). A 

histogram of lengths is shown in Figure 7. 

Mortality

Mortality among the treatments was 0.0% in all treatments except the 2 ft/s velocity – 10 ft/min 

rotation treatment, which had 0.5% mortality (

Table 7). Mortality rates were low and prevented meaningful regression analysis (P=0.8847; 

Table 8). 

Injury

Injury rates were also low (1.0% across all conditions tested; Table 9). Injury rates ranged from 

0.2% in the control to 4.1% in 1 ft/s velocity – 5 ft/min rotation treatment. Injury rates were too 

low to yield a meaningful regression (P=0.1056). Among the injured common carp, the most 

frequent injury types were: bruising (30.0%), fin damage (30.0%), and eye damage (20.0%) 

(Figure 8). 

Scale Loss

There was little scale loss among the common carp tested. Under all conditions, greater than 

82% exhibited the lowest level of scale loss (<3% of body surface). Among the treatments, the 

distribution of scale-loss is shifted toward higher levels as velocity increased (Table 11). For 

common carp, there was a significant treatment effect (P=0.0032; Table 12). Both treatments 

with 2 ft/s velocity showed significant differences from the control (P=0.0094 for the 5 ft/min 
Hydrolox Screen Testing 

13

rotation treatment and P=0.0003 for the 10 ft/min rotation treatment; Table 12). Length was not 

a significant predictor of scale loss (P=0.0835; Table 12). 

Figure 7 

Histogram of Common Carp Fork Lengths 

Table 7 

Total Number of Common Carp Live and Dead, Percent Mortality, and Mean Length by Treatment 

Condition 

Control 

1 ft/s velocity

5 ft/min 

rotation 

1 ft/s velocity

10 ft/min 

rotation 

2 ft/s velocity

5 ft/min 

rotation 

2 ft/s velocity 

10 ft/min 

rotation Total 

Live 414 73 70 215 198 970 

Dead 0 0 0 1 0 1 

Total 414 73 70 216 198 971 

Percent Dead 0.00 0.00 0.00 0.46 0.00 0.10 

Mean Length 33.79 36.66 36.16 37.10 36.57 

Table 8 

Analysis of Maximum Likelihood Estimates for the Model of Mortality for Common Carp 

DF Estimate 

Standard 

Error 

Wald Chisquare Odds Ratio P-value 

Intercept 1 2.7401 89.599 0.00 . 0.9756 

(1 ft/s, 5 ft/min) vs Con 1 -1.389 283.34 0.00 0.25 0.9961 

(1 ft/s, 10 ft/min) vs Con 1 -.8985 270.67 0.00 0.41 0.9974 

(2 ft/s, 5 ft/min) vs Con 1 9.2175 88.700 0.01 10071.66 0.9172 

(2 ft/s, 10 ft/min) vs Con 1 -.1073 176.38 0.00 0.90 0.9995 

Velocity/Speed Effects 4 . . 0.02 . 1.0000 

Fork Length 1 -.5344 0.4082 1.71 0.59 0.1905 

Full Model 5 . . 1.73 . 0.8847 
Hydrolox Screen Testing 

14

Table 9 

Total Number of Common Carp Injured and Not Injured, Percent Injury, and Mean Length by 

