Colleen A. Caldwell

Distribution of Tubifex tubifex Lineages and Myxobolus cerebralis Infection in the Tailwater of the San Juan River, New Mexico

Abstract We chose a hypolimnetic-release tailwater of the San Juan River, New Mexico, to characterize the etiology of whirling disease, a parasitic infection of salmonids. We sampled a 2-km reach of the tailwater in August and December 2001 and June 2002 to characterize environmental factors influencing the distribution and density of Tubifex tubifex lineages and Myxobolus cerebralis infection rates. Shortly after the scouring flow, organic matter in sediments and T. tubifex densities increased within deep habitats. In contrast, no differences were observed in T. tubifex densities and organic matter collected from shallow habitats throughout the three sampling dates. Within this study area, we found three sympatric lineages of T. tubifex (lineages I, III, and VI). Lineage VI dominated riffle reaches, whereas lineages I, III, and VI were observed in pool habitats. Myxobolus cerebralis infection rates were higher in T. tubifex collected in pool habitats (3.01%) than in those collected in riffle habitats (0....

INHIBITION OF ERYTHROCYTE δ-AMINOLEVULINIC ACID DEHYDRATASE (ALAD) ACTIVITY IN FISH FROM WATERS AFFECTED BY LEAD SMELTERS

We assessed the effects on fish of lead (Pb) released to streamsby smelters located in Trail, BC (Canada), E. Helena, MT, Herculaneum, MO, and Glover, MO. Fish were collected by electrofishing from sites located downstream of smelters and from reference sites. Blood from each fish was analyzed for δ-aminolevulinic acid dehydratase (ALAD) activity and hemoglobin (Hb), and samples of blood, liver, or carcass were analyzed for Pb, zinc (Zn), or both. Fish collected downstreamof all four smelters sites had elevated Pb concentrations, decreased ALAD activity, or both relative to their respectivereference sites. At E. Helena, fish from the downstream site also had lower Hb concentrations than fish from upstream. Differences among taxa were also apparent. Consistent with previous studies, ALAD activity in catostomids (Pisces: Catostomidae-northern hog sucker, Hypentelium nigricans;river carpsucker, Carpiodes carpio; largescale sucker, Catostomus macrocheilus; and mountain sucker, C. platyrhynchus) seemed more sensitive to Pb-induced ALAD inhibition than the salmonids (Pisces: Salmonidae-rainbow trout,Oncorhynchus mykiss; brook trout, Salvelinus fontinalis) or common carp (Cyprinus carpio). Some of these differences may have resulted from differential accumulation of Zn, which was not measured at all sites. We detected no ALAD activity in channel catfish (Ictaluruspunctatus) from either site on the Mississippi River at Herculaneum, MO. Our findings confirmed that Pb is releasedto aquatic ecosystems by smelters and accumulated by fish, andwe documented potentially adverse effects of Pb in fish. We recommend that Zn be measured along with Pb when ALAD activityis used as a biomarker and the collection of at least 10 fish ofa species at each site to facilitate statistical analysis.

Effects of Temperature, Photoperiod, and Myxobolus cerebralis Infection on Growth, Reproduction, and Survival of Tubifex tubifex Lineages

Abstract Tubifex tubifex is the definitive host for Myxobolus cerebralis, the causative agent of whirling disease in salmonid fish. Several mitochondrial lineages of T. tubifex exhibit resistance to M. cerebralis infection. Release of the triactinomyxon form of the parasite from T. tubifex varies with water temperature; however, little is known about the interactive effects of temperature and photoperiod on the susceptibility of T. tubifex lineages to M. cerebralis infection. In addition, the environmental effects on the growth, reproduction, and survival of T. tubifex lineages are unknown. Monocultures of lineages III and VI were subjected to infection (0 and 500 myxospores per worm), a range of temperatures (5, 17, and 27°C), and various diurnal photoperiods (12:12, 14:10, and 16:8 dark: light) over a 70-d period by using a split–split plot experimental design. Lineage VI resisted infection by M. cerebralis at all temperatures, whereas lineage III exhibited infection levels of 4.3% at 5°C, 3.3% at 17°C,...

