Application and evaluation of a high-resolution mass spectrometry screening method for veterinary drug residues in incurred fish and imported aquaculture samples.

The ability to detect chemical contaminants, including veterinary drug residues in animal products such as fish, is an important example of food safety analysis. In this paper, a liquid chromatography high-resolution mass spectrometry (LC-HRMS) screening method using a quadrupole-Orbitrap instrument was applied to the analysis of veterinary drug residues in incurred tissues from aquacultured channel catfish, rainbow trout, and Atlantic salmon and imported aquacultured products including European eel, yellow croaker, and tilapia. Compared to traditional MS methods, the use of HRMS with nontargeted data acquisition and exact mass measurement capability greatly increased the scope of compounds that could be monitored simultaneously. The fish samples were prepared for analysis using a simple efficient procedure that consisted of an acidic acetonitrile extraction followed by solid phase extraction cleanup. Two different HRMS acquisition programs were used to analyze the fish extracts. This method detected and identified veterinary drugs including quinolones, fluoroquinolones, avermectins, dyes, and aminopenicillins at residue levels in fish that had been dosed with those compounds. A metabolite of amoxicillin, amoxicillin diketone, was also found at high levels in catfish, trout, and salmon. The method was also used to characterize drug residues in imported fish. In addition to confirming findings of fluoroquinolone and sulfonamide residues that were found by traditional targeted MS methods, several new compounds including 2-amino mebendazole in eel and ofloxacin in croaker were detected and identified. Graphical Abstract Aquacultured samples are analyzed with a high-resolution mass spectrometry screening method to detect and identify unusual veterinary drug residues including ofloxacin in an imported fish.

Microbiota of laboratory channel catfish skin mucosa and aquaria water exposed to chloramine-T trihydrate.

Here, we describe the skin mucosa microbiome of channel catfish (Ictalurus punctatus) before and after exposure to chloramine-T trihydrate. We also describe the aquaria water microbiome after the post-treatment period. These data provide a unique baseline description of skin mucosa and aquaria water microbiome from catfish reared in research aquaria.

Quality control ranges for testing broth microdilution susceptibility of Flavobacterium columnare and F. psychrophilum to nine antimicrobials.

A multi-laboratory broth microdilution method trial was performed to standardize the specialized test conditions required for the fish pathogens Flavobacterium columnare and F. psychrophilum. Nine laboratories tested the quality control (QC) strains Escherichia coli ATCC 25922 and Aeromonas salmonicida subsp. salmonicida ATCC 33658 against 10 antimicrobials (ampicillin, enrofloxacin, erythromycin, florfenicol, flumequine, gentamicin, ormetoprim/sulfadimethoxine, oxolinic acid, oxytetracycline, and trimethoprim/sulfamethoxazole) in diluted (4 g l-1) cation-adjusted Mueller-Hinton broth incubated at 28 and 18°C for 44-48 and 92-96 h, respectively. QC ranges were set for 9 of the 10 antimicrobials. Most of the minimal inhibitory concentration (MIC) distributions (16 of 18, 9 drugs at both temperatures) for A. salmonicida ATCC 33658 were centered on a single median MIC ± 1 two-fold drug dilution resulting in a QC range that spanned 3 dilutions. More of the E. coli ATCC 25922 MIC distributions (7 of 16) were centered between 2 MIC dilutions requiring a QC range that spanned 4 dilutions. A QC range could not be determined for E. coli ATCC 25922 against 2 antimicrobials at the low temperature. These data and their associated QC ranges have been approved by the Clinical and Laboratory Standards Institute (CLSI), and will be included in the next edition of the CLSI M49-A Guideline. This method represents the first standardized reference method for testing fish pathogenic Flavobacterium spp.

Phish-Pharm: A Searchable Database of Pharmacokinetics and Drug Residue Literature in Fish - 2022 Update.

