U.S. Department of Agriculture (USDA) 

Food Safety and Inspection Service (FSIS) 

Data Summary of Siluriformes Fish Testing: 

A Five-Year Review, FY 2016-2020 

March 29, 2022 

Tracy Berutti 

Randolph Duverna 

Gurinder Saini 

Wayne Schlosser 

Erika Stapp-Kamotani 
Siluriformes fish data summary 29 March 2022 

Contents 

Executive Summary................................................................................................................................................. 4 

Introduction ........................................................................................................................................................ 4 

Purpose ............................................................................................................................................................... 4 

Overall Findings................................................................................................................................................... 4 

Recommendations .............................................................................................................................................. 5 

Background ............................................................................................................................................................. 6 

History ................................................................................................................................................................. 6 

2015 Risk Assessment ......................................................................................................................................... 6 

Salmonella....................................................................................................................................................... 6 

Salmonella Illness Estimates from 2015 Risk Assessment .............................................................................. 7 

Current Inspection/Testing Program Features ....................................................................................................... 7 

Domestic ............................................................................................................................................................. 7 

Import.................................................................................................................................................................. 7 

Domestic vs Import Volume................................................................................................................................ 7 

Methods/Approach................................................................................................................................................. 8 

Microbiological Testing ....................................................................................................................................... 8 

Chemical Residue Testing.................................................................................................................................... 8 

Literature Review ................................................................................................................................................ 8 

Contaminants in the Environment.................................................................................................................. 8 

Aquaculture..................................................................................................................................................... 9 

Salmonella in Siluriformes Fish Production .................................................................................................... 9 

Outbreak Data................................................................................................................................................. 9 

Data ....................................................................................................................................................................... 10 

Results ................................................................................................................................................................... 10 

General Testing Results..................................................................................................................................... 10 

Chemical Residues............................................................................................................................................. 11 

Dyes............................................................................................................................................................... 11 

Multi-Residue Method (MRM)...................................................................................................................... 12 

Nitrofurans .................................................................................................................................................... 13 

Pesticides ...................................................................................................................................................... 14 

Metals ........................................................................................................................................................... 17 

Arsenic....................................................................................................................................................... 19 

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Siluriformes fish data summary 29 March 2022 

Strontium .................................................................................................................................................. 20 

Lead ........................................................................................................................................................... 20 

Nickel......................................................................................................................................................... 21 

Cadmium ................................................................................................................................................... 21 

Chromium.................................................................................................................................................. 22 

Salmonella..................................................................................................................................................... 22 

Risk Characterization for Salmonella ........................................................................................................ 24 

Salmonella Sampling for Siluriformes Fish Compared to Other Commodities ......................................... 25 

Conclusions ........................................................................................................................................................... 26 

Recommendations ................................................................................................................................................ 26 

Appendix A: List of screened veterinary drug residues ........................................................................................ 29 

Appendix B: List of screened pesticides................................................................................................................ 30 

Appendix C: Determining proportion of Siluriformes fish servings ...................................................................... 31 

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Siluriformes fish data summary 29 March 2022 

Executive Summary 

Introduction 

On December 2, 2015, FSIS published the final rule “Mandatory Inspection of Fish of the Order Siluriformes 

and Products Derived from Such Fish” (80 FR 75590) that establishes a mandatory inspection program for 

these fish and for products derived from these fish, including imported fish products. The risk assessment that 

informed this rule identified various hazards that could be present in Siluriformes fish such as pesticides, 

veterinary drugs, and other chemical residues. The risk assessment identified Salmonella as the primary 

microbial hazard likely to be present with an estimated 2,400 illnesses attributed per year. FSIS began testing 

raw Siluriformes products for chemical residues, speciation, and Salmonella in May 2016. Under the U.S. 

National Residue Program (NRP), FSIS conducts testing for approved and unapproved veterinary drugs, 

pesticides, and environmental contaminants known or suspected to be present in food animals. In addition, 

FSIS collects samples to monitor for the presence of Salmonella in raw Siluriformes fish. 

Scope 

This report includes five years of both domestic and import testing data for raw Siluriformes products for 

chemical residues (veterinary drugs, dyes, pesticides, and metals) and Salmonella. The years covered are fiscal 

years (FY) 2016 through 2020. Some recent developments related to Siluriformes testing for chemical residues 

are excluded from this report, namely, testing 16 per- and polyfluoroalkyl substances (PFAS) beginning in FY 

2021, the results of the 2018 Dioxin Survey that include Siluriformes samples, and detections of semicarbazide 

(SEM) in imported Siluriformes. Additionally, in FY 2020, FSIS expanded National Antimicrobial Resistance 

Monitoring System (NARMS) testing to include Siluriformes fish. FSIS intends to publish additional results when 

sufficient data is collected to conduct a meaningful analysis of changes over time. 

Purpose 

In 2019, FSIS published the Strategic Evaluation of Sampling Resources (SASR). The underlying premise of that 

evaluation was that FSIS sampling only fulfills its purpose when the data it generates is used by the Agency. As 

of the end of fiscal year (FY) 2020, FSIS has tested raw Siluriformes products for five consecutive years. To fulfill 

the premise of the SASR evaluation—and to routinely review FSIS testing data and utilize that data in Agency 

decision-making—this report summarizes those five years of Siluriformes testing and provides 

recommendations for future FSIS sampling activities related to raw Siluriformes products based on the data. 

Overall Findings 

By the end of FY 2020, 10,116 samples had been collected and analyzed since FSIS began Siluriformes testing in 

May 2016. Samples were submitted for either microbiological testing or chemical residue testing. 

Chemical residue data analysis was divided into separate sections based on analytical methods: dyes, multiclass residue method, nitrofurans, pesticides, and metals. 

