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Fisheries Experiment Station

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Abstracts

Inexpensive PVC Egg-Eyeing Jar

Dana Dewey1 and Eric J. Wagner2

Abstract — A design is presented for building an inexpensive (US$ 35) egg jar from polyvinyl chloride (PVC) parts. The unit has been used successfully to eye rainbow trout (Oncorhynchus mykiss) eggs.

Evaluation of a new baffle design for solid waste removal from hatchery raceways

Wagner, E.J. 1993. Progressive Fish-Culturist 55:43-47.

Abstract—A modification of the baffle system presented by Boersen and Westers (1986) for low flows is presented. There were no differences in growth or in the parameters of the health-and-condition profile between rainbow trout, Oncorhynchus mykiss, held in raceways with or without baffles. Distribution of dissolved oxygen in the raceways was similar between controls and baffled raceways. Mortality was significantly higher in raceways without baffles (4.6%) than in baffled raceways (3.7%), although the strength of the association was weak. Observations of fish during midday indicated no agonistic behavior among the fish in either the control raceways or baffled raceways.

Assessment of Fin Erosion by Comparison of Relative Fin Length in Hatchery and Wild Trout in Utah

Thomas Bosakowski and Eric J. Wagner

Abstract — We measured all fins of 600 hatchery trout sampled form all 10 state fish hatcheries in Utah, and of wild fish sampled as controls comprising 58 rainbow trout (Oncorhynchus mykiss), 33 cutthroat trout (O.clarki), and 54 brown trout (Salmo trutta). A strong linear correlation was found between fin length and total body length (100-300 mm) for all fins of wild rainbow trout. ARelative fin length@ (fin length/total body length x 100) proved to be a useful comparative measure, as this statistic was not biased by fish length in the wild fish sampled (all slopes 0.01%). Interspecific comparison of wild rainbow, cutthroat, and brown trout showed slight but statistically significant differences in some fin lengths. In Interspecific comparisons, hatchery fish had significantly shorter (10-50%) rayed fins than wild fish. The dorsal fin was most severely eroded in rainbow and brown trout, followed by the pectoral, anal, ventral, and caudal fins. In cutthroat trout the pattern was the same except that pectoral fins had more extensive erosion than dorsal fins. No species was clearly more susceptible to fin erosion in hatcheries, but the Fish Lake-DeSmet strain of rainbow trout had significantly shorter fins than other rainbow trout strains.

A Survey of Trout Fin Erosion, Water Quality, and Rearing Conditions at State Fish Hatcheries in Utah

Thomas Bosakowski and Eric J. Wagner

Abstract — A total of 600 hatchery trout were examined for signs of fin erosion including rainbow trout Oncorhynchus mykiss, cutthroat trout O. clarki, brook trout Salvelinus fontinalis and brown trout Salmo trutta. A scoring system was used to evaluate erosion on all fins from 20 fish samples. Water quality and hatchery rearing variables were also determined for corresponding raceways or ponds. For rainbow trout groups (N =24), stepwise multiple linear regression was used to interpret the relationship between fin erosion and the other variables. These fish groups averaged between 92 and 243 mm in total length and no significant correlation was observed between length and a fin erosion index (r = 0.045). The best-fit regression model (adjusted R2 = 0.689) suggested that fin erosion was correlated with lower alkalinities, unnatural bottom substrates (concrete or steel), higher unionized ammonia levels, and higher fish densities. Despite significant variation between hatcheries, fin condition was significantly better in rainbow trout than in cutthroat trout in three of four hatcheries containing both species and the same substrate. Fin erosion in rainbow trout occurred primarily on dorsal fins, followed in order of decreasing severity, by pectoral, caudal, anal, and ventral fins.

Performance and Behavior of Rainbow Trout Reared in Covered Raceways

Eric J. Wagner and Thomas Bosakowski

Abstract — Rainbow trout (Oncorhynchus mykiss) were reared in outdoor concrete raceways either with or without plywood covers. Growth, feed coversion, and mortality were not significantly different between the two groups after 215 d. Autopsy-based health and condition variables were not significantly different between the two groups. Fin length measurements were also not significantly different, indicating no reduction in fin erosion due to rearing in covered raceways. Fin erosion was worst at the end of the study (mean fin indexes, 1.45 and 1.60), but signs of fin erosion also occurred in the first autopsy sample when the fish were about 10 g each (mean fin indexes, 0.8 and 1.0). In an outdoor observation tank, single fish were observed for 5 min. Preference for the covered end of the tank was evident among fish from both covered and uncovered raceways (P< 0.001) and did not differ between treatments. Observations were also made for four-fish groups over a 45-min period either in the presence of a stuffed eagle or without it. During the first 15 min, fish from covered raceways stayed under cover more frequently than fish from uncovered raceways when the eagle was present. No significant differences in cover preference between fish from cover or no-cover treatments were noted during the second and third 15-min periods or when all periods were pooled. There was a tendency for all groups to seek cover less frequently in each successive time period.