A new version of Phish-Pharm: a Searchable Database of Pharmacokinetics and Drug Residue Literature in Fish has been updated and posted online at: http://www.fda.gov/AnimalVeterinary/ScienceResearch/ToolsResources/Phish-Pharm/default.htm . The new version contains over 700 articles encompassing 191 aquatic species (fish, shellfish, and more).Phish-Pharm, first released in 2005, accompanied an article in this Journal, titled "Fish Drug Analysis-Phish-Pharm: A Searchable Database of Pharmacokinetics Data in Fish," by R. Reimschuessel, L. Stewart, E. Squibb, K. Hirokawa, T. Brady, D. Brooks, B. Shaikh, C. Hodsdon, AAPS Journal. 2005;07(02):E288-E327, article 30. ( https://link.springer.com/article/10.1208/aapsj070230 )FDA understands that there are limited approved, conditionally approved, or indexed drugs available for use in aquatic animals. In response, FDA made this reference database publicly available to assist investigators in developing new animal drugs for aquatic species. The database also supports FDA Center for Veterinary Medicine's mission of protecting human and animal health by serving as a resource for the aquatic drug approval process and drug residue surveillance.Phish-Pharm is a Microsoft Access database that is periodically updated. Searchable fields include pharmacokinetic data and links to the abstract for each article. Phish-Pharm enables users to evaluate information on drugs and chemicals and to identify research gaps to guide future research. Phish-Pharm is not intended for aquaculture farmers to evaluate safety or effectiveness of unapproved drugs. Phish-Pharm is not an appropriate tool for recommending withdrawal intervals of drug and chemical residues due to variability among studies. Aquaculture farmers should only use approved, conditionally approved, or indexed drugs in their operations (see Approved Aquaculture Drugs ).

Epidemiological Cutoff Values for Standard Broth Microdilution Susceptibility Testing of Flavobacterium columnare Isolated from Fishes.

Flavobacterium columnare, the causative agent of columnaris disease in a large variety of freshwater fish, is a major problem in commercial aquaculture. A limited number of antimicrobial therapies are available to control this disease; therefore, these agents must be used judiciously. To facilitate effective monitoring for changes in susceptibility, the Clinical Laboratory Standards Institute (CLSI) has a standard broth microdilution test method specific for F. columnare. However, there are no CLSI-approved criteria (termed epidemiological cutoff values [ECVs]) to interpret results. Nevertheless, researchers have developed provisional ECVs based on testing by one laboratory. To satisfy CLSI data requirements, three laboratories used the standard method to generate additional antimicrobial susceptibility data against ampicillin, enrofloxacin, erythromycin, florfenicol, flumequine, gentamicin, oxolinic acid, oxytetracycline, sulfadimethoxine/ormetoprim, and sulfamethoxazole-trimethoprim using 109 F. columnare isolates. The new data combined with previously published data from 120 F. columnare isolates were analyzed and ECVs proposed to CLSI. Of the 10 antimicrobials, ECVs were approved for ampicillin, enrofloxacin, erythromycin, florfenicol, flumequine, oxolinic acid, and oxytetracycline, which were published in the 2020 edition of the CLSI document VET04 performance standards. These ECVs will help microbiologists categorize decreased antimicrobial susceptibility among F. columnare and will help in surveillance efforts to ensure judicious antimicrobial use.

Epidemiological Cutoff Values for Standard Broth Microdilution and Disk Diffusion Susceptibility Testing of Aeromonas hydrophila Isolated from Fish.

Aeromonas hydrophila and other closely related Aeromonas species cause motile aeromonad septicemia, a common fish disease. The disease affects many aquaculture sectors potentially requiring antimicrobial treatments. Therefore, researchers and laboratory diagnosticians need criteria called epidemiological cutoff values (ECVs) to determine whether a bacterial isolate has developed decreased susceptibility to an antimicrobial. To generate ECVs for this bacterium, we assembled a diverse collection of 245 isolates previously identified as A. hydrophila from fish. Using rpoD sequencing, we confirmed that 97 of the 245 isolates were A. hydrophila. We allocated the isolates among three laboratories and tested their susceptibility against eight antimicrobials using standard Clinical and Laboratory Standards Institute (CLSI) disk diffusion and broth microdilution methods. The resulting frequency distributions were statistically analyzed to determine wild-type cutoff estimates, which, along with scatterplots, were used to estimate potential ECVs. In collaboration with the CLSI, aquaculture working group, we proposed ECVs for six of the eight antimicrobials tested. Subsequently, the CLSI Subcommittee on Veterinary Antimicrobial Susceptibility Testing reviewed our data and approved the ECVs to be added to the 2020 edition of the VET04 performance standards for antimicrobial susceptibility testing of aquatic bacteria.