Treatment Condition 

Control 

1 ft/s velocity

5 ft/min 

rotation 

1 ft/s velocity

10 ft/min 

rotation 

2 ft/s velocity

5 ft/min 

rotation 

2 ft/s velocity 

10 ft/min 

rotation Total 

Not Injured 413 70 68 215 195 961 

Injured 1 3 2 1 3 10 

Total 414 73 70 216 198 971 

Percent Injured 0.24 4.11 2.86 0.46 1.52 1.03 

Mean Length 33.79 36.66 36.16 37.10 36.57 

Table 10 

Analysis of Maximum Likelihood Estimates for the Model of Injury for Common Carp 

 DF Estimate 

Standard 

Error 

Wald Chisquare Odds Ratio P-value 

Intercept 1 -7.289 2.0670 12.43 . 0.0004 

(1 ft/s, 5 ft/min) vs Con 1 2.9716 1.1708 6.44 19.52 0.0111 

(1 ft/s, 10 ft/min) vs Con 1 2.4631 1.2368 3.97 11.74 0.0464 

(2 ft/s, 5 ft/min) vs Con 1 0.6653 1.4169 0.22 1.95 0.6387 

(2 ft/s, 10 ft/min) vs Con 1 1.8333 1.1582 2.51 6.25 0.1134 

Velocity/Speed Effects 4 . . 8.89 . 0.0640 

Fork Length 1 0.0342 0.0483 0.50 1.03 0.4790 

Full Model 5 . . 9.09 . 0.1056 

Figure 8 

Distribution of Injury Types among Injured Common Carp 
Hydrolox Screen Testing 

15

Table 11 

Summary of Scale Loss Categories and Mean Length by Velocity Treatment for Common Carp 

 Treatment 

Scale Loss Control 

1 ft/s 

velocity 

5 ft/min 

rotation 

1 ft/s 

velocity 

10 ft/min 

rotation 

2 ft/s 

velocity 

5 ft/min 

rotation 

2 ft/s 

velocity 

10 ft/min 

rotation Total 

<3% Frequency 384 69 61 187 163 864 

Percent 92.75 94.52 87.14 86.57 82.32 . 

3–20% Frequency 22 2 7 19 32 82 

Percent 5.31 2.74 10.00 8.80 16.16 . 

20–40% Frequency 6 2 2 7 3 20 

 Percent 1.45 2.74 2.86 3.24 1.52 . 

>40% Frequency 2 0 0 3 0 5 

 Percent 0.48 0.00 0.00 1.39 0.00 . 

Total Frequency 414 73 70 216 198 971 

Mean length 36.57 33.79 36.66 36.16 37.10 

Table 12 

Analysis of Maximum Likelihood Estimates for the Scale Loss Regression Model for Common 

Carp 

 DF Estimate

Standard 

Error 

Wald ChiSquare Odds 

Ratio P-value 

Intercept_1 1 3.7238 0.71 27.32 . 0.0000 

Intercept_2 1 5.2877 0.74 51.52 . 0.0000 

Intercept_3 1 6.9183 0.84 68.00 . 0.0000 

(1 ft/s, 5 ft/min) vs Con 1 0.1909 0.55 0.12 1.21 0.7267 

(1 ft/s, 10 ft/min) vs Con 1 -0.5986 0.41 2.16 0.55 0.1419 

(2 ft/s, 5 ft/min) vs Con 1 -0.7127 0.27 6.75 0.49 0.0094a

(2 ft/s, 10 ft/min) vs Con 1 -0.9594 0.27 12.91 0.38 0.0003a

Treatment Effects 4 . . 15.89 . 0.0032a

Fork Length 1 -0.0319 0.02 2.99 0.97 0.0835 

Full Model 5 . . 19.61 . 0.0015a

a Statistically significant at P<0.05

Bluegill 

The bluegill tested ranged from 48–86 mm and averaged 59.5 mm (FL) ± 3.3 (SD). A histogram 

of lengths is shown in Figure 9. 
Hydrolox Screen Testing 

16

Mortality

Mortality rates for bluegill ranged from 1.0% among the control to 9.1% among the 1 ft/s 

velocity – 5 ft/min rotation treatment (Table 13). These differences were significant (P=0.0532; 

Table 14). The 1 ft/s velocity – 5 ft/min rotation treatment has significantly greater mortality 

than the control (P=0.0042; Table 14). While other treatments have greater mortality than the 

control, none are statistically significant. The majority of mortality at 1 ft/s velocity – 5 ft/min 

rotation treatment stemmed from a single treatment (17 of 19). Without this replicate, mortality 

would no longer be a significant predictor of mortality. Fork length appears to have a significant 

association (P<0.0001) of increasing mortality with increasing length, which is somewhat 

counterintuitive (Table 14). 

