Ronney E. Arndt

Physiological stress responses, egg survival and sperm motility for rainbow trout broodstock anesthetized with clove oil, tricaine methanesulfonate or carbon dioxide

Abstract Egg survival, sperm motility and physiological stress responses (plasma cortisol, glucose and chloride) of rainbow trout ( Oncorhynchus mykiss ) broodstock were compared among three anesthetics: tricaine methanesulfonate (MS-222), clove oil in the form of AQUI-S® (a proprietary mix of 50% isoeugenol and other ingredients) and carbon dioxide gas. Concentrations of 60 mg/l tricaine, 20 mg/l isoeugenol (40 mg/l AQUI-S) and 220–275 mg/l carbon dioxide were based on preliminary tests and chosen to standardize induction time among anesthetics. Plasma glucose, chloride and cortisol concentrations indicated that none of the anesthetics used after crowding and netting completely eliminated the stress response. The return to prestress cortisol levels differed among the three anesthetics. Fish anesthetized with AQUI-S had significantly lower cortisol concentrations at 1 or 7 h postimmersion than the other anesthetics and controls, but were elevated at 24 h. Plasma cortisol in tricaine- and CO 2 -treated fish returned to prestress levels within 7 and 24 h, respectively, whereas cortisol levels in control fish remained elevated at 24 h. Sperm motility and duration of motility were assessed for a practical range of concentrations: tricaine, 15–100 mg/l; AQUI-S, 10–100 mg/l; CO 2 , 50–173 mg/l. The percentage of motile sperm was unaffected by anesthetic treatment, averages ranging from 68% to 87%. However, duration of motility decreased as anesthetic concentration increased, averages ranging from 55 to 36 s for tricaine and from 56 to 37 s for AQUI-S. Duration of sperm motility was low (31–43 s) for all levels of CO 2 tested. Fish recovery time was significantly longer for fish anesthetized by AQUI-S (370 s) than the either CO 2 or tricaine (192 and 199 s, respectively). Gender had no effect on recovery time. Egg survival to the eyed stage and to hatch was not significantly different among anesthetic treatments and controls. No delayed mortality was observed for any of the fish handled and bled for the test. Results indicated that tricaine, AQUI-S and CO 2 were all suitable for broodfish anesthesia, but the longer recovery time and lower cost for AQUI-S may make it more useful than the alternatives. None of the anesthetics wholly suppressed the stress responses during a typical spawning process, but did help reduce the duration of the stress responses and eased handling without compromising egg viability.

Reducing or Withholding Hydrogen Peroxide Treatment during a Critical Stage of Rainbow Trout Development: Effects on Eyed Eggs, Hatch, Deformities, and Fungal Control

Abstract In two separate trials, eggs of rainbow trout Oncorhynchus mykiss were cultured with the use of hydrogen peroxide and formalin treatments to control fungal infections. For the first trial, treatment regimens consisted of no chemical treatment (control) or daily treatments of either hydrogen peroxide at 500 mg/L for 35 min or formalin at 1,667 mg/L for 15 min. Hydrogen peroxide treatment duration was reduced to 5 min daily during 70–140 daily temperature units (DTU°C). In this trial, 27% of control eggs were infected with fungus, compared with 0% for the hydrogen peroxide and formalin treatments. Eyed egg percentages were significantly lower for control eggs compared with the hydrogen peroxide and formalin treatments. Comparing formalin and hydrogen peroxide treatments, percent hatch at 91% and 90% and percent deformities at 1.0% and 1.3%, respectively, were not significantly different. In the second trial, rainbow trout eggs were reared from fertilization to hatch under four treatment regiments: ...

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

Abstract Ahstract.—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 7 d/week. Final rearing densities averaged 768, 1,597, 2,073, and 2,998 fish/m3, and corresponding density indices (DI = fish weight, Ib/[fish length, in ×water volume, ft3]) were 0,40, 0.90, 1.10, and 1,46. In experiment 2, crowding screens were adjusted monthly, and fish were fed 5 d/week: final rearing densities were 338, 739, and 1,634 fish/m3 (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...