A No Observable Adverse Effects Level (NOAEL) for pigs fed melamine and cyanuric acid.

Ingesting melamine adulterated milk products led to kidney stones in many infants in 2008. This differs from the renal failure caused by intratubular crystal formation after co-ingestion of melamine (MEL) and cyanuric acid (CYA) in adulterated pet foods in 2007. To better understand the potential risk of developing crystal nephropathy following co-ingestion of MEL and CYA, we fed 16 weanling pigs 0, 1, 3.3, 10, 33, or 100 mg/kg bw/day of each MEL and CYA, or 200 mg/kg bw/day of either compound individually for 7 days. Crystals were found in the renal medulla and cortex and urine sediments of all pigs fed both MEL and CYA each at 10 mg/kg bw/day (or greater). Crystals were also found in one of the two pigs fed 200 mg/kg bw/day MEL-only. In a 28 day study, 36 weanling pigs were fed 0, 1, or 3.3 mg/kg bw/day of MEL and CYA or 200 mg/kg bw/day MEL-only. Only one of the 3.3 mg/kg MEL and CYA pig kidneys contained crystals. The no-observed-adverse-effect level (NOAEL) for pigs fed MEL and CYA for 28 days was concluded to be 1.0 mg/kg bw/day corresponding to 25 mg/kg (ppm) MEL and 25 mg/kg (ppm) CYA in dry feed.

In vitro effect of seven antiparasitics on Acolpenteron ureteroecetes (Dactylogyridae) from largemouth bass Micropterus salmoides (Centrarchidae).

Few drugs are approved by the United States Food and Drug Administration for treating parasite infections in minor species such as fish, due in part to the high cost of developing such drugs and to a relatively small market share for drug sponsors. Because in vivo effectiveness trials for antiparasitic drugs are costly, time consuming, and use many animals, a systematic in vitro screening approach to describe parasite motility could help find promising drug candidates. We evaluated the effects of 7 antiparasitics on the activity and survival of the endoparasitic monogenean Acolpenteron ureteroecetes (Dactylogyridae) collected from the posterior kidneys of juvenile largemouth bass Micropterus salmoides (Lacepede, 1802) (Centrarchidae) held in the laboratory. Tests were conducted in 12 well tissue culture plates; each well had 3 parasites, and we tested 3 concentrations and 1 control for each of the 7 antiparasitics. The parasites were observed immediately after adding the drug, at 1 to 3 h, and 17 to 26 h, and video recordings were made. Drug effects were recorded by documenting morbidity (reduced movement, tremors, contracted body, abnormal morphology) and mortality. A. ureteroecetes was strongly affected by the quinoline praziquantel, the imidazothiazide levamisole, and the organophosphates dichlorvos and trichlorfon. The parasites were moderately affected by the macrocyclic lactones ivermectin and emamectin, and generally unaffected by the benzimidazole mebendazole. Our study demonstrates the utility of characterizing in vitro responses with video microscopy to document responses of fish parasites for initial screens of drug effects on a fish monogenean.

Determination of tricaine residues in fish by liquid chromatography.

Tricaine methanesulfonate (MS-222) is approved by the U.S. Food and Drug Administration, Center for Veterinary Medicine (CVM), as an anesthetic drug for select aquaculture species. It was approved for use as a handling aid with a 3 week withdrawal time. The drug is rapidly metabolized and excreted; therefore, CVM approved its use without requiring a regulatory method for drug residues in tissues. However, there are concerns that the drug may be used to sedate fish during transport to slaughter. A regulatory method will enable monitoring for unsafe residues of this drug resulting from extralabel use. We present a quantitative method, using LC at a target level of 0.1 mg/kg (ppm), for three different farmed species: salmon (Salmo salar); tilapia (Oreochromis spp.); and catfish (Ictalurus punctatus). The assay begins with an acetonitrile extraction, followed by filtration and mixed-mode cation-exchange solid-phase extraction cleanup. The extracts are analyzed by reversed-phase LC with UV detection at 320 nm. The method was validated by using fish fillets with incurred residues, control fish fillets, and fish fillets fortified at half the target level, the target level, and twice the target level (0.05, 0.1, and 0.2 ppm, respectively). For all species, accuracy is > or =80% and the RSD is < or =10%. The method complies with CVM performance criteria for the determination of veterinary drug residues.