The residue detection rate has declined since Siluriformes testing began. For example, at the beginning of the 

program over 7% of samples tested positive for dyes. That value fell to less than 1% after testing began and 

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Siluriformes fish data summary 29 March 2022 

has remained low. Other veterinary drugs were verified to have detection rates below 1% throughout the 

testing program. For contaminants such as pesticides and metals, a disproportionate number of positive tests 

come from wild-caught Siluriformes fish where exposure cannot be controlled. Nevertheless, less than 1% of 

tests were positive for pesticides. Of the metals detected, most positive tests were for metals not of 

toxicological concern. For metals of toxicological concern, tested samples had levels that were either below 

the Environmental Protection Agency (EPA) limits or below values set by other countries for their imports. 

With regards to Salmonella, FSIS testing indicates that domestic Siluriformes fish have an average of 3.53 

percent positive from FY 2016 to FY 2020. Imported Siluriformes fish have an average 0.32 percent positive 

from FY 2016 to FY 2020. This difference may be attributed to imported Siluriformes fish typically being frozen, 

whereas domestic Siluriformes fish are typically fresh. While Salmonella is present on Siluriformes fish, there is 

limited data to support Siluriformes fish attribution to any Salmonella illnesses or outbreaks, except for an 

outbreak identified 30 years ago. Most Siluriformes fish are consumed fully cooked, which could explain the 

limited illnesses and outbreaks associated with this commodity. Based on consumer cooking practices, lack of 

recent outbreaks attributed to Siluriformes fish, and low percent positives, Siluriformes fish appear to present 

a low risk to public health. 

For the low number of estimated Salmonella illnesses attributed to Siluriformes fish, FSIS is greatly oversampling Siluriformes fish compared to other products. Two different attribution models resulted in current 

estimates of 930 and 1,080 annual illnesses due to Salmonella in Siluriformes. Changes in consumer cooking 

practices or in the processing environment (to where Siluriformes fish have a higher Salmonella percent 

positive) may alter the public health significance. 

Recommendations 

The following recommendations are made with the intent to better understand the risk posed by possible 

contaminants in Siluriformes fish: 

1. Develop a research priority for examining the effect of freezing on recovery of Salmonella from 

Siluriformes using FSIS methods. Different studies using different animal products yield different 

results. Knowing the log10 reduction expected from freezing would allow FSIS to better evaluate results 

from imported frozen Siluriformes. 

2. Consider suspending current FSIS Salmonella sampling in Siluriformes based on the updated illness 

estimates from the attribution-based risk assessment, the low overall occurrence of Salmonella in FSIS 

Siluriformes sampling results, and the absence of outbreaks attributable to Siluriformes. 

3. Conduct further analysis (speciation) of positive arsenic samples to verify the presence of organic 

arsenic rather than inorganic arsenic. This would increase confidence in the safety of FSIS inspected 

product. 

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Siluriformes fish data summary 29 March 2022 

Background 

History 

On December 2, 2015, FSIS published the final rule “Mandatory Inspection of Fish of the Order Siluriformes 

and Products Derived from Such Fish” (80 FR 75590) that establishes a mandatory inspection program for 

Siluriformes fish and for products derived from these fish, including imported Siluriformes fish products. The 

final rule explains that because these fish are amenable species under the Federal Meat Inspection Act (FMIA) 

(21 U.S.C. 601(w)(2)), the inspection program for these fish is part of FSIS’ meat inspection program. 

2015 Risk Assessment 

FSIS published a risk assessment that informed this final rule in 2012. The assessment was updated in 2015. 

The risk assessment identified various chemical hazards that could be present in Siluriformes fish such as 

pesticides and veterinary drugs. The risk assessment also identified microbial hazards. The risk characterization 

focused on illnesses from Salmonella. The main objectives of the risk assessment were to estimate the annual 

numbers of human salmonellosis cases from Siluriformes with its accompanying uncertainty and to estimate 

the potential number of cases that might be avoided following implementation of an FSIS inspection program. 

Salmonella 

Regarding Salmonella, the 2015 risk assessment noted: 

“Several bacterial pathogens have been associated with farmed-raised fish [1]. Because Siluriformes is 

typically cooked prior to consumption, Siluriformes-associated bacteria do not routinely present 

problems of public health concern [2]. Therefore, defining a specific pathogen as a microbiological 

hazard based on epidemiological data is a challenge. 

Salmonella is a potential microbial hazard for aquatic environments and, thus, may be a concern with 

respect to fish products. Non-typhi Salmonella are regarded as one of the higher-priority hazards 

because the general burden of illness from this pathogen in the U.S. remains a concern. There is 

evidence that at least one outbreak of human salmonellosis may have been related to Siluriformes 

consumption. Specifically, the CDC surmised that an outbreak of 10 cases of salmonellosis (Salmonella 

hadar) at a restaurant in 1991 may have been caused by Siluriformes consumption [3]. Additional 

outbreaks or illnesses specifically attributed to Salmonella in Siluriformes were not identified in the 

literature review. No outbreaks or illnesses of Salmonella in Siluriformes have been reported to FSIS 

since 2016, when FSIS implemented mandatory inspection. 

Salmonella was reported in 21% of 153 aquaculture catfish collected from aquaculture ponds and 

retail markets [4] and can be harbored within catfish for 30 days after exposure to high levels [5]. 

McCaskey et al. found Salmonella on 2.3% of 220 fillets sampled from three processing plants [6]. 

Heinitz et al. reported FDA Salmonella testing from imported (11,312 samples) and domestic (768) 

seafood samples tested from 1990 to 1998 [7]. They found that 10% of imported and 2.8% of domestic 

raw seafood was positive for Salmonella. For Fin Fish/Skin Fish in that study, the percent positive was 

12.2% and 1.3% for imported and domestic, respectively. An examination of FDA seafood import 

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Siluriformes fish data summary 29 March 2022 

refusal data from 1998-2004 identified Salmonella contamination to be the most frequent violation in 

catfish (41.91% of violation categories) [8].” 