Injury

Injury rates among the treatments ranged from 2.3% in the control treatment to 21.8% in the 2 

ft/s velocity- 5 ft/min rotation treatment. These differences are significantly different (P<0.0001; 

Table 16). Each of the impingement treatments exhibited significantly greater mortality than the 

control (P≤0.0003; Table 16). Larger fish showed significantly fewer injuries (P<0.0063: Table 

16). Note this length effect is partly due to slightly longer length in the controls. Among injured 

bluegill, the most common injury types were scraping (82.1%) and bruising (7.4%; Figure 10). 

It should be pointed out that the majority of the scraping was minor and did not involve the loss 

of scales. 

Scale Loss

Scale loss levels were low for bluegill. The majority of fish (91% or greater under all 

conditions) fell into the lowest scale loss category (<3% of body surface). In addition, very few 

fish fell into the two higher scale loss categories (less than 1% under any condition; 

Table 17). Increases in velocity, shifted the distribution toward higher levels of scale loss. For 

bluegill, there is a significant treatment effect (P=0.0011; Table 18). Both treatments with 2 ft/s 

velocity show significant differences from the control (P=0.0030 for the 5 ft/min rotation 

treatment and P<0.0001 for the 10 ft/min rotation treatment; Table 18). Larger fish exhibited 

less scale loss (P<0.0165; Table 18). 
Hydrolox Screen Testing 

17

Figure 9 

Histogram of Bluegill Fork Lengths 

Table 13 

Total Number of Bluegill Live and Dead, Percent Mortality, and Mean Length by Treatment 

Condition 

Control 

1 ft/s velocity

5 ft/min 

rotation 

1 ft/s velocity

10 ft/min 

rotation 

2 ft/s velocity

5 ft/min 

rotation 

2 ft/s velocity 

10 ft/min 

rotation Total 

Live 383 190 241 255 263 1,332 

Dead 4 19 7 6 7 43 

Total 387 209 248 261 270 1,375 

Percent Dead 1.03 9.09 2.82 2.30 2.59 3.13 

Mean Length 60.43 59.62 59.23 59.24 59.24 

Table 14 

Analysis of Maximum Likelihood Estimates for the Model of Mortality for Bluegill 

DF Estimate 

Standard 

Error 

Wald Chisquare Odds Ratio P-value 

Intercept 1 -15.81 1.9894 63.14 . 0.0000 

(1 ft/s, 5 ft/min) vs Con 1 1.6895 0.5900 8.20 5.42 0.0042a

(1 ft/s, 10 ft/min) vs Con 1 0.8838 0.6374 1.92 2.42 0.1656 

(2 ft/s, 5 ft/min) vs Con 1 0.8125 0.6519 1.55 2.25 0.2127 

(2 ft/s, 10 ft/min) vs Con 1 0.9244 0.6332 2.13 2.52 0.1443 

Velocity/Speed Effects 4 . . 9.34 . 0.0532a

Fork Length 1 0.1879 0.0318 34.83 1.21 <0.0001a

Full Model 5 . . 57.91 . <0.0001a

a Statistically significant at P<0.05
Hydrolox Screen Testing 

18

Table 15 

Total Number of Bluegill Injured and Not Injured, Percent Injury, and Mean Length by Treatment 