Evaluation of the renal effects of experimental feeding of melamine and cyanuric acid to fish and pigs.

OBJECTIVE: To determine whether renal crystals can be experimentally induced in animals fed melamine or the related triazine compound cyanuric acid, separately or in combination, and to compare experimentally induced crystals with those from a cat with triazine-related renal failure. ANIMALS: 75 fish (21 tilapia, 24 rainbow trout, 15 channel catfish, and 15 Atlantic salmon), 4 pigs, and 1 cat that was euthanatized because of renal failure. PROCEDURES: Fish and pigs were fed a target dosage of melamine (400 mg/kg), cyanuric acid (400 mg/kg), or melamine and cyanuric acid (400 mg of each compound/kg) daily for 3 days and were euthanatized 1, 3, 6, 10, or 14 days after administration ceased. Fresh, frozen, and formalin-fixed kidneys were examined for crystals. Edible tissues were collected for residue analysis. Crystals were examined for composition via Raman spectroscopy and hydrophilic-interaction liquid chromatography-tandem mass spectrometry. RESULTS: All animals fed the combination of melamine and cyanuric acid developed goldbrown renal crystals arranged in radial spheres (spherulites), similar to those detected in the cat. Spectral analyses of crystals from the cat, pigs, and fish were consistent with melamine-cyanurate complex crystals. Melamine and cyanuric acid residues were identified in edible tissues of fish. CONCLUSIONS AND CLINICAL RELEVANCE: Although melamine and cyanuric acid appeared to have low toxicity when administered separately, they induced extensive renal crystal formation when administered together. The subsequent renal failure may be similar to acute uric acid nephropathy in humans, in which crystal spherulites obstruct renal tubules.

Analysis of enterotoxigenic Bacillus cereus strains from dried foods using whole genome sequencing, multi-locus sequence analysis and toxin gene prevalence and distribution using endpoint PCR analysis.

Bacillus cereus strains were isolated from dried foods, which included international brands of spices from South East Asia, Mexico and India purchased from several retail stores, samples of powdered infant formula (PIF), medicated fish feed and dietary supplements. The genetic diversity of 64 strains from spices and PIF was determined using a multiplex endpoint PCR assay designed to identify hemolysin BL, nonhemolytic enterotoxin, cytotoxin K, and enterotoxin FM toxin genes. Thirteen different B. cereus toxigenic gene patterns or profiles were identified among the strains. Randomly selected B. cereus strains were sequenced and compared with reference Genomic Groups from National Center Biotechnology Information using bioinformatics tools. A comprehensive multi-loci sequence analysis (MLSA) was designed using alleles from 25 known MLST genes specifically tailored for use with whole genome assemblies. A cohort of representative genomes of strains from a few FDA regulated commodities like dry foods and medicated fish feed was used to demonstrate the utility of the 25-MLSA approach for rapid clustering and identification of Genome Groups. The analysis clustered the strains from medicated fish feed, dry foods, and dietary supplements into phylogenetically-related groups. 25-MLSA also pointed to a greater diversity of B. cereus strains from foods and feed than previously recognized. Our integrated approach of toxin gene PCR, and to our knowledge, whole genome sequencing (WGS) based sequence analysis, may be the first of its kind that demonstrates enterotoxigenic potential and genomic diversity in parallel.

Development of Similar Broth Microdilution Methods to Determine the Antimicrobial Susceptibility of Flavobacterium columnare and F. psychrophilum.