Salmonella Illness Estimates from 2015 Risk Assessment 

The 2015 risk assessment used two different methods to estimate illnesses from Salmonella in Siluriformes 

fish. One method was to develop a mechanistic model that considered Salmonella concentration on fish, 

methods of cooking, serving size, and dose response. This mechanistic model yielded an estimate of 2,308 

illnesses annually. A boundary analysis of possible input ranges yielded a lower bound of 100 illnesses and an 

upper bound of 16,000 illnesses. 

The other method used an attribution model. This model was based on how many Salmonella illnesses occur 

annually and how many of those could be attributed to Siluriformes based on reported outbreaks. This method 

yielded an estimate of 2,400 illnesses with a lower limit of 280 and an upper limit of 6,700. 

Current Inspection/Testing Program Features 

FSIS conducts testing on raw Siluriformes fish products for chemical residues, speciation, and Salmonella. This 

testing ensures that the product is not adulterated with violative chemical residues. It also ensures the product 

is not misbranded based on species testing. In addition, FSIS monitors for the presence of Salmonella in raw 

Siluriformes fish products. Salmonella is not considered an adulterant in raw products, but test results can be 

used to monitor the effectiveness of the inspection program. 

Domestic 

Domestic Siluriformes fish are sampled according to FSIS Directive 14,010.1, Speciation Residue and Salmonella 

Testing of Fish of the Order Siluriformes from Domestic Establishments. Eligible samples include single 

ingredient, intact samples. Multi-ingredient (including breaded products) and non-intact products (e.g., 

vacuum-tumbled, injected) are not eligible for testing. 

Import 

Imported Siluriformes fish are sampled according to FSIS Directive 14,100.1, Speciation, Residue, and 

Salmonella Testing of Fish of the Order Siluriformes at Official Import Inspection Establishments. Eligible 

samples include intact samples. Non-intact products (e.g., vacuum-tumbled, injected) and breaded products 

are not eligible for testing. 

Domestic vs Import Volume 

For domestic samples FSIS collects estimated daily volume and production days per month when samples are 

collected. Monthly domestic volume is estimated by multiplying estimated daily volume (the midpoint of a 

selected range) by production days for unique month/establishment combinations. Information on whether 

the fish were wild-caught or farm-raised is usually available. For imported samples, product lot volumes are 

given. Using these values for FY 2019 and FY 2020, domestic Siluriformes fish represented about 70% of total 

volume (7% wild-caught) and imported Siluriformes fish about 30%. The National Agricultural Statistics Service 

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Siluriformes fish data summary 29 March 2022 

estimates domestic sales of about 348 million pounds in CY 2019 and 324 million pounds in CY 2020 (Catfish 

Production 02/08/2021 (usda.gov)). The National Oceanic and Atmospheric Administration estimates imports 

of 200 million pounds in 2019 and 209 million pounds in 2020 (HOME (noaa.gov)). 

Methods/Approach 

Microbiological Testing 

Inspection program personnel collect Siluriformes fish samples at domestic establishments (per FSIS Directive 

14,010.1) and at official import inspection establishments (per FSIS Directive 14,100.1). Samples are shipped 

overnight to one of three field service laboratories to be analyzed. Laboratory personnel analyze raw 

Siluriformes fish samples for Salmonella according to Chapter 4 of the Microbiology Laboratory Guidebook. 

Analysts aseptically cut a 25 ± 6.5 g sample and combine it with 225 ± 4.5 mL of buffered peptone water (BPW) 

in a sterile bag. After hand stomaching, the sample is incubated at 35 ± 2°C for 22-26 hours. Enrichments are 

screened molecularly. Salmonella isolated from positive samples is confirmed phenotypically. The isolates are 

further characterized by antimicrobial susceptibility testing and whole genome sequencing. Serotype is then 

determined from the genomic data. 

Chemical Residue Testing 

An essential aspect of food safety in meat, poultry, and egg products is the control of residues that may result 

from the use of veterinary drugs and pesticides, or from exposure to environmental contaminants. Under the 

NRP, four analytical methods were used by FSIS to test for approximately 250 different veterinary drugs, 

pesticides, and environmental contaminants in Siluriformes fish. Testing includes drugs approved by the Food 

and Drug Administration (FDA) for use in fish as well as unapproved drugs that FSIS has a basis for believing, 

due to FSIS’ familiarity with U.S. aquatic production, are available to and could be improperly used by U.S. 

Siluriformes fish producers. A violation occurs when an FSIS laboratory detects a chemical compound at a level 

that exceeds an established tolerance or action level for that compound, or if the specific type of chemical 

compound does not have an established tolerance. Violative residues render Siluriformes fish product 

adulterated under the FMIA. 

Literature Review 

Contaminants in the Environment 

Chemical contamination from manufacturing, runoff, effluent discharges, and other anthropogenic activities is 

a worldwide concern. Although some chemicals are transformed in the environment, chemicals or their 

metabolite residues may form persistent deposits in sediment [9, 10]. Siluriformes fish are benthic, or bottomdwelling, feeders. As such, they are exposed to residues in both water and sediment. Residues can accumulate 

in the muscle tissue or fat and be potentially hazardous to wildlife and human health, depending on the 

amount of fish consumed [9, 11]. Watanabe et al. (2003) analyzed fish tissues for chemical contamination in 

the lower Mississippi River [10]. The resulting risk assessment named twelve species of concern; seven of them 

were benthic feeders, including three species of Siluriformes fish [12]. As residues increase in the environment, 

there is an increased risk of interference in biological processes by altering the composition of bacterial 

communities [13]. 