Condition 

Control 

1 ft/s velocity

5 ft/min 

rotation 

1 ft/s velocity

10 ft/min 

rotation 

2 ft/s velocity

5 ft/min 

rotation 

2 ft/s velocity 

10 ft/min 

rotation Total 

Not Injury 378 190 208 204 214 1,194 

Injured 9 19 40 57 56 181 

Total 387 209 248 261 270 1,375 

Percent Injured 2.33 9.09 16.13 21.84 20.74 13.16 

Mean Length 60.43 59.62 59.23 59.24 59.24 

Table 16 

Analysis of Maximum Likelihood Estimates for the Model of Injury for Bluegill 

DF Estimate 

Standard 

Error 

Wald Chisquare Odds Ratio P-value 

Intercept 1 0.8397 1.7009 0.24 . 0.6215 

(1 ft/s, 5 ft/min) vs Con 1 1.4844 0.4150 12.79 4.41 0.0003a

(1 ft/s, 10 ft/min) vs Con 1 2.1193 0.3794 31.20 8.33 <0.0001a

(2 ft/s, 5 ft/min) vs Con 1 2.4694 0.3694 44.70 11.82 <0.0001a

(2 ft/s, 10 ft/min) vs Con 1 2.4025 0.3695 42.28 11.05 <0.0001a

Velocity/Speed Effects 4 . . 55.31 . <0.0001a

Fork Length 1 -.0776 0.0284 7.47 0.93 0.0063a

Full Model 5 . . 62.43 . <0.0001a

a Statistically significant at P<0.05
Hydrolox Screen Testing 

19

Figure 10 

Distribution of Injury Types among Bluegill 

Table 17 

Summary of Scale Loss Categories and Mean Length by Velocity Treatment for Bluegill 

 Treatment 

Scale Loss Control 

1 ft/s 

velocity 

5 ft/min 

rotation 

1 ft/s 

velocity 

10 ft/min 

rotation 

2 ft/s 

velocity 

5 ft/min 

rotation 

2 ft/s 

velocity 

10 ft/min 

rotation Total 

<3% Frequency 382 203 240 246 248 1,319 

Percent 98.71 97.13 96.77 94.25 91.85 . 

3–20% Frequency 5 5 8 12 21 51 

Percent 1.29 2.39 3.23 4.60 7.78 . 

20–40% Frequency 0 1 0 1 1 3 

 Percent 0.00 0.48 0.00 0.38 0.37 . 

>40% Frequency 0 0 0 2 0 2 

 Percent 0.00 0.00 0.00 0.77 0.00 . 

Total Frequency 387 209 248 261 270 1,375 

Mean length 59.24 60.43 59.62 59.23 59.24 
Hydrolox Screen Testing 

20

Table 18 

Analysis of Maximum Likelihood Estimates for the Scale Loss Regression Model for Bluegill 

DF Estimate

Standard 

Error 

Wald Chisquare Odds 

Ratio P-value 

Intercept_1 1 -2.3712 2.82 0.71 . 0.3999 

Intercept_2 1 0.1011 2.85 0.00 . 0.9717 

Intercept_3 1 1.0210 2.90 0.12 . 0.7246 

(1 ft/s, 5 ft/min) vs Con 1 -0.8650 0.61 1.99 0.42 0.1579 

(1 ft/s, 10 ft/min) vs Con 1 -0.9666 0.58 2.80 0.38 0.0941 

(2 ft/s, 5 ft/min) vs Con 1 -1.5533 0.52 8.82 0.21 0.0030a

(2 ft/s, 10 ft/min) vs Con 1 -1.9097 0.50 14.40 0.15 0.0001a

Treatment Effects 4 . . 18.25 . 0.0011a

Fork Length 1 0.1140 0.05 5.75 1.12 0.0165a

Full Model 5 . . 24.18 . 0.0002a

a Statistically significant at P<0.05

Striped Bass 

The striped bass tested ranged from 54–99 mm and averaged 77.5 mm (FL) ± 7.5 (SD). A 

histogram of lengths is shown in Figure 11. 

Mortality

Striped bass mortality was higher than the other species tested and ranged from 5.9% at 1 ft/s 

velocity – 10 ft/min rotation to 14.4% at 2 ft/s velocity – 5 ft/min rotation among the treatment 

conditions (Table 19). However, control mortality was also higher than other species tested 

(9.0%; Table 19). Mortality was also observed among the untested striped bass, held in the fish 

holding facility, during this same time period. Roughly 38% of the injuries observed during LIM 

observation were disease-related. Given the levels of observed mortality and disease among 

untested and control fish, it is safe to assume that much of the observed treatment mortality was 

associated with the poor physiological condition of the fish and not a direct result of exposure to 

the Hydrolox screen. Differences in treatment conditions were significantly different (P=0.0013; 

Table 20). Unlike other species, screen rotation speed appears to play an important role in 

mortality. The two treatments involving screen rotation of 5 ft/min have significantly greater 

mortality than controls, while the 10 ft/min rotation treatments are not significantly different 

from controls. Fork length does not appear to effect mortality (P=0.2639; Table 20). 