Flavobacterium columnare and F. psychrophilum are major fish pathogens that cause diseases that may require antimicrobial therapy. Choice of appropriate treatment is dependent upon determining the antimicrobial susceptibility of isolates. Therefore we optimized methods for broth microdilution testing of F. columnare and F. psychrophilum to facilitate standardizing an antimicrobial susceptibility test. We developed adaptations to make reproducible broth inoculums and confirmed the proper incubation time and media composition. We tested the stability of potential quality-control bacteria and compared test results between different operators. Log phase occurred at 48 h for F. columnare and 72-96 h for F. psychrophilum, confirming the test should be incubated at 28°C for approximately 48 h and at 18°C for approximately 96 h, respectively. The most consistent susceptibility results were achieved with plain, 4-g/L, dilute Mueller-Hinton broth supplemented with dilute calcium and magnesium. Supplementing the broth with horse serum did not improve growth. The quality-control strains, Escherichia coli ATCC 25922 and Aeromonas salmonicida subsp. salmonicida ATCC 33658, yielded stable minimal inhibitory concentrations (MIC) against all seven antimicrobials tested after 30 passes at 28°C and 15 passes at 18°C. In comparison tests, most MICs of the isolates agreed 100% within one drug dilution for ampicillin, florfenicol, and oxytetracycline. The agreement was lower with the ormetoprim-sulfdimethoxine combination, but there was at least 75% agreement for all but one isolate. These experiments have provided methods to help standardize antimicrobial susceptibility testing of these nutritionally fastidious aquatic bacteria. Received June 24, 2015; accepted October 2, 2015.

Marker residue determination of tritium-labeled ivermectin in the muscle of aquacultured largemouth bass, hybrid striped bass, and yellow perch following oral treatment.

The residue depletion profiles of tritium-labeled ivermectin and its metabolites in the muscle of aquacultured largemouth bass (LMB), hybrid striped bass (HSB), and yellow perch (YP) following oral treatment are reported. Fish were administered ³H-ivermectin at the dose level of 0.1 mg/kg body weight (7-9 µCi) in a gel capsule via stomach tube. At each postdose withdrawal time, six fish of each species were sedated with buffered MS-222 and blood samples taken. Fish were then euthanized, and fillets with adhering skin (scales removed) and bile samples were collected. The muscle fillets were homogenized in dry ice to a fine powder. Aliquots of tissue, plasma, and bile were assayed for total radioactive residue (TRR). The homogenized muscle was extracted in acetonitrile or methanol followed by high-performance liquid chromatographic (HPLC) analysis to determine the presence of parent ivermectin and its potential metabolites. The highest TRR concentrations (ivermectin equivalents) of 53, 45, and 44 ng/g (ppb) were obtained on postdose day 1 for HSB, LMB, and YP, respectively. The TRR depleted most slowly in HSB to 25 ppb at day 91, followed by YP to 19 ppb at day 42 and then by LMB to 22 ppb at day 35. The total residue of ivermectin and its metabolites by HPLC analysis followed the same depletion pattern in the three species. Additionally, the depletion rate of TRR of ³H-ivermectin in the three species followed the pattern bile > plasma > muscle. The results further indicate that one of the polar metabolites of ivermectin could serve as a potential marker residue as an indication of use, rather than the parent ivermectin.

Depletion of melamine and cyanuric acid in serum from catfish Ictalurus punctatus and rainbow trout Onchorhynchus mykiss.

Melamine and its triazine analogs, such as cyanuric acid, have been used to artificially inflate protein content both in animal feed ingredients, as well as in milk products produced for human consumption. We report here a LC-MS/MS method to quantify and confirm melamine and cyanuric acid in serum from channel catfish and rainbow trout with a limit of quantification of 0.8 µg/mL. The method was applied to serum samples from a residue depletion study in which fish were given a single oral dose of 20 mg/kg body weight melamine, cyanuric acid, or both compounds together. Samples were taken at 1, 3, 7, 14, and 28 days (an additional 42 day was added for trout). When given alone or in combination with cyanuric acid, melamine residues were highest on day 1 in both catfish and trout. Cyanuric acid was only quantifiable at day 1 in trout when given alone, and not at all in catfish. The serum half life of melamine in catfish was 1.50-1.62 days and 3.09-3.67 days in trout. This work highlights the differences of depletion kinetics in fish, which can be measured in days, as compared to the depletion in mammals, measured in hours.

Bioaccumulation of melamine in catfish muscle following continuous, low-dose, oral administration.