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Aquaculture 

Many fish belonging to the order Siluriformes are resilient and adaptable to harsh conditions, including low 

dissolved oxygen, that are common in aquaculture ponds. Their hardiness, growth rate, feed conversion 

efficiency, and ease of reproduction make them ideal candidates for aquaculture. Siluriformes fish constitute 

60% of all aquaculture production in the U.S. [14]. However, farmed fish may still be exposed to contaminants 

through runoff, soil seepage, or wind [9]. 

Farmed fish may also be exposed to bacterial or chemical contaminants through feed [15, 16]. Salmonella has 

been found in multiple feed ingredients and in feed processing establishments. Salmonella strains in feed tend 

to be more heat resistant due to the drying process. However, if the dose is small, the risk of colonization in 

the fish is low [15]. 

Overuse of antibiotics and the resulting residues in the environment contribute to increases in antibiotic 

resistant bacteria. In aquaculture, several antibiotics are approved to treat disease. Triphenylmethane dyes, 

such as malachite green and crystal violet, have been used in aquaculture to prevent and control fungal 

growth, since the early 1900s [17]. Increased exposure to antibiotic resistant bacteria may lead to treatment 

failure in both animals and humans [18]. 

Schar et al. (2020) estimated that over 10,000 tons of antimicrobials were used in aquaculture globally in 2017 

and that 8.3% of those compounds were applied to farmed Siluriformes fish [13]. Almost 90% of global 

aquaculture production is in Asia but it is expanding in developing nations. By 2030, it is possible that the 

number of antimicrobials used in aquaculture could increase by 33%. Advancements in husbandry and nonpharmaceutical interventions could reduce the potential environmental impacts [13]. 

Salmonella in Siluriformes Fish Production 

As in all food processing, the proper implementation of Hazard Analysis and Critical Control Point (HACCP) is 

essential to reduce the risk of contamination, either directly or indirectly through cross-contamination. Once 

Salmonella forms a biofilm, it is difficult to eliminate from the processing environment. Although Siluriformes 

fish mucus has been shown to promote the growth of Salmonella, there are no published articles discussing 

persistent Salmonella in Siluriformes fish production [19]. Love et al. (2021) analyzed various hazards along the 

supply chain and showed that Siluriformes fish are safer across a broad category of risks including microbial 

risks than most other aquaculture species [20]. 

Outbreak Data 

While Salmonella is present on Siluriformes fish, there is limited data to support Siluriformes fish attribution to 

any Salmonella illnesses or outbreaks, except for an outbreak identified 30 years ago [21]. The Interagency 

Food Safety Analytics Collaboration's (IFSAC) multi-year outbreak data model estimates that 2.1% of 

Salmonella can be attributed to fish of any kind. This model gives more weight to outbreaks that occurred in 

the last five years (IFSAC 2020). According to CDC's National Outbreak Reporting System (NORS), 655 

foodborne outbreaks in the U.S. have been attributed to fish of any taxonomic order between 2000 and 2018. 

In all fish, 43% of attributed outbreaks were linked to scombroid fish poisoning, or a buildup of histamine in 

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Siluriformes fish data summary 29 March 2022 

fish tissues because of bacterial activity; poisoning of this type is due to temperature abuse of the product. 

Toxins produced by harmful algae blooms contributed 39.5% of the outbreaks. One outbreak was linked to 

heavy metal contamination. Nineteen of the outbreaks were linked to Salmonella. Of these, three were 

associated with tuna that may have been consumed raw. Eleven of the outbreaks could not specifically be 

linked to fish as the dish had multiple ingredients. For example, four were connected to gefilte fish, a prepared 

dish that also includes egg. The remaining outbreaks were associated with red snapper, smoked salmon, 

striped bass, flounder, codfish, tilapia, or an unspecified finfish species. There were four total outbreaks 

attributed to Siluriformes fish; two were of unknown etiology, one was linked to enterotoxigenic Escherichia 

coli and another was due to an unknown chemical or toxin. There were no known outbreaks of Salmonella 

attributed to Siluriformes fish. 

Data 

Laboratory test results for both chemical residue and pathogen testing are stored in the Public Health 

Information System. Data were summarized using Microsoft Excel and the results are provided below. 

Results 

General Testing Results 

Since FSIS began Siluriformes fish testing, in May 2016, 10,116 samples were collected and analyzed. Of those, 

4,253 samples were from domestic Siluriformes fish and 5,863 were from imports (Table 1). Samples were 

submitted for either microbiological testing or chemical residue testing. 

Table 1. Types of samples collected for fish of the order Siluriformes fish in fiscal years 2016 through 2020. 

Type of sample Number 

Domestic 4,253 

Import 5,863 

Total 10,116 

As FSIS began incorporating testing of Siluriformes fish, relatively few samples were collected in the first two 

years of the program. Gradually, testing numbers increased in FY 2019 and FY 2020 (Table 2). By volume, 

proportionally more samples are collected for imported samples than for domestic samples, though it should 

be noted that samples from imported product represent only that specific lot while samples from domestic 

product are more representative of an ongoing process. 

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Table 2. Types of samples collected for fish of the order Siluriformes fish in fiscal years 2016 through 2020. 

