Geology topics

Guy R. Stehly

Publications and source records attributed to Guy R. Stehly.

7 recordsLinked to original sources

USGS2003

Residue depletion of oxytetracycline from fillet tissues of northern pike and walleye

The broad-spectrum antibacterial drug oxytetracycline (OTC) is used in the U.S. to treat certain diseases in salmonids and catfish. This study was conducted to support an extension of the OTC label to include all cool-water fish species cultured at U.S. public aquaculture facilities by satisfying human food safety requirements. Juvenile northern pike ( Esox lucius ; mean weight: 117 g) and walleye ( Stizostedion vitreum ; mean weight: 59 g) were fed OTC-medicated diets near the maximum legal treatment rate (82.7 mg OTC-HCl/kg fish/day for 10 days) and near the lower limit of the water temperature range for most disease outbreaks in these species (14 and 16 °C, respectively). Two trials were conducted simultaneously with northern pike, one using commercially medicated feed and the other using on-site OTC top-coated feed. A third trial was performed with walleye using on-site OTC top-coated feed. Fillet tissues were collected and OTC free base (OTC-base) concentrations were determined by high performance liquid chromatography. The maximum mean OTC-base concentrations in the fillet tissue were 319 ng/g in northern pike (skinless) and 721 ng/g in walleye (skin-on), both well below the current tolerance limit of 2000 ng/g OTC-base. The log-linear loss of OTC-base from the fillet tissues was monophasic, with terminal phase half-lives of 5.9 days in northern pike fed commercial medicated feed, 6.7 days in northern pike fed top-coated feed, and 10.5 days in walleye fed top-coated feed. The data supported a zero withdrawal time in juvenile northern pike and walleye fed OTC at the approved dose level for 10 days at water temperatures down to 14 and 16 °C respectively.

Aquaculture↗

USGS2002

Liquid chromatographic determination of florfenicol in the plasma of multiple species of fish

A simple method was developed for determining florfenicol concentration in a small volume (250 μl) of plasma from five phylogenetically diverse species of freshwater fish. Florfenicol was isolated from the plasma matrix through C 18 solid-phase extraction and quantified by reversed-phase high-performance liquid chromatography with UV detection. The accuracy (84–104%), precision (%RSD⩽8), and sensitivity (quantitation limit <30 ng/ml) of the method indicate its usefulness for conducting pharmacokinetic studies on a variety of freshwater fish.

Journal of Chromatography B: Analytical Technologi↗

USGS2001

Oxytetracycline depletion from skin-on fillet tissue of coho salmon fed oxytetracycline medicated feed in freshwater at temperatures less than 9°C

Oxytetracycline (OTC) is a broad spectrum antibacterial agent approved in the USA for treating certain bacterial diseases in salmonids cultured in freshwater at temperatures greater than or equal to 9°C. This study was conducted to provide the information necessary to expand the OTC label to include treatment of diseased salmonids cultured in freshwater at temperatures below 9°C. The study was designed to treat juvenile coho salmon ( Oncorhynchus kisutch ) with OTC-medicated feed and determine the depletion of OTC from the skin-on fillet tissue. Oxytetracycline depletion was evaluated in juvenile coho salmon (weight range, 13–62 g) fed OTC-medicated feed at a rate of 88.2 mg OTC/kg body weight/day for 10 days. Pairs of skin-on fillets were taken from individual fish on days 4 and 10 during the treatment phase and on days 1, 4, 8, 14, and 19 during the depletion phase. Water temperatures during the study period ranged from 4.1°C to 8.5°C. The OTC concentrations in medicated feed and skin-on fillets were determined with high-performance liquid chromatography methods. The maximum mean OTC concentration in fillet tissue was 932 ng/g, 1 day after the last treatment and decreased to 32 ng/g 19 days after the last treatment. The log-linear loss of OTC from the fillet tissue was biphasic with a terminal phase half-life of 4.9 days.