In this study, catfish muscle was analyzed for melamine (MEL) and cyanuric acid (CYA) residues following experimental feeding with low doses of MEL and MEL and CYA (MEL+CYA) and with the insoluble melamine-cyanurate complex (MEL=CYA). Catfish were daily fed 0.1 mg/kg BW of MEL for 15, 28, or 42 days, 0.1 mg/kg BW of MEL+CYA for 28 days, 2.5 mg/kg BW of MEL+CYA for 14 days, or 400 mg/kg BW of MEL=CYA for 3 days. Residues in the tissue were determined by LC-MS/MS. MEL was extracted with acidic acetonitrile, followed by defatting with dichloromethane, and isolated with cation exchange solid phase extraction (SPE). For CYA analysis, fish were extracted with dilute acetic acid, defatted with hexane, and cleaned up with a graphitic carbon SPE. Catfish fed 0.1 mg/kg BW of MEL reached a maximum muscle residue concentration of 0.33 ± 0.04 mg/kg (ppm) after 28 days of continuous feeding. The same concentration was found for MEL+CYA feeding at the 0.1 mg/kg BW level for 28 days. Feeding at 2.5 mg/kg BW of MEL+CYA yielded muscle concentrations above the 2.5 mg/kg level of concern for most of the study fish. Finally, catfish fed high levels of the MEL=CYA complex (400 mg/kg BW) accumulated relatively little MEL in the muscle (0.14 ± 0.07 mg/kg) and, unlike treatment with MEL+CYA, did not form renal melamine-cyanurate crystals. Appreciable concentrations of CYA were not detected in any of the muscles tested. These studies provide data to model the bioaccumulation of triazine residues into edible fish tissue as a result of the continuous consumption of adulterated feed.

Residue depletion of albendazole and its metabolites in the muscle tissue of large mouth and hybrid striped bass after oral administration.

The residue depletion profiles of albendazole (ABZ) and its major metabolites: albendazole sulfoxide (ABZ-SO), albendazole sulfone (ABZ-SO(2)) and albendazole aminosulfone (ABZ-2-NH(2)SO(2)) were studied in the muscle tissues of large mouth (LMB) and hybrid striped bass (HSB). A single oral dose of 10mg/kg albendazole was given to the two fish species via intra-gastric tube. The muscle tissues with adhering skin were collected at 8, 16, 24, 48, 72, 96 and 120h post dose from both species. The samples were homogenized in dry ice and subjected to extraction and cleanup procedures. The final sample extracts were analyzed by high performance liquid chromatography. The results indicate that both ABZ and its pharmacologically active metabolite ABZ-SO were retained longer in LMB than in HSB after oral treatment. Albendazole was detectable until 8h or 6.7 degree days ( degrees D) and 48h (40 degrees D) in HSB and LMB, respectively. However, ABZ-SO was detectable up to 48h (40 degrees D) and 96h (80 degrees D) in HSB and LMB, respectively. Among the inactive metabolites, ABZ-SO(2) was present in both fish species; however, ABZ-2-NH(2)SO(2) was detected only in LMB.

Simultaneous screening and confirmation of multiple classes of drug residues in fish by liquid chromatography-ion trap mass spectrometry.

LC-ion trap mass spectrometry was used to screen and confirm 38 compounds from a variety of drug classes in four species of fish: trout, salmon, catfish, and tilapia. Samples were extracted with acetonitrile and hexane. The acetonitrile phase was evaporated, redissolved in water and acetonitrile, and analyzed by gradient chromatography on a phenyl column. MS(2) or MS(3) spectra were monitored for each compound. Qualitative method performance was evaluated by the analysis over several days of replicate samples of control fish, fish fortified with a drug mixture at 1 ppm, 0.1 ppm and 0.01 ppm, and fish dosed with a representative from each drug class. Half of the 38 drugs were confirmed at 0.01 ppm, the lowest fortification level. This included all of the quinolones and fluoroquinolones, the macrolides, malachite green, and most of the imidazoles. Florfenicol amine, metronidazole, sulfonamides, tetracyclines, and most of the betalactams were confirmed at 0.1 ppm. Ivermectin and penicillin G were only detectable in the 1 ppm fortified samples. With the exception of amoxicillin, emamectin, metronidazole, and tylosin, residue presence was confirmed in all the dosed fish.

Determination of cyanuric acid residues in catfish, trout, tilapia, salmon and shrimp by liquid chromatography-tandem mass spectrometry.