Domestic Import 

FY Microbiological Chemical residue Microbiological Chemical residue Total 

2016 77 78 42 84 281 

2017 192 201 213 436 1,042 

2018 613 636 221 580 2,050 

2019 608 618 745 1,563 3,534 

2020 607 623 652 1,327 3,209 

Total 2,097 2,156 1,873 3,990 10,116 

Chemical Residues 

Analysis of chemical residue data was divided into separate sections based on analytical methods: dyes, multiclass residue method, nitrofurans, pesticides, and metals. For some domestic samples we could determine 

whether the source was farm-raised or wild-caught. Based on those samples, FSIS estimates that about 7% of 

domestic production comes from wild-caught Siluriformes fish. In cases where a violation is reported, FSIS 

shares the violation data with the EPA, as well as with the FDA when the FDA has on-farm jurisdiction. Because 

FSIS began testing for additional contaminants such as PFAS, semicarbazide, and dioxins in FY 2021, those 

results are not included in this report which covers only from FY 2016 to FY 2020. FSIS intends to publish these 

results when sufficient data is collected to conduct a meaningful analysis of changes over time. 

Dyes 

FSIS currently tests for the presence of the dyes crystal violet and malachite green. Both of these dyes have 

been used for their antimicrobial properties [22]. Due to their carcinogenicity, mutagenicity, and teratogenicity 

potentials, many countries, including the United States, have prohibited the use of these dyes in feed and 

aquaculture production [23]. Detection of crystal violet and malachite green, with their respective metabolites 

(leucocrystal violet and leucomalachite green), results in a residue violation in Siluriformes fish. 

From FY 2016 to FY 2020, 3,147 Siluriformes fish samples were tested for dyes. Of these, 30 (0.95%) were 

violative. Samples of imported Siluriformes fish were twice as likely to have violative levels of dyes as domestic 

samples were (Table 3); although the difference was not statistically significant (p=0.07). 

Table 3. Results of testing for dyes in domestic vs. imported Siluriformes fish. 

Violative Non-Detect Total % Pos 

Domestic 6 1,121 1,127 0.53% 

Imported 24 1,996 2,020 1.19% 

Total 30 3,117 3,147 0.95% 

For some domestic samples, FSIS identified whether the source was farm-raised or wild-caught (Table 4). For 

those Siluriformes fish for which a source was identified as either farm-raised or wild-caught, there was no 

significant difference in the percentage of violative dye residues (p=0.74). 

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Siluriformes fish data summary 29 March 2022 

Table 4. Results of testing for dyes in farm-raised vs. wild-caught Siluriformes fish (domestic only). 

Source Violative Non-Detect Total % Pos 

Farm 2 525 527 0.38% 

Wild 3 585 588 0.51% 

Total 5 1,110 1,115 0.45% 

Of the 30 dye violations, 22 were identified in the first two years (FY 2016 and FY 2017) of the testing program 

(Table 5). Another seven samples were found violative in 2018. Only one sample has been found violative since 

then. 

Table 5. Results of testing for dyes in all Siluriformes fish by fiscal year (FY). 

FY Violative Non-Detect Total % Pos 

2016 4 69 73 5.48% 

2017 18 269 287 6.27% 

2018 7 798 805 0.87% 

2019 1 1,033 1,034 0.10% 

2020 0 948 948 0.00% 

Total 30 3,117 3,147 0.95% 

Table 6 and Table 7 show the yearly results for domestic and imported Siluriformes fish. 

Table 6. Results of testing for dyes in domestic Siluriformes fish by fiscal year (FY). 

FY Violative Non-Detect Total % Pos 

2016 1 30 31 3.23% 

2017 1 77 78 1.28% 

2018 4 466 470 0.85% 

2019 0 256 256 0.00% 

2020 0 292 292 0.00% 

Total 6 1,121 1,127 0.53% 

Table 7. Results of testing for dyes in imported Siluriformes fish by fiscal year (FY). 

FY Violative Non-Detect Total % Pos 

2016 3 39 42 7.14% 

2017 17 192 209 8.13% 

2018 3 332 335 0.90% 

2019 1 777 778 0.13% 

2020 0 656 656 0.00% 

Total 24 1,996 2,020 1.19% 

Multi-Residue Method (MRM) 

The Federal Food Drug and Cosmetics Act (FFDCA), 21 U.S.C. 301 et seq., authorizes FDA to establish 

tolerances, regulatory limits, and other limitations or specifications for animal drugs. Under the NRP, FSIS 

conducts testing for more than 100 approved and unapproved veterinary drugs potentially present in food 

animals (Appendix A). 

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Siluriformes fish data summary 29 March 2022 

Between the periods of FY2016 and FY 2020, 4,058 Siluriformes fish samples were analyzed for veterinary 

residues using the multi-residue method (MRM) (Table 8). Table 8 shows the number of samples analyzed by 

year. 

Table 8. Number of tests using the multi-residue method for Siluriformes fish by fiscal year (FY) 

FY Tests 

2016* 120 

2017 414 

2018 972 

2019 1,343 

2020* 1,209 

Total 4,058 

*Two violations were reported in 4,058 Siluriformes fish samples from 2016 thru 2020 

Since implementation, FSIS has reported two veterinary drug violations (0.05%). In FY 2016, FSIS reported a 

finding of enrofloxacin in an imported Siluriformes fish product. In 2020, lasalocid was detected in a domestic 

farm-raised Siluriformes fish. Violations were reported to the FDA. 

Nitrofurans 

In 1991, the FDA prohibited the use of all nitrofuran antibiotics for use in food-animals, including aquaculture 

products. Nitrofuran antibiotics have been reported to initiate tumor growth, by the formation of 

hydroxylamine derivatives that cause oxidative damage to DNA [24]. Therefore, similar to the dyes, detection 

of nitrofurans (and metabolites) in Siluriformes fish product is considered violative. FSIS’ current method can 

screen and confirm for parent compounds and metabolites of furazolidone, furaltadone, nitrofurantoin, and 

nitrofurazone. 