Comparison of the Efficacy of Iodine, Formalin, Salt, and Hydrogen Peroxide for Control of External Bacteria on Rainbow Trout Eggs

Abstract Two experiments were conducted in vivo with eggs of rainbow trout Oncorhynchus mykiss to compare the bactericidal ability of four common disinfectants. A third test compared bacterial abundance estimation methods for fish eggs (use of a vortex mixer for agitating an egg versus rolling the egg across a petri dish). In the first test, the number of colony forming units (CFU) counted on enriched Ordahls agar with tobramycin (EOT) or trypticase soy agar (TSA) was compared among eggs treated with various doses of iodine, hydrogen peroxide, formalin, or rock salt. A treatment of 1,667 mg of formalin/L of water and all iodine, salt, and hydrogen peroxide treatments had significantly fewer bacteria on EOT than did controls, but CFU counts for a formalin treatment of 500 or 1,000 mg/L did not. All chemical treatments significantly reduced CFU counts on TSA relative to controls except salt at 0.030 mg/L and formalin at 500 mg/L. The least growth was observed on iodine-treated eggs. In the second experimen...

Comparison of Hatchery Performance, Agonistic Behavior, and Poststocking Survival between Diploid and Triploid Rainbow Trout of Three Different Utah Strains

Abstract The hatchery performance (growth, feed conversion, and survival) of rainbow trout Oncorhynchus mykiss was compared between diploid and triploid fish from three Utah strains: Fish Lake-DeSmet (FD), Sand Creek (SC), and Ten Sleep (TS). For FD, specific growth rates were slightly higher for triploids (2.79%/d) than for diploids (2.60%/d), but final mean weight at 108 d did not significantly differ. For SC and TS, there were no significant differences in final mean weight or specific growth rates after 138 or 122 d, respectively. Feed conversion ratios and fish mortality in the raceways did not differ significantly between diploids and triploids, except for SC for which mortality rates were slightly higher for triploids (4.0%) than diploids (2.1%). Possible differences in agonistic behavior between diploids and triploids were assessed by video observation of size-matched pairs (diploid-diploid, diploid-triploid, or triploid-triploid). There were no significant differences between diploid and triploid...

Comparison of susceptibility of five cutthroat trout strains to Myxobolus cerebralis infection

Abstract Susceptibility to infection by the myxosporean parasite Myxobolus cerebralis was compared among strains of cutthroat trout Oncorhynchus clarki in two separate exposure tests in the laboratory. In both tests, each strain was exposed to 1,000 triactinomyxons/fish for 2 h in 8.0 L of water. In the first test, three strains of 10-week-old cutthroat trout were compared: two strains of Bonneville cutthroat trout O. c. utah (Bear Lake and southern Bonneville strains) and Yellowstone cutthroat trout O. c. bouvieri. In the second test, these strains plus Snake River fine-spotted cutthroat trout O. c. subsp. and Colorado River cutthroat trout O. c. pleuriticus were exposed at either 5 or 10 weeks of age. The prevalence of the M. cerebralis infection was determined by single-round polymerase chain reaction (PCR) assay 5 weeks after exposure. In the first test, the prevalence was significantly lower in the Bear Lake strain of Bonneville cutthroat trout (78.5%) than in the Yellowstone (97.8%) or southern Bonn...