In May 2007, investigators discovered that waste material from the pet food manufacturing process contaminated with melamine (MEL) and/or cyanuric acid (CYA) had been added to hog and chicken feeds. At this time, investigators also learned that adulterated wheat gluten had been used in the manufacture of aquaculture feeds. Concern that the contaminated feed had been used in aquaculture and could enter the human food supply prompted the development of a method for the determination of CYA residues in the edible tissues of fish and shrimp. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was employed as a sensitive technique for the analysis of CYA in catfish, tilapia, salmon, trout and shrimp tissue. CYA was extracted from ground fish or shrimp with an acetic acid solution, defatted with hexane, and isolated with a graphitic carbon black solid-phase extraction column. Residues were separated from matrix components using a porous graphitic carbon LC column, and then analyzed with electrospray ionization in negative ion mode on a triple quadrupole mass spectrometer. Selective reaction monitoring was performed on the [M-H](-)m/z 128 ion resulting in the product ions m/z 85 and 42. Recoveries from catfish, tilapia and trout fortified with 10-100 microgkg(-1) of CYA averaged 67% with a relative standard deviation (R.S.D.) of 18% (n=107). The average method detection limit (MDL) for catfish, tilapia and trout is 3.5 microgkg(-1). An internal standard, (13)C(3)-labeled CYA, was used in the salmon and shrimp extractions. Average recovery of CYA from salmon was 91% (R.S.D.=15%, n=18) with an MDL of 7.4 microgkg(-1). Average recovery of CYA from shrimp was 85% (R.S.D.=10%, n=13) with an MDL of 3.5 microgkg(-1).

Determination and confirmation of melamine residues in catfish, trout, tilapia, salmon, and shrimp by liquid chromatography with tandem mass spectrometry.

Pet and food animal (hogs, chicken, and fish) feeds were recently found to be contaminated with melamine (MEL). A quantitative and confirmatory method is presented to determine MEL residues in edible tissues from fish fed this contaminant. Edible tissues were extracted with acidic acetonitrile, defatted with dichloromethane, and cleaned up using mixed-mode cation exchange solid-phase extraction cartridges. Extracts were analyzed by liquid chromatography with tandem mass spectrometry with hydrophilic interaction chromatography and electrospray ionization in positive ion mode. Fish and shrimp tissues were fortified with 10-500 microg/kg (ppb) of MEL with an average recovery of 63.8% (21.5% relative standard deviation, n = 121). Incurred fish tissues were generated by feeding fish up to 400 mg/kg of MEL or a combination of MEL and the related triazine cyanuric acid (CYA). MEL and CYA are known to form an insoluble complex in the kidneys, which may lead to renal failure. Fifty-five treated catfish, trout, tilapia, and salmon were analyzed after withdrawal times of 1-14 days. MEL residues were found in edible tissues from all of the fish with concentrations ranging from 0.011 to 210 mg/kg (ppm). Incurred shrimp and a survey of market seafood products were also analyzed as part of this study.

Laboratory transmission of the monogenean Acolpenteron ureteroecetes infecting the posterior kidneys of largemouth bass: time course and pathology.

Acolpenteron ureteroecetes infections in the kidneys of largemouth bass Micropterus salmoides have been reported, but the time course of infection and progression of pathology in experimentally infected fish remain unknown. We exposed 299 naive juvenile largemouth bass at 19.8 degrees C to A. ureteroecetes-infected largemouth bass via recirculating water without direct contact. For 7 months, prevalence and density were determined monthly in squashes of posterior kidney (20 exposed fish, 20 nonexposed fish), and histopathology was assessed in 5 fish from each group. Prevalence increased steadily from months 1 (5%) to 4 (85%), thereafter remaining relatively stable. Mean density of infection doubled monthly (month 1, 0.1 individuals/2 cm2 squash; month 7, 15.1 individuals/2 cm2 squash). Eggs were first observed at month 3, and mean density increased markedly from month 4 to month 5 (2.9-15.3 eggs/2 cm2 squash). Histopathology showed damage in renal collecting ducts that got progressively worse between 5 and 7 months. The infected ducts were dilated, had a hyperplastic epithelium, and were surrounded by chronic inflammation, including eosinophilic granular cells and varying degrees of fibrosis. Eggs within granulomas were present in the interstitium; this response is newly reported. The infection system developed in this study provides a reproducible and consistent source of infected individuals that will facilitate further study of the parasite and potential treatments.