Between the periods of FY 2016 and FY 2020, 2,658 Siluriformes fish samples were tested for nitrofuran 

antibiotics (Table 9). Table 9 shows the number of samples collected by year. Of these, there were only two 

violative samples (0.08%). Nitrofurazone and furazolidone were reported in product imported in FY 2016 and 

FY 2017, respectively. 

Table 9. Number of tests for nitrofurans for Siluriformes fish by fiscal year (FY) 

FY Tests 

2016* 89 

2017* 350 

2018 411 

2019 1,094 

2020 714 

Total 2,658 

*Two violations were reported in 2,658 Siluriformes fish samples from 2016 thru 2020. 

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Pesticides 

Under the Acts, FSIS-regulated product is adulterated “if it is, in whole or in part, a raw agricultural commodity 

and such commodity bears or contains a pesticide chemical which is unsafe within the meaning of section 

346a” of the FFDCA. EPA establishes tolerance levels for many registered pesticides, which can be found in 

Title 40 of the Code of Federal Regulations (CFR). Similar to veterinary drugs, pesticide residues are considered 

violative if the detected level exceeds applicable EPA tolerance. Under the NRP, each sample is screened for 

more than 108 approved and unapproved pesticide residues (Appendix B). 

From FY 2016 to FY 2020, 2,866 Siluriformes fish samples were tested for pesticides. Pesticide residues were 

detected in 45 (1.57%) domestic and imported Siluriformes fish products (Table 10). Of these, 19 (0.66%) 

Siluriformes fish samples contained pesticide residues that either exceeded an EPA tolerance or were detected 

in the absence of a tolerance (Table 11). Domestic Siluriformes fish samples were five times more likely to have 

pesticides detected as imported samples and nearly three times more likely to be violative. Both these 

differences were statistically significant (p<0.01, p<0.05, respectively). 

Table 10. Non-violative or violative detections of pesticides in domestic vs. imported Siluriformes fish. 

NonDetect Detect Total % Pos 

Domestic 32 870 902 3.55% 

Import 13 1,951 1,964 0.66% 

Total 45 2,821 2,866 1.57% 

Table 11. Violative detections of pesticides in domestic vs. imported Siluriformes fish. 

Violative Non-Detect Total % Pos 

Domestic 11 891 902 1.22% 

Import 8 1,956 1,964 0.41% 

Total 19 2,847 2,866 0.66% 

There were 55 total non-violative and violative detections of pesticides among 45 samples. Ten of the 45 

samples had two different pesticides detected. Nineteen of the 45 samples had at least one result that was 

violative. In 3 of the samples there were 2 violative detections for a total of 22 violations among 19 samples. 

Thus, of the 55 detections, 33 represented non-violative detections and 22 violative detections. Table 12 

shows pesticide non-violative detections alone and Table 13 shows pesticide violative detections alone. As 

noted above multiple pesticide residues may be associated with the same Siluriformes fish samples. 

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Table 12. Frequency of pesticide non-violative detections identified in all Siluriformes fish 

Pesticide Detections 

DDT and Metabolites 14 

Chlorpyrifos 10 

Chlordane Cis and Trans 5 

p DDE 1 

Nonachlor Trans 1 

Diuron 1 

Dieldrin 1 

Total 33 

Table 13. Frequency of pesticide violative detections identified in all Siluriformes fish 

Pesticide Violative tests 

Metolachlor 6 

Atrazine and Metabolites 5 

Fipronil 4 

Chlorpyrifos 3 

HCB 1 

Profenofos 1 

Fipronil sulfide 1 

Fipronil desulfinyl 1 

Total 22 

For most domestic samples, FSIS identified whether the source was farm-raised or wild-caught (Table 14 and 

Table 15). The proportion of positive samples was about twice as high in wild-caught compared to farm-raised 

fish for both non-violative and violative detections (p<0.05) and for violative detections alone, although the 

difference was not statistically significant for violative detections alone. 

Table 14. Non-violative and violative pesticide detections in farm-raised vs. wild-caught Siluriformes fish (domestic only). 

Source Detect Non-Detect Total % Pos 

Farm 10 377 387 2.58% 

Wild 23 408 431 5.34% 

Total 33 785 818 4.03% 

Table 15. Violative pesticide detections in farm-raised vs. wild-caught Siluriformes fish (domestic only). 

Source Violative Non-Detect Total % Pos 

Farm 3 384 387 0.78% 

Wild 8 423 431 1.86% 

Total 11 807 818 1.34% 

When farm-raised and wild-caught were assessed together, there was no significant difference over time for 

the percentage of non-violative and violative detections (Table 16) or for violative detections alone (Table 17) 

for FY 2016 to FY 2020. 

15 
0 

22 

0 

1 0 0 

27 0 

0 

43 1 

0 01 DC 

36 1 

0 

39 

0 1 0 0 

3 

0 13 6 

0 0 

3 0 

0 

Siluriformes fish data summary 29 March 2022 

Table 16. Non-violative and violative detections of pesticides for all Siluriformes fish by fiscal year (FY). 

FY Detection Non-Detect Total % Pos 

2016 0 89 89 0.00% 

2017 4 344 348 1.15% 

2018 6 405 411 1.46% 

2019 19 1,075 1,094 1.74% 

2020 16 908 924 1.73% 

Total 45 2,821 2,866 1.57% 

Table 17. Violative pesticide detections in all Siluriformes fish by fiscal year (FY). 

FY Violative Non-Detect Total % Pos 

2016 0 89 89 0.00% 

2017 4 344 348 1.15% 

2018 1 410 411 0.24% 

2019 7 1,087 1,094 0.64% 

2020 7 917 924 0.76% 

Total 19 2,847 2,866 0.66% 

Figure 1 shows the geographic distribution of pesticide testing results for domestic samples. In general, 

positive tests occurred proportionally to testing. The differences among states were not statistically significant 

(p > 0.40). 