Influence of Raceway Substrate and Design on Fin Erosion and Hatchery Performance of Rainbow Trout

Abstract Raceway substrate and design were manipulated in a series of four trials to improve fin condition of rainbow trout Oncorhynchus mykiss. In the first trial, fish were reared in either conventional concrete raceways or raceways fitted with a false floor overlaid with cobble and through which water and waste materials flowed. Growth, feed conversions, and mortalities were not influenced by treatment type, but fish reared in false-floor raceways exhibited an improvement in fin lengths. For trial 2, fish were raised in control raceways or raceways that contained two-dimensional, painted gravel patterns (2D) as a substrate or actual gravel affixed to the raceway bottom (3D) to provide a three-dimensional appearance. Growth, feed conversions, and mortalities were not influenced by treatment type, but fish in the 3D treatment had significantly better dorsal fins compared with the control and 2D groups. Anal fins, pelvic fins, and right pectoral fins were significantly better for control and 3D fish compa...

The Safety and Effectiveness of Various Hydrogen Peroxide and Iodine Treatment Regimens for Rainbow Trout Egg Disinfection

Abstract Four tests were conducted to evaluate iodine and hydrogen peroxide for the disinfection of rainbow trout Oncorhynchus mykiss eggs at higher doses for shorter durations than previously studied. In the first test, eyed eggs were exposed to (1) 2,000 mg iodine/L for 10 min, (2) 100 mg iodine/L for 15 min, (3) 30 g hydrogen peroxide/L for 1 min, (4) 6 g hydrogen peroxide/L for 5 min, or (5) no treatment. Iodine (2,000 mg/L) or hydrogen peroxide (30 g/L) significantly reduced bacterial loads on eggs but did not significantly affect egg survival or fry deformity rates. Hydrogen peroxide at 30 g/L for 1 min was generally better for bacterial control than the other treatments, but the 2,000-mg/L iodine treatment also was effective. A second test assessed the effect of hydrogen peroxide on pH at various levels of water hardness. The pH of hydrogen peroxide solutions dropped as total hardness levels decreased, but buffering with at least 1.32 g NaHCO3/L returned pH to approximately neutral levels. In the t...

Evaluation of Disease Resistance of the Fish Lake–DeSmet, Wounded Man, and Harrison Lake Strains of Rainbow Trout Exposed to Myxobolus cerebralis

Abstract Several tests evaluated the whirling disease resistance of three stocks of rainbow trout Oncorhynchus mykiss: the Fish Lake–DeSmet (FD), Wounded Man (WM), and Harrison Lake (HL) strains. In one series, FD fish were exposed to Myxobolus cerebralis triactinomyxons (TAMs; one exposure of 1,000 TAMs/fish). Histological scores ranged from 4.28 to 4.95 (MacConnnell−Baldwin scale) among FD fish from three different hatcheries. In addition, FD fish were exposed either acutely (1,000 TAMs/fish in one dose) or chronically (100 or 200 TAMs/fish on each of 10 d). There was no significant difference in mean myxospore counts among the three different exposure treatments. Histological scores ranged from 3.76 to 3.86 among the exposure groups and did not differ among exposure treatments. The correlation between histological scores and myxospore counts was significant (r = 0.57). Three different ages of WM rainbow trout were challenged with 1,000 TAMs/fish; histological scores for 62-d-old fish were significantly...

Reproductive Ecology and Spawning Substrate Preference of the Northern Leatherside Chub

Abstract Conservation of rare fishes is often hindered by a lack of understanding of their basic life history characteristics. We used captive-breeding studies to determine the preferred spawning habitat and early life history characteristics of the northern leatherside chub Lepidomeda copei, a small cyprinid native to the upper Snake River basin and the Bear River drainage in the Bonneville Basin (Idaho, Utah, and Wyoming). In the first study, wild adult northern leatherside chub were given a choice of four habitats (two shallow riffle habitats and two deeper pool habitats), each with four spawning substrates (large cobble, small cobble, pebble, and a coarse artificial spawning mat) in a large rectangular tank. In the second study, adults were given a choice of three locations with different water velocities (9.5, 12.9, or 19.0 cm/s) but the same substrate size (small cobble). Successful spawning occurred in both studies. Northern leatherside chub spawned almost exclusively over the small cobble substrat...