Injury

Injury rates among the treatments ranged from 3.2% in the 1 ft/s velocity - 5 ft/min rotation 

treatment to 10.6% in the 2 ft/s velocity- 10 ft/min rotation treatment (Table 21). These 

differences are significantly different (P=0.0048; Table 22). In the individual comparisons, only 

the 2 ft/s velocity- 10 ft/min rotation treatment differs significantly from the control (P=0.0011; 

Table 22). Longer fish had a greater probability of injury (P<0.0453), which is somewhat 
Hydrolox Screen Testing 

21

counterintuitive (Table 22). Injury types observed (in order of frequency) were: disease (38.6%), 

bruising (20.8%), fin damage (20.8%), scraping (17.8%), and lacerations (2.0%) (Figure 12). 

Scale Loss

Scale loss was nearly non-existent under any treatment or control condition (Table 23). There 

are no significant scale loss effects for smallmouth bass (Table 24). 

Figure 11 

Histogram of Striped Bass Fork Lengths 

Table 19 

Total Number of Striped Bass Live and Dead, Percent Mortality, and Mean Length by Treatment 

Condition 

Control 

1 ft/s velocity

5 ft/min 

rotation 

1 ft/s velocity

10 ft/min 

rotation 

2 ft/s velocity

5 ft/min 

rotation 

2 ft/s velocity 

10 ft/min 

rotation Total 

Live 354 183 225 185 180 1,127 

Dead 35 38 14 31 27 145 

Total 389 221 239 216 207 1,272 

Percent Dead 9.00 17.19 5.86 14.35 13.04 11.40 

Mean Length 77.40 75.60 76.94 75.73 77.16 
Hydrolox Screen Testing 

22

Table 20 

Analysis of Maximum Likelihood Estimates for the Model of Mortality for Striped Bass 

DF Estimate 

Standard 

Error 

Wald Chisquare Odds Ratio P-value 

Intercept 1 -3.350 0.9483 12.48 . 0.0004 

(1 ft/s, 5 ft/min) vs Con 1 0.7405 0.2515 8.67 2.10 0.0032a

(1 ft/s, 10 ft/min) vs Con 1 -.4423 0.3281 1.82 0.64 0.1777 

(2 ft/s, 5 ft/min) vs Con 1 0.5314 0.2630 4.08 1.70 0.0433a

(2 ft/s, 10 ft/min) vs Con 1 0.4363 0.2727 2.56 1.55 0.1097 

Velocity/Speed Effects 4 . . 17.94 . 0.0013a

Fork Length 1 0.0134 0.0120 1.25 1.01 0.2639 

Full Model 5 . . 19.49 . 0.0016a

a Statistically significant at P<0.05

Table 21 

Total Number of Striped Bass Injured and Not Injured, Percent Injury, and Mean Length by 

Treatment Condition 

Control 

1 ft/s velocity

5 ft/min 

rotation 

1 ft/s velocity

10 ft/min 

rotation 

2 ft/s velocity

5 ft/min 

rotation 

2 ft/s velocity 

10 ft/min 

rotation Total 

Not Injury 374 214 224 201 185 1,198 

Injured 15 7 15 15 22 74 

Total 389 221 239 216 207 1,272 

Percent Injured 3.86 3.17 6.28 6.94 10.63 5.82 

Mean Length 77.40 75.60 76.94 75.73 77.16 

Table 22 

Analysis of Maximum Likelihood Estimates for the Model of Injury for Striped Bass 