Evaluation of the absorption efficiency of the low head oxygenation system

Abstract—The Low Head Oxygenation System or LHO™ is a device recently patented for injection of oxygen or other gases into liqids, relying on serial reuse of oxygen through a series of chambers or stages. The device is especially suited for applications where the low hydraulic head limits the use of other oxygen injection devices. The LHO has recently been used to supersaturate water with oxygen for increased production of fish. In this study, the absorption efficiency of the LHO and nitrogen gas supersaturation concentrations were evaluated at five different oxygen gas to liquid ratios (G/L) ranging from 0.10 to 0.83% (0.40-3.20 g O2/min). The mean absorption efficiency of the LHOs ranged from 67.3 to 90.6%, peaking at a G/L of 0.20% (0.79 g O2/min). This oxygen flow corresponded to a mean dissolved oxygen concentration of 12-13 mg/liter entering the raceway. Absorption efficiency decreased as oxygen flows increased. Nitrogen gas saturation was inversely proportional to oxygen flow, and did not fall below 100% saturation until oxygen flows exceeded a G/L of 0.64% (2.50 g/min).

Physiological Stress Responses of Cutthroat Trout to Loading by Fish Pump, Conveyor, or Dip Net

Eric J. Wagner and Diane M. Driscoll

Abstract — The physiological stress response of cutthroat trout, Oncorhynchus clarki, to three methods of loading into truck tanks for transport was evaluated. All loading methods caused a significant decrease in chloride and increase in plasma cortisol levels, relative to the baseline sample of unstressed fish. Based on plasma chloride changes, the conveyor method appeared the least stressful to the fish, while fish pump and dip netting were not significantly different from each other. Differences in plasma cortisol responses suggest that the conveyor and dip net method were less stressful than the fish pump. Plasma glucose concentrations in the fish were not elevated after loading and did not differ among loading methods. Overall, the conveyor method was the least stressful method of loading, but the differences were not sufficient magnitude to preferentially use one method over another.

Experimental use of cobble substrates in concrete raceways for improving fin condition of cutthroat (Oncorhynchus clarki) and rainbow trout (O. mykiss)

Thomas Bosakowski, Eric J. Wagner

Abstract — In two separate experiments, Bear Lake cutthroat trout (Oncorhynchus clarki Utah) fingerlings and domesticated rainbow trout (O.mykiss) fingerlings were reared for 10 and 6 months, respectively, in concrete raceways with or without (controls) cobblestone bottoms. Health/Condition Profiles (HCPs) were performed bi-monthly on 20 fish per treatment. Both species showed significantly reduced fin erosion in cobble bottom raceways using fin scores from all 8 fins of individual fish. Relative fin lengths (%of body length) showed that significant shortening of fins of control fish occurred on caudal and both pectoral fins for cutthroat trout and for right pectoral, both ventral caudal, and anal fins of rainbow trout. Comparison of the two species for relative fin lengths and fin scores showed that fin erosion was much more severe in rainbow trout. Overall, cobble substrates reduced fin erosion for both species, suggesting that natural bottoms are better for rearing than concrete.

Performance and Oxygen Consumption for Rainbow Trout Reared at Two Densities in Raceways with Oxygen Supplementation

Scott A. Miller, Eric J. Wagner, and Thomas Bosakowski

Abstract — The effects of fish-rearing density on growth, health, feed conversion (weight of food fed/fish weight gain) and oxygen consumption were evaluated for rainbow trout (Oncorhynchus mykiss) reared in oxygen-supplemented raceways. Fish were raised in two lots during consecutive years for 205 and 215 d at beginning densities of 2.46 and 9.83 kg/m (year 1) and 2.48 and 9.94 kg/m (year 2). Growth in both years (0.20 g/d, and 0.23 g/d year 1; and 0.25 g/d and 0.38 g/d year 2; higher-density groups and controls, respectively) was less in the higher-density treatments, although the difference was significant only in year 2. Bimonthly fish-health and condition indices showed no consistent differences between treatments, with the exception of fin erosion and plasma protein. Fish in the higher-density treatments had significantly more fin erosion and lower mean plasma protein indices than controls in both years. Feed conversion and oxygen consumption did not differ significantly between higher-density and control treatments. Results indicated that higher densities associated with oxygen injection can increase production, despite a slight reduction in growth and the need for increased system supervision. The impact of increased fin erosion at higher densities should be considered in management programs. For example, the use of oxygen injection may be appropriate for put-and-take fishing programs, in which stocked fish are large enough to avoid most predators.