Analysis of Regional Scale Risk of Whirling Disease in Populations of Colorado and Rio Grande Cutthroat Trout Using a Bayesian Belief Network Model

Introduction and spread of the parasite Myxobolus cerebralis, the causative agent of whirling disease, has contributed to the collapse of wild trout populations throughout the intermountain west. Of concern is the risk the disease may have on conservation and recovery of native cutthroat trout. We employed a Bayesian belief network to assess probability of whirling disease in Colorado River and Rio Grande cutthroat trout (Oncorhynchus clarkii pleuriticus and Oncorhynchus clarkii virginalis, respectively) within their current ranges in the southwest United States. Available habitat (as defined by gradient and elevation) for intermediate oligochaete worm host, Tubifex tubifex, exerted the greatest influence on the likelihood of infection, yet prevalence of stream barriers also affected the risk outcome. Management areas that had the highest likelihood of infected Colorado River cutthroat trout were in the eastern portion of their range, although the probability of infection was highest for populations in the southern, San Juan subbasin. Rio Grande cutthroat trout had a relatively low likelihood of infection, with populations in the southernmost Pecos management area predicted to be at greatest risk. The Bayesian risk assessment model predicted the likelihood of whirling disease infection from its principal transmission vector, fish movement, and suggested that barriers may be effective in reducing risk of exposure to native trout populations. Data gaps, especially with regard to location of spawning, highlighted the importance in developing monitoring plans that support future risk assessments and adaptive management for subspecies of cutthroat trout.

Effects of Depleted Uranium on Survival, Growth, and Metamorphosis in the African Clawed Frog (Xenopus laevis)

Embryos (stage 8–47, Nieuwkoop and Faber) of the African clawed frog (Xenopus laevis) were subjected to water-borne depleted uranium (DU) concentrations that ranged from 4.8 to 77.7 mg/L using an acute 96-h frog embryo teratogenesis assay–Xenopus (FETAX). In a chronic 64-d assay, X. laevis (from embryo through metamorphosis; stages 8–66) were subjected to concentrations of DU that ranged from 6.2 to 54.3 mg/L. Our results indicate DU is a non teratogenic metal. No effects on mortality, malformations, or growth were observed in the 96-h FETAX with concentrations of DU that ranged from 4.8 to 77.7 mg/L. From stage 8 to stage 47, X. laevis tadpoles do not actively feed and the gills are not well developed. Thus, uptake of DU was reduced despite exposure to elevated concentrations. The 64-d assay resulted in no concentration response for either mortality or malformations; however, a delay in metamorphosis was observed in tadpoles subjected to elevated DU concentrations (from 13.1 to 54.3 mg/L) compared to tadpoles in both the well-water control and reference. The delay in metamorphosis was likely due to increasing body burden of DU that ranged from 0.98 to 2.82 mg/kg.

Observations of Health Indices Used to Monitor a Tailwater Trout Fishery

Abstract Health of the population of rainbow trout Oncorhynchus mykiss in the San Juan River tailwater was monitored to determine the effects of potential crowding from a reduced winter flow test at Navajo Dam, northwestern New Mexico. A systematic necropsy-based health profile provided a rapid method to detect gross changes in the health of the fish population. The health assessment index (HAI) was calculated to quantify the necropsy system and allow statistical comparisons of data sets. Other suborganismic indices were selected to encompass a range of responses specific to the stress of environmental alterations: physiology assessment using total protein and percent muscle lipids, an immune assessment using serum lysozyme, and a cellular-based evaluation using histology. The HAI values showed no clear trend in fish health, although significant differences occurred among fish samples during the test. Significant declines in condition factors and percent muscle lipids throughout the study suggested a seas...

