M. Douglas Routledge

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 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...

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...

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

Abstract Fingerlings of albino rainbow trout Oncorhynchus mykiss were reared for 200 d in 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.

Comparison of Hatchery and Field Performance between a Whirling-Disease-Resistant Strain and the Ten Sleep Strain of Rainbow Trout

A whirling-disease-resistant strain of rainbow trout Oncorhynchus mykiss (GRHL strain) derived from a backcross of an F1 hybrid of two strains (German strain x Harrison Lake strain) with German strain females, was compared with the Ten Sleep (TS) strain of rainbow trout. The GRHL strain had consistently superior growth and feed conversion in two consecutive hatchery trials. Hatching and mortality rates were similar between strains. Both strains were stocked into two Utah reservoirs (Hyrum, Porcupine), and a third, Causey Reservoir, was monitored as a control for seasonal variation in prevalence of Myxobolus cerebralis. A total of 1,323 salmonids captured by gill net in spring and fall sampling between 2006 and 2008 were tested for M. cerebralis via pepsin-trypsin digest methods. Only eight of these (< 1% per species) had clinical signs consistent with whirling disease. In both reservoirs, GRHL survived better than the TS and had higher growth rates. The prevalence of M. cerebralis was significantly lower for GRHL (18.1%) than TS (50.0%) in Porcupine Reservoir. In Hyrum Reservoir the trend was similar, but prevalence was lower and did not significantly differ between GRHL (9.6%) and TS (23.1%). For infected fish, no significant differences were observed between strains in myxospore counts in either Hyrum (GRHL = 911-28,244 spores/fish [spf], TS = 1,822-155,800 spf) or Porcupine (GRHL = 333-426,667spf, TS = 333-230,511 spf) reservoirs. Unmarked rainbow trout in both reservoirs had significantly higher myxospore counts than stocked fish of either strain. There were significant differences in M. cerebralis prevalence and myxospore loads among other naturally reproducing salmonids in the reservoirs. The trend in susceptibility was cutthroat trout Oncorhynchus clarkii > kokanee Oncorhynchus nerka > brown trout Salmo trutta. The GRHL performed well in both hatchery and field settings and is recommended for stocking programs.