Ammonia Excretion by Rainbow Trout over a 24-Hour Period at Two Densities during Oxygen Injection

Eric J. Wagner, Scott A. Miller, and Thomas Bosakowski

Abstract — Ammonia and dissolved oxygen (DO) concentrations were measured at six times over a 24-h period in 1992 and 1993 in raceways containing two densities of rainbow trout (Oncorhynchus mykiss). Ammonia production was highly variable, with peak concentrations 136-490% higher than the lowest concentrations, which usually occurred just before dawn. The peaks were generally observed during daylight, but could not be accurately predicted by feeding time or time of day. Ammonia concentrations observed in this study were compared with levels predicted by published models or summarized in other studies. The ratios of ammonia concentrations in higher-density raceways to the mean ammonia concentration of the two control raceways ranged from 1.54 to 2.15, which were similar to the ratios of fish density (1.75 to 2.58; high density/mean control density), indicating that ammonia production, on a per fish basis, was the same at both densities. Ammonia should be measured several times during the day for greatest accuracy. One measurement should be taken prior to the first morning feeding, when ammonia concentrations are lowest. Concentrations of DO at the lower end of the raceways showed a diel variation; the greatest oxygen consumption occurred at feeding time (in anticipation of feeding) or during the first hour after feeding. The differences between the highest and lowest DO values were greater (133-329%) in raceways with higher densities of fish. The greater fluctuation in higher-density raceways underscored the importance of choosing the appropriate time (within the first hour after feeding) to monitor DO in order to maintain adequate oxygen flows.

Performance and behavior of cutthroat trout (Oncorhynchus clarki) reared in covered raceways or demand fed

Eric J. Wagner, David A. Ross, Douglas Routledge, Brian Scheer, Thomas Bosakowski

Abstract - Cutthroat trout (Oncorhynchus clarki utah) were reared in outdoor raceways with or without plywood cover. The same hand-fed controls for this experiment were also used to test the effects of demand feeding. Growth, feed conversion, and mortality did not differ (P^0.05) among the hand fed covered, hand-fed uncovered (control), and demand-fed groups after 256 days. Autopsy-based parameters were generally not significantly different among groups. However, hematocrit and the fat index were significantly higher in covered raceways after 166 days. The fin index was significantly lower in covered raceways on both Day 166 and 225. Pectoral fin erosion was significantly reduced in covered raceways relative to controls by Day 166, but did not differ by Day 225. Demand feeding did not improve fin condition. Observations of cover preference were made for four fish groups over a 45 min period, either in the presence of a stuffed eagle or without it. All groups significantly preferred cover, but there were no differences related to rearing under cover or the presence of a predator model. Covers did improve fin condition and fat levels of fish during early rearing, but the benefits were not sustained throughout the rearing period. Use of demand feeders did not produce tangible health or growth benefits, but did not negatively impact the fish either. Demand feeding reduced the labor required to feed the fish, but increased cleaning time.

History and Fluctuating Asymmetry of Utah Salmonid Broodstocks

Eric J. Wagner

Abstract — The level of potential inbreeding in Utah salmonid broodstocks was assessed by fluctuating asymmetry (FA) of five bilateral meristic characters. Counts were made of the following characters on the left and right sides of 40 fish: gill rakers on the lower first branchial arch, gill rakers on the upper first branchial arch, mandibular pores, pectoral fin rays, and pelvic fin rays. Data from state hatchery records for the last 20 years were examined for trends in development to the eyed stage, percent hatch, and percent cripples (deformity). A brief history of Utah broodstocks is also presented. The mean FA for each of the strains of five species varied from 1.25 (Sand Creek strain rainbow trout Oncorhynchus mykiss) to 3.15 (Bonneville cutthroat trout O. clarki utah), with no consistent differences among species. The meristic counts were variable, and the overlap made differentiation among strains and species based upon these counts impossible. From 1972 to 1993, percent survival to the eyed egg stage for most Utah hatchery strains did not follow any trend, except survival to the eyed egg stage for most Utah hatchery strains did not follow any trend, except for brook trout Salvelinus fontinalis (r = -0.712) and albino rainbow trout (r =0.457). Eggs stripped from wild stocks of lake trout S. Namaycush and kokanee (lacustrine sockeye salmon O. nerka) had significantly lower survival to the eyed stage and hatching success than eggs from hatchery broodstocks, except for brook trout and albino rainbow trout. Mean crippling rates ranged from 1.5% in kokanee to 6.6% in Strawberry Reservoir cutthroat trout O. clarki. Fluctuating-asymmetry, eyed-up, hatching, and deformity data indicated either low or no imbreeding in Utah broodstocks.