DF Estimate 

Standard 

Error 

Wald Chisquare Odds Ratio P-value 

Intercept 1 -5.760 1.3119 19.28 . 0.0000 

(1 ft/s, 5 ft/min) vs Con 1 -.2060 0.4661 0.20 0.81 0.6585 

(1 ft/s, 10 ft/min) vs Con 1 0.5661 0.3764 2.26 1.76 0.1325 

(2 ft/s, 5 ft/min) vs Con 1 0.6314 0.3761 2.82 1.88 0.0932 

(2 ft/s, 10 ft/min) vs Con 1 1.1373 0.3484 10.66 3.12 0.0011a

Velocity/Speed Effects 4 . . 14.96 . 0.0048a

Fork Length 1 0.0326 0.0163 4.01 1.03 0.0453a

Full Model 5 . . 17.83 . 0.0032a

a Statistically significant at P<0.05
Hydrolox Screen Testing 

23

Figure 12 

Distribution of Injury Types among Striped Bass 

Table 23 

Summary of Scale Loss Categories and Mean Length by Velocity Treatment for Striped Bass 

 Treatment 

Scale Loss Control 

1 ft/s 

velocity 

5 ft/min 

rotation 

1 ft/s 

velocity 

10 ft/min 

rotation 

2 ft/s 

velocity 

5 ft/min 

rotation 

2 ft/s 

velocity 

10 ft/min 

rotation Total 

<3% Frequency 385 220 235 211 204 1,255 

Percent 98.97 99.55 98.33 97.69 98.55 . 

3–20% Frequency 4 0 4 4 3 15 

Percent 1.03 0.00 1.67 1.85 1.45 . 

20–40% Frequency 0 1 0 1 0 2 

 Percent 0.00 0.45 0.00 0.46 0.00 . 

Total Frequency 389 221 239 216 207 1,272 

Mean Length 77.16 77.40 75.60 76.94 75.73 
Hydrolox Screen Testing 

24

Table 24 

Analysis of Maximum Likelihood Estimates for the Scale Loss Regression Model for Striped Bass 

DF Estimate

Standard 

Error 

Wald Chisquare Odds 

Ratio P-value 

Intercept_1 1 0.7084 2.41 0.09 . 0.7684 

Intercept_2 1 2.8654 2.49 1.32 . 0.2508 

(1 ft/s, 5 ft/min) vs Con 1 0.7948 1.12 0.50 2.21 0.4782 

(1 ft/s, 10 ft/min) vs Con 1 -0.4166 0.72 0.34 0.66 0.5601 

(2 ft/s, 5 ft/min) vs Con 1 -0.8258 0.68 1.49 0.44 0.2225 

(2 ft/s, 10 ft/min) vs Con 1 -0.2714 0.77 0.12 0.76 0.7251 

Treatment Effects 4 . . 2.93 . 0.5696 

Fork Length 1 0.0510 0.03 2.58 1.05 0.1079 

Full Model 5 . . 5.63 . 0.3443 

Channel Catfish 

The channel catfish tested ranged from 32–74 mm and averaged 50.7 mm (FL) ± 6.1 (SD). A 

histogram of lengths is shown in Figure 13. 

Mortality

Under all test conditions, only 1 fish died (0.1% at 1 ft/s velocity – 5 ft/min rotation; Table 25). 

There was not enough mortality for a meaningful logistic regression (P=0.9684; Table 26). 

Injury

Injury rates were also very low (Table 27). As with mortality, there was not enough injury for a 

meaningful logistic regression (P=0.5661; Table 28). Injury types observed (in order of 

frequency) were: eye injuries (33.3%), fin damage (33.3%), bruising (16.7%), and scraping 

(16.7%; Figure 14). 

Channel catfish do not have scales so rates of scale loss could not be calculated. 
Hydrolox Screen Testing 

25

Figure 13 

Histogram of Channel Catfish Fork Lengths 

Table 25 

Total Number of Channel Catfish Live and Dead, Percent Mortality, and Mean Length by Treatment 

Condition 

Control 

1 ft/s velocity

5 ft/min 

rotation 

1 ft/s velocity

10 ft/min 

rotation 

2 ft/s velocity

5 ft/min 

rotation 

2 ft/s velocity 

10 ft/min 

rotation Total 

Live 323 130 180 250 252 1,135 

Dead 0 1 0 0 0 1 

Total 323 131 180 250 252 1,136 

Percent Dead 0.00 0.76 0.00 0.00 0.00 0.09 

Mean Length 51.93 49.74 50.05 50.29 51.56 

Table 26 

Analysis of Maximum Likelihood Estimates for the Model of Mortality for Channel Catfish 