Aquaculture↗

USGS1998

Experimental infection of rainbow trout with Saprolegnia parasitica

A method was developed to experimentally induce saprolegniasis in rainbow trout Oncorhynchus mykiss. The development of a reliable method to produce infected fish is essential to efforts to determine the efficacy of various antifungal treatments. Three methods for inducing saprolegniasis were evaluated in waters containing known concentrations of Saprolegnia parasitica zoospores. These methods included application of the following stressors to fish: (1) abrasion and dewatering, (2) water temperature increase, and (3) a combination of abrasion, dewatering, and temperature increase. Neither physical abrasion nor temperature increase stress alone was effective for inducing saprolegniasis. Only 25.9% of fish stressed by abrasion and dewatering alone became infected. Application of both abrasion and temperature stress, however, induced saprolegniasis in 77.8% of fish tested. Most of these fish became infected after 5 d of stress treatments. No fish became infected or died in the positive control group (not stressed but exposed to S. parasitica zoospores) or the negative control group (not stressed or challenged). This method should enable researchers to induce saprolegniasis in rainbow trout to study its pathogenesis or to test the efficacy of antifungal treatments. In conducting efficacy studies, it is important that therapeutic treatments begin promptly after the first signs of saprolegniasis are observed because the disease can progress very quickly and often results in mortality.

Journal of Aquatic Animal Health↗

USGS1993

Pharmacokinetics, tissue distribution, and metabolism of nitrofurantoin in the channel catfish (Ictalurus punctatus)

The pharmacokinetics, tissue distribution, and metabolism of the drug nitrofurantoin were examined in the channel catfish ( Ictalurus punctatus ) after intravascular or oral dosing. Mean plasma concentrations of nitrofurantoin after intravascular administration at 1 and 10 mg kg −1 of body weight were best fit to two- and three-compartment pharmacokinetic models, respectively. Nitrofurantoin was rapidly eliminated from the plasma after intravascular dosing; at 1 and 10 mg kg −1 , the terminal half-lives were 23 and 46 min, respectively. After oral dosing at 1 mg kg −1 , peak plasma concentrations (0.06 μg ml −1 ) occurred at 2 h; the bioavailability was 17%. Residues of nitrofurantoin and its metabolites in the tissues were initially eliminated rapidly but persisted at the later sampling times. Residue concentrations were highest in the plasma and excretory tissues. Approximately 21% and 4% of the oral dose were eliminated in the urine and bile, respectively. Parent nitrofurantoin was the major radiolabelled compound found in the urine; however, the percentage of total residues composed of metabolites increased with time. Biliary residues consisted mostly of nitrofurantoin metabolites. High-performance liquid chromatography revealed the presence of at least five metabolites in the urine and bile.

Aquaculture↗

USGS1990

Toxicokinetics of PAHs in Hexagenia

The accumulation kinetics of two waterborne polycyclic aromatic hydrocarbons (PAHs), benzo[a]pyrene (BAP) and phenanthrene (PHE), were studied in the mayfly nymph ( Hexagenia limbata ). The uptake clearance decreased while the bioconcentration of BAP increased with an increase in weight of the H. limbata nymph. The relationship between uptake clearance and bioconcentration for PHE was variable, and bioconcentration was greater for the heavier animals. Two kinetic models were used to evaluate the effect of nymph weight on disposition of PAHs: (a) the amount-uptake clearance model, similar to models most frequently used in environmental toxicology; and (b) a clearance-volume model, similar to models used in clinical pharmacology. The two models gave similar predictive results but were different in a few cases. These differences in common parameter estimation probably resulted from methodologies used and high data variability rather than the models themselves, since they are mathematically equal. Some of the parameters are unique to each of the models and are defined and described. The clearance of oxygen from water is inversely and linearly related to the weight of the mayfly nymphs, but oxygen clearances were always much less than the uptake clearances of the PAHs. The high PAH uptake clearance compared to oxygen clearance implies a greater surface area or efficiency for PAH accumulation from water.

Environmental Toxicology and Chemistry↗

USGS1990

Pharmacokinetic modeling in aquatic animals. 1. Models and concepts

While clinical and toxicological applications of pharmacokinetics have continued to evolve both conceptually and experimentally, pharmacokinetics modeling in aquatic animals has not progressed accordingly. In this paper we present methods and concepts of pharmacokinetic modeling in aquatic animals using multicompartmental, clearance-based, non-compartmental and physiologically-based pharmacokinetic models. These models should be considered as alternatives to traditional approaches, which assume that the animal acts as a single homogeneous compartment based on apparent monoexponential elimination.

Aquatic Toxicology↗