Figure 1. Number of pesticide samples collected (middle value in each circle), number of total non-violative and violative detections 

(bottom value), and number of violative detections (top value) by state for both farm-raised and wild-caught Siluriformes fish. 

16 
Siluriformes fish data summary 29 March 2022 

Metals 

As part of the NRP, FSIS analyzes Siluriformes fish samples for the presence of various essential (required for 

human health) and non-essential metals, which do not have discrete regulatory values to be enforced. 

Therefore, metal detections do not adulterate the product. The analyzed metals include aluminum, arsenic1

, 

barium, boron, cadmium, chromium, cobalt, copper, iron, lead, manganese, molybdenum, nickel, selenium, 

strontium, thallium, vanadium, and zinc. 

From FY 2016 to FY 2020, 3,027 samples were tested for metals. Of these, 223 (7.37%) samples had detectable 

metals. Domestic samples were almost three times as likely to have detectable metals as imported samples 

(Table 18). This difference was statistically significant (p<0.01). 

Table 18. Non-violative detections of metals in domestic vs. imported Siluriformes fish 

NonDetect Detect Total % Pos 

Domestic 136 958 1,094 12.43% 

Import 87 1,846 1,933 4.50% 

Total 223 2,804 3,027 7.37% 

For many of the domestic samples, FSIS identified whether the source was farm-raised or wild-caught (Table 

19). 

Table 19. Non-violative detections of metals in farm-raised vs. wild-caught Siluriformes fish (domestic only). 

NonSource Detect Detect Total % Pos 

Farm 16 377 393 4.07% 

Wild 118 457 575 20.52% 

Total 134 834 968 13.84% 

The proportion of samples with detectable metal levels was five times higher in wild-caught compared to farmraised fish (p<0.01). Although domestic Siluriformes fish identified as wild-caught accounted for only 575 out 

of 3,027 samples (19.0%), they accounted for 118 out of 223 total positive tests (52.9%). Since FY 2016, the 

percentage of metal detection has been rising steadily (Table 20). Domestic sample detections account for that 

increase (Table 22 and Table 22). 

1 Arsenic as will be noted later is generally in an organic form and is of little toxicological concern. 

17 
Siluriformes fish data summary 29 March 2022 

Table 20. Non-violative detections of metals in all Siluriformes fish by fiscal year (FY). 

NonFY Detect Detect Total % Pos 

2016 2 55 57 3.51% 

2017 16 271 287 5.57% 

2018 51 754 805 6.34% 

2019 71 948 1,019 6.97% 

2020 83 776 859 9.66% 

Total 223 2,804 3,027 7.37% 

Table 21. Non-violative detections of metals in domestic Siluriformes fish by fiscal year (FY). 

NonFY Detect Detect Total % Pos 

2016 0 23 23 0.00% 

2017 3 75 78 3.85% 

2018 47 423 470 10.00% 

2019 37 220 257 14.40% 

2020 49 217 266 18.42% 

Total 136 958 1,094 12.43% 

Table 22. Non-violative detections of metals in imported Siluriformes fish samples by fiscal year (FY). 

NonFY Detect Detect Total % Pos 

2016 2 32 34 5.88% 

2017 13 196 209 6.22% 

2018 4 331 335 1.19% 

2019 34 728 762 4.46% 

2020 34 559 593 5.73% 

Total 87 1,846 1,933 4.50% 

As noted in Table 19, wild-caught Siluriformes fish account for most samples that were detected for metals. 

Table 23 shows that the percentage of detected samples in wild-caught Siluriformes fish has increased since 

2018. 

Table 23. Non-violative detections of metals in wild-caught Siluriformes fish samples by fiscal year (FY). 

FY Zero One Two Three Total % Pos 

2017 3 1 -- -- 4 25.0% 

2018 208 38 1 -- 247 15.8% 

2019 119 26 5 1 151 21.2% 

2020 127 35 11 -- 173 26.6% 

Total 457 100 17 1 575 20.5% 

Metals detected in Siluriformes fish are shown in Table 24. The total number of metal detection (261) is higher 

than the total number of sample detections (223) because some samples may have multiple metal detections 

(Table 20). For both domestic and imported samples of Siluriformes fish, manganese accounts for nearly 47% 

18 
Siluriformes fish data summary 29 March 2022 

of the metal detection. As an essential metal, manganese is important in enzyme functions such as 

metabolism, regulation of cellular energy, reproduction, and bone and connective tissue growth [25]. 

Table 24. Frequency of metals identified in all Siluriformes fish 

Metal Positive tests 

Manganese 124 

Arsenic 45 

Strontium 17 

Zinc 17 

Selenium 14 

Iron 14 

Lead 12 

Nickel 7 

Boron 4 

Cadmium 2 

Chromium 2 

Copper 1 

Aluminum 1 

Molybdenum 1 

Barium 0 

Cobalt 0 

Thallium 0 

Vanadium 0 

Total 261 

Similar to manganese, aluminum [26], boron [27], copper [28], iron, molybdenum [25], selenium [29], and zinc 

[30], are all considered essential metals with important functions in the human body. Detection of essential 

metals does not warrant further analysis as they do not pose any potential public health concerns. Nonessential metals that may pose a concern to human health (arsenic, cadmium, chromium, lead, nickel, and 

strontium) do warrant further analysis. These are discussed individually below. 

Arsenic 

Second to manganese, arsenic was detected most frequently. From FY 2016 to FY 2020, FSIS reported 45 

arsenic non-violative detections out of 1,747 Siluriformes fish samples, meaning more than 97.4% of samples 

had no detectable arsenic. As with other metals, arsenic was more likely to be found in domestic fish than in 

imported fish (Table 25 and Table 26). When the source was known, arsenic was only detected in wild-caught 

Siluriformes fish (Table 26). Domestic wild-caught Siluriformes fish accounted for 40 of the 45 total arsenic 

non-violative detections reported. 