DF Estimate 

Standard 

Error 

Wald Chisquare Odds Ratio P-value 

Intercept 1 46.445 69.073 0.45 . 0.5013 

(1 ft/s, 5 ft/min) vs Con 1 3.8578 35.286 0.01 47.36 0.9129 

(1 ft/s, 10 ft/min) vs Con 1 -6.423 61.876 0.01 0.00 0.9173 

(2 ft/s, 5 ft/min) vs Con 1 -2.315 59.765 0.00 0.10 0.9691 

(2 ft/s, 10 ft/min) vs Con 1 -2.134 59.182 0.00 0.12 0.9712 

Velocity/Speed Effects 4 . . 0.08 . 0.9992 

Fork Length 1 -1.451 1.5966 0.83 0.23 0.3635 

Full Model 5 . . 0.92 . 0.9684 
Hydrolox Screen Testing 

26

Table 27 

Total Number of Channel Catfish Injured and Not Injured, Percent Injury, and Mean Length by 

Treatment Condition 

Control 

1 ft/s velocity

5 ft/min 

rotation 

1 ft/s velocity

10 ft/min 

rotation 

2 ft/s velocity

5 ft/min 

rotation 

2 ft/s velocity 

10 ft/min 

rotation Total 

Not Injury 322 129 179 249 252 1,131 

Injured 1 2 1 1 0 5 

Total 323 131 180 250 252 1,136 

Percent Injured 0.31 1.53 0.56 0.40 0.00 0.44 

Mean Length 51.93 49.74 50.05 50.29 51.56 

Table 28 

Analysis of Maximum Likelihood Estimates for the Model of Injury for Channel Catfish 

DF Estimate 

Standard 

Error 

Wald Chisquare Odds Ratio P-value 

Intercept 1 -1.357 3.7492 0.13 . 0.7175 

(1 ft/s, 5 ft/min) vs Con 1 1.5752 1.2336 1.63 4.83 0.2016 

(1 ft/s, 10 ft/min) vs Con 1 0.4246 1.4249 0.09 1.53 0.7657 

(2 ft/s, 5 ft/min) vs Con 1 0.1328 1.4207 0.01 1.14 0.9255 

(2 ft/s, 10 ft/min) vs Con 1 -10.70 227.32 0.00 0.00 0.9625 

Velocity/Speed Effects 4 . . 2.38 . 0.6668 

Fork Length 1 -.0882 0.0741 1.41 0.92 0.2343 

Full Model 5 . . 3.88 . 0.5661 

Figure 14 

Distribution of Injury Types among Channel Catfish 
Hydrolox Screen Testing 

27

SUMMARY

Summaries of mortality, injury, and scale loss are presented in the following tables. Mortality 

rates were generally low. For four of five species (golden shiner, common carp, bluegill, and 

channel catfish), mortality rates were less than 9.1% and for most treatment conditions were 

under 5% (Table 29). Striped bass mortality was higher; however, control mortality was also 

higher, indicating that this population was sensitive to handling stress and that much of the 

observed treatment mortality was likely not from exposure to the Hydrolox screen. 

Injury rates were also low and ranged from 0.0% (for channel catfish in the 2 ft/s velocity – 10 

ft/min rotation treatment) to 21.8% (for bluegill in the 2 ft/s velocity – 5 ft/min rotation 

treatment)(Table 30). 

Scale loss for three species was very low (common carp, bluegill, and striped bass). Golden 

shiner, which are more susceptible to scale loss, exhibited higher levels of scale loss (Table 31). 

This susceptibility to scale loss is demonstrated by the fact that greater than 46% of the control 

golden shiner exhibited greater than 3% scale loss (Table 31). 