The Effects of Fry Rearing Density on Hatchery Performance, Fin Condition, and Agonistic Behavior of Rainbow Trout Oncorhynchus mykiss Fry

Eric J. Wagner, Steven S. Intelmann and M. Douglas Routledge

Abstract — Rainbow trout Oncorhynchus mykiss fry were reared four densities ranging from 10,800 to 43,926 fish/m (9.91 to 37.60 kg/m) during an initial feeding period of 35 d. Each of the four initial density treatments were then split into high (3,780 fish/m) and low (1,890 fish/m) density groups and reared in outdoor raceways for an additional 74 d. A necropsy-based general health and condition assessment indicated that hematocrit, plasma protein which decreased as the initial density increased at low densities. Other necropsy variables indicated normal, healthy fish. Agonistic behavior was assessed at 4, 9, and 13 wk of age by observing the number of aggressive chases in paired and group (five fish) trials. The number of chases generally increased with age, although the difference between 9 and 13 wk was variable. Feeding did not elicit more chases in this study except for 9-wk-old fry. Initial rearing density did not have an impact on the number of chases at 4 or 13 wk, but at 9 wk the number of chases increased with initial density for the group tests. Relative fin length measurements of all fins except the adipose indicated no combination of initial density and outdoor density was superior to another for reducing fin erosion. This study indicated that rainbow trout fry may be reared at initial densities approaching 44,000 fish/m (Piper density index of 1.1) without negatively affecting growth and fin condition or inducing higher levels of agonistic behavior later on.

Assessment of Demand Feeder Spacing on Hatchery Performance, Fin Condition, and Size Variation of Rainbow Trout Oncorhynchus mykiss

Eric J. Wagner, M. Douglas Routledge and Steven S. Intelmann

Abstract — Fingerling rainbow trout, Oncorhynchus mykiss, were fed for 133 d by one of three feeding methods: one demand feeder per 5.5 m of raceway, 2 demand feeders per 5.5 m of raceway, 2 demand feeders per 5.5 m of raceway, and hand-fed controls. Mean weight, total length, mortality, and feed conversion were not influenced by the method of feeding. Size variation did not differ among treatment groups, as assessed by comparing the coefficient of variation of total length. Necropsy-based health and condition profiles were conducted three times during the rearing period, and results indicated that fish were generally normal and healthy in all treatments. Several parameters differed significantly over time, but no trends were observed except for the fin index and hematocrit. Over time, hematocrit decreased form 48.6 to 45.0% and the fin index increased from 0.80 to 1.57. Fin index values did not differ among the feeding methods. Fin condition assessed by measuring relative fin length was better in the single feeder treatment than controls for caudal and ventral fins in the last sample. However, since fish from the two-feeder treatment did not differ from controls, demand feeding per se did not improve fin condition relative to fish that were fed by hand, for to six times per day. The lack of significant improvements in growth of health with the addition of another demand feeder indicated that using more than one feeder per 5.5 m of raceway length is unnecessary for culture of juvenile rainbow trout.

Fin Condition and Health Profiles of Albino Rainbow Trout Reared in Concrete Raceways with and without a Cobble Substrate

Eric J. Wagner, M. Douglas Routledge, and Steve S. Intelmann

Abstract — Fingerlings of albino rainbow trout Oncorhynchus mykiss were reared for 200 din concrete raceways with either concrete (controls) or cobblestone bottoms. Health and condition profiles were performed on 20 fish/treatment on four occasions. For fish in cobble-bottom raceways, there was no fin erosion as measured by fin indices (ranked from 0 to 2) applied to the fish as a whole or relative fin lengths (% of body length) of individual fins. For control fish, however, considerable erosion was evident for caudal, dorsal, anal, both pectoral, and both ventral fins. Condition factor, fat levels, and total length were reduced in cobbled raceways. Results are compared with previous experiments with normally pigmented rainbow and cutthroat trout O. clarki. Overall, cobble substrates markedly reduced fin erosion, which suggests that cobble-bottom raceways are especially suitable for rearing albino rainbow trout, if a slight reduction in growth is acceptable.