Diet Optimization of Juvenile Rio Grande Silvery Minnow

Abstract Captive propagation of the federally endangered Rio Grande silvery minnow Hybognathus amarus has been identified as essential for the recovery of the species. A starter diet was initially developed for this cyprinid to support rapid growth through the larval stage. The diet, however, was too costly to support the grower phase of the species. A series of trials was conducted to determine whether a grower diet could be developed that would be cost effective while maintaining fish performance. Quadruplicate lots of Rio Grande silvery minnow (approximately 90 d posthatch, 0.39–0.42 g) were fed a reference diet or one of five experimental diets until just before gonadal maturation at two facilities in New Mexico (New Mexico State University [NMSU] and Dexter National Fish Hatchery and Technology Center [Dexter]). The diets varied in percent composition of ingredients to account for a range in feed costs. Cyclop-eeze (Argent, Redmond, Washington), krill, liver, and fish meals were present in the refere...

Upper Thermal Tolerances of Rio Grande Cutthroat Trout under Constant and Fluctuating Temperatures

Abstract The Rio Grande Cutthroat Trout Oncorhynchus clarkii virginalis is the southernmost subspecies of Cutthroat Trout, and as with the other subspecies, stream temperature regulates growth, reproductive success, distribution, and survival. An understanding of the upper thermal tolerance of Rio Grande Cutthroat Trout is important for developing water temperature standards and for assessing suitable habitat for reintroduction and management. Hatch success of Rio Grande Cutthroat Trout eggs was determined under static temperatures. The thermal requirements of fry and juveniles were also assessed under static and fluctuating temperature regimes using the acclimated chronic exposure method. Egg hatch success was 46–70% from 6°C to 16°C but declined significantly at 18°C and 20°C. Maximum growth of fry that were fed to satiation occurred at 15.3°C. The 30-d ultimate upper incipient lethal temperature (UUILT) was 22.6°C for fry and 21.7°C for juveniles. Survival during fluctuating temperature experiments was...

Relative Susceptibility and Effects on Performance of Rio Grande Cutthroat Trout and Rainbow Trout Challenged with Myxobolus cerebralis

Abstract We evaluated the susceptibility of Rio Grande cutthroat trout (RGCT) Oncorhynchus clarkii virginalis to infection by Myxobolus cerebralis in a laboratory experiment. In the same experiment, rainbow trout (RBT) O. mykiss were similarly exposed to M. cerebralis as a reference of known sensitivity to the parasite. Treatments consisting of six parasite concentrations (0, 50, 100, 250, 500, and 1,000 triactinomyxons [TAMS] per fish) were randomized within a complete block design using RGCT and RBT fry beginning at 60 d posthatch (600 degree-days at 10°C). The laboratory experiment was terminated at 130 d postexposure (1,900 degree-days at 10°C). Diagnostic metrics included clinical signs (behavioral and black tail), survival, myxospore counts, histology, and a swimming performance challenge. Clinical signs of whirling disease were observed within both species at 500 and 1,000 TAMs/fish by 66 d postexposure to the disease. Rio Grande cutthroat trout exhibited significantly lower survival (50% cumulativ...

Physiological Stress Responses of Rio Grande Silvery Minnow: Effects of Individual and Multiple Physical Stressors of Handling, Confinement, and Transport

Abstract In an attempt to reestablish populations of Rio Grande silvery minnow Hybognathus amarus within its former range, initiatives were set forth to propagate the species in hatcheries, augment wild populations through repatriation, and rescue the species from isolated and receding pools. Physical stressors associated with these recovery efforts, however, result in stress that increases the vulnerability of the minnow to opportunistic pathogens and predation, possibly decreasing poststocking survival. We assessed the physiological stress response to standard management practices by characterizing the changes in plasma cortisol, glucose, and osmolality. When subjected to the individual stressors of 30 s of handling, 3 h of confinement (density, 100 kg/m3), or 3 h of transport (density, 40 kg/m3), moderate changes in plasma glucose and plasma osmolality were observed during recovery whereas changes in plasma cortisol were not detectable. When fish were subjected to consecutive stressors (30 s of handlin...