Table 29 

Summary of Mortality Rates by Treatment Condition 

 Percent Mortality 

Species 

Mean 

Length 

(mm) Control 

1 ft/s 

velocity 

5 ft/min 

rotation 

1 ft/s 

velocity 

10 ft/min 

rotation 

2 ft/s 

velocity 

5 ft/min 

rotation 

2 ft/s 

velocity 

10 ft/min 

rotation Total 

Golden Shiner 58.3 0.2 1.4 1.4 4.4 4.1 2.3 

Common Carp 35.9 0.0 0.0 0.0 0.5 0.0 0.1 

Bluegill 59.5 1.0 9.1 2.8 2.3 2.6 3.1 

Striped Bass 77.5 9.0 17.2 5.9 14.4 13.0 11.4 

Channel Catfish 50.7 0.0 0.8 0.0 0.0 0.0 0.1 

Table 30 

Summary of Injury Rates by Treatment Condition 

Percent Injury 

Species Control 

1 ft/s 

velocity 

5 ft/min 

rotation 

1 ft/s 

velocity 

10 ft/min 

rotation 

2 ft/s 

velocity 

5 ft/min 

rotation 

2 ft/s 

velocity 

10 ft/min 

rotation Total 

Golden Shiner 0.2 1.4 1.4 2.7 4.1 1.9 

Common Carp 0.2 4.1 2.9 0.5 1.5 1.0 

Bluegill 2.3 9.1 16.1 21.8 20.7 13.2 

Striped Bass 3.9 3.2 6.3 6.9 10.6 5.8 

Channel Catfish 0.3 1.5 0.6 0.4 0.0 0.4 
Hydrolox Screen Testing 

28

Table 31 

Summary of Scale Loss Rates by Treatment Condition 

 Percent Scale Loss 

Species 

Scale Loss 

Level Control 

1 ft/s 

velocity 

5 ft/min 

rotation 

1 ft/s 

velocity 

10 ft/min 

rotation 

2 ft/s 

velocity 

5 ft/min 

rotation 

2 ft/s 

velocity 

10 ft/min 

rotation 

Golden Shiner <3% 53.9 30.6 37.6 51.0 27.1 

 3–20% 41.2 43.1 44.0 19.8 39.3 

 20–40% 4.7 14.6 10.6 20.4 21.4 

 >40% 0.2 11.8 7.8 8.9 12.2 

Common Carp <3% 92.8 94.5 87.1 86.6 82.3 

 3–20% 5.3 2.7 10.0 8.8 16.2 

 20–40% 1.5 2.7 2.9 3.2 1.5 

 >40% 0.5 0.0 0.0 1.4 0.0 

Bluegill <3% 98.7 97.1 96.8 94.3 91.9 

 3–20% 1.3 2.4 3.2 4.6 7.8 

 20–40% 0.0 0.5 0.0 0.4 0.4 

 >40% 0.0 0.0 0.0 0.8 0.0 

Striped Bass <3% 99.0 99.6 98.3 97.7 98.6 

 3–20% 1.0 0.0 1.7 1.9 1.5 

 20–40% 0.0 0.5 0.0 0.5 0.0 

 >40% -- -- -- -- -- 

REFERENCES

Basham, L. R., M. R. Delarm, J. B. Athern, and S. W. Pettit. 1982. Fish Transportation Oversight 

Team Annual Report, FY 1981: Transport Operations on the Snake and Columbia Rivers. 

NOAA Technical Memorandum NMFS F/NNR-2. Environmental and Technical Services 

Division, Northwest Regional Office, National Oceanic and Atmospheric Administration, 

National Marine Fisheries Service, Portland, OR. 

McCullagh, P. and J. A. Nelder. 1989. Generalized Linear Models, 2nd. Ed. Chapman & Hall, 

New York. p511. 

Neitzel, D. A., M. C. Richmond, D. D. Dauble, R. P. Mueller, R. A. Moursund, C. S. Abernethy, 

G. R. Guensch, and G. F. Cada. 2000. Laboratory Studies on the Effects of Shear on Fish: Final 

Report. Prepared for the U.S. Department of Energy, DOE/ID-10822. 

SAS Institute. 1999. SAS OnLine Doc: SAS/STAT Users Guide, Version 8. SAS Institute, 

Cary, NC.