The Toxicity of Hydrogen Peroxide to Rainbow Trout Oncorhynchus mykiss and Cutthroat Trout Oncorhynchus clarki Fry and Fingerlings

Ronney E. Arndt and Eric J. Wagner

Abstract — Fungal and parasitic infections of fish can significantly impact the survival of cultured fish. Formalin is currently used to control such infections; however, concern has arisen over its safety to users and to the environment. Hydrogen peroxide has been designated as a low priority fungicidal drug by the United States Food and Drug Administration (FDA), yet little information is available on treatment concentrations or its toxicity to trout. Rainbow trout Oncorhynchus mykiss and cutthroat trout Oncorhynchus clarki fry and fingerlings were exposed to hydrogen peroxide concentrations of 0, 70, 170, 280, 420, and 540 ppm for 30, 60 or 120 min at 15 C to determine the chemical's toxicity. Rainbow trout fry and fingerlings experienced elevated mortalities (>20%) during treatments using 420 and 540 ppm for 30 min; 280, 420, and 540 ppm for 60 min; and _>170 ppm for 120 min. Cutthroat trout fry experienced elevated mortalities (>23 percent) during treatments using 540 ppm for 30 min; 420 and 540 ppm for 60 min; and _>170 ppm for 120 min. Cutthroat trout fingerlings experienced elevated mortalities (>60%) during treatments using 540 ppm for 60 min and _>280 ppm for 120 min. No control mortalities were encountered for both life stages for either species. The lethal concentrations (LC 50) of both age classes and species for each of the three durations ranged from 514-636 ppm for 30 min treatments, 322-506 ppm for 60 min treatments, and 189-280 for 120 min treatments. Mortalities for all four toxicity tests which occurred during a 96-h post-treatment period were centered around the following treatments: 30 min, 540 ppm; 60 min, 280-540 p.m.; 120 min, 170 p.m.. Tissue damage to gills was found only among fish that did not survive the initial chemical exposure. Test concentrations proved to be relatively stable during a 24-h period, retaining better than 85% of their original strength for all five dilutions. At a water temperature of 15 C concentrations should not exceed 280 p.m. for a 30-min treatment.

Effects of Rearing Density upon Cutthroat Trout Hematology, Hatchery Performance, Fin Erosion, and General Health and Condition

Eric J. Wagner, Tim Jeppsen, Ronney Arndt, M. Douglas Routledge and Quentin Bradwisch

Abstract — Cutthroat trout of the Bear Lake Bonneville strain, Oncorhynchus clarki utah, were used in two separate density experiments. In the first, fish were reared for 212 d in outdoor raceways at four densities; fish were allowed to grow into their final rearing density and were fed 7d/week. Final rearing densities averaged 768, 1.597, 2,073, and 2,998 fish/m, and corresponding density indices (DI = fish weight, lb/[fish length, in x water volume, ft])were 0.40, 0.90, 1.10, and 1.46. In experiment 2, crowding screens were adjusted monthly, and fish ere fed 5 d/week; final rearing densities were 338, 739, and 1.634 fish/m (DIS of 0.19, 0.39, 0.75). Feed conversion and mortality did not significantly differ among densities for either experiment. Final mean weights did not differ among the four densities of experiment 1, but mean total length was significantly longer in fish reared at the lower densities. In experiment 2, final mean weight was significantly reduced in the highest density and specific growth rates for all densities were lower than in experiment 1. Frequencies of agonistic behaviors did not differ among densities in experiment 2. Hemoglobin, total white blood cell (WBC) counts, differential WBC counts, and hepatosomatic indices did not differ among densities in either experiment. Red blood cell (RBC) counts and the splenosomatic index (SI) did not differ among densities of experiment 1. However, in experiment 2, the RBC count was higher at the lowest density than at the highest, and the SI was significantly higher at the highest density than the lowest. Condition factor, plasma protein, hematocrit, and relative dorsal fin length differences among densities were observed, but were inconsistent over time. Adverse effects of high density on mesenteric fat levels and pectoral fin condition were observed in experiment 2. Saltwater challenge tests resulted in greater mortality for fish from high densities. The data indicated that rearing cutthroat trout at a DI of 0.75 or higher (about 1,600 fish/m) may compromise fish health when densities are adjusted monthly and fish are fed 5 d/w; the data also indicated that even lower densities are needed for maximum growth.