Table 25. Levels of arsenic detected in imported Siluriformes fish for fiscal years 2016-2020. 

Level (ppb) Unknown Farm-raised Wild-caught 

Not Detected 1,196 39 --

100-200 4 -- --

200-300 1 -- --

19 
Siluriformes fish data summary 29 March 2022 

Table 26. Levels of arsenic detected in domestic Siluriformes fish for fiscal years 2016-2020. 

Level (ppb) Unknown Farm-raised Wild-caught 

Not Detected 8 182 277 

100-200 -- -- 29 

200-300 -- -- 9 

300-400 -- -- 2 

Arsenic detection levels ranged from 100 to 322 ppb. FSIS’ analytical method quantifies total chromium and 

does not distinguish between organic and inorganic arsenic. Although inorganic arsenic is a known carcinogen 

it constitutes only a fraction of the total arsenic found in fish muscle [31]. The FDA has not set an acceptable 

limit for arsenic in Siluriformes fish. The U.S. Agency for Toxic Substance and Disease Registry (ATSDR) 

reported that levels of arsenic in fish, crustaceans, and seaweed are associated with the organic forms and are 

considered to be of little toxicological concern [32]. It should also be noted that the Australia New Zealand 

Food Standards Code includes a 2 ppm (2000 ppb) standard for arsenic in fish, which is six times higher than 

the highest level detected among these samples. Given the extremely low rate of detections, any exposure to 

arsenic in Siluriformes fish products would be short in duration. FSIS will continue to monitor arsenic data to 

identify trends and determine whether additional actions are necessary. 

Strontium 

From FY 2016 to FY 2020, FSIS reported 17 strontium non-violative detections out of 2,935 Siluriformes fish 

samples (0.58%). There are no regulatory levels for strontium. 

Table 27. Levels of strontium detected in imported Siluriformes fish for fiscal years 2016-2020. 

Level (ppb) Unknown Farm-raised Wild-caught 

Not Detected 1,769 117 --

0-100 4 -- --

Table 28. Levels of strontium detected in domestic Siluriformes fish for fiscal years 2016-2020. 

Level (ppb) Unknown Farm-raised Wild-caught 

Not Detected 122 374 536 

0-100 -- 1 12 

Lead 

From FY 2016 to FY 2020, FSIS reported 12 lead non-violative detections in 2,941 Siluriformes fish samples 

(0.41%). Lead positives were detected in both imported (Table 29) and domestic (Table 30) samples. For 

imported fish, there were 8 samples with detectable lead levels out of 1,843 total samples (0.43%). For 

domestic fish, there were 4 detects for lead in 1,098 total samples (0.36%). When source information was 

available, there was no statistically significant difference between farm-raised and wild-caught lead detections. 

20 
Siluriformes fish data summary 29 March 2022 

Table 29. Levels of lead detected in imported Siluriformes fish for fiscal years 2016-2020. 

Level (ppb) Unknown Farm-raised Wild-caught 

Not Detected 1,719 116 --

0-100 6 2 --

Table 30. Levels of lead detected in domestic Siluriformes fish for fiscal years 2016-2020. 

Level (ppb) Unknown Farm-raised Wild-caught 

Not Detected 212 400 482 

0-100 -- 1 3 

While no reference dose is available for lead, the FDA has published an Interim Reference Level (IRL). The IRL is 

a daily exposure level likely to be associated with increasing the consumer’s blood level of concern. The IRL for 

lead is set for 3 μg/day for children and 12.5 μg/day for adults (16). The European Union (EU) and the 

Australian government have established a maximum level of 100 ppb for lead in most meats. Lead detection 

levels ranged from 17 to 88 ppb, far below what would constitute a violation in exported product. 

Nickel 

From FY 2016 to FY 2020, FSIS reported 7 nickel non-violative detections (0.23%) out of 2,986 Siluriformes fish 

samples (Table 31). 

Table 31. Results of testing for nickel in domestic vs. imported Siluriformes fish. Detection only, no violations 

NonDetect Detect Total % Pos 

Domestic 2 1,803 1,805 0.18% 

Import 5 1,903 1,908 0.26% 

Total 7 2,986 2,993 0.23% 

Food is the major source of nickel exposure, with an average intake for adults estimated to be 

approximately 100 to 300 μg per day [33, 34]. Nickel is an essential nutrient for some mammalian species and 

has been suggested to be essential for human nutrition. One animal study observed a significant decrease in 

the body and liver weights in rats when the animals were exposed to nickel at a concentration of 75 mg/kg/day 

[33]. 

Cadmium 

From FY 2016 to FY 2020, 3,119 Siluriformes fish samples were analyzed for cadmium. Of those, two cadmium 

non-violative detections (0.06%) were reported in one imported fish (Table 32) and one domestic wild-caught 

fish (Table 33). Therefore, more than 99.9% of samples had no detectable cadmium. 

Table 32. Levels of cadmium detected in imported Siluriformes fish for fiscal years 2016-2020. 

Level (ppb) Unknown Farm-raised Wild-caught 

Not Detected 1,903 123 --

0-100 1 -- --

21 
Siluriformes fish data summary 29 March 2022 

Table 33. Levels of cadmium detected in domestic Siluriformes fish for fiscal years 2016-2020. 

Level (ppb) Unknown Farm-raised Wild-caught 

Not Detected 132 387 572 

0-100 -- -- 1 

While the U.S. has not established regulatory levels for cadmium in meat, the European Union, Australia, and 

New Zealand have set a maximum level of 50 ppb. Only one of the samples tested (0.03 %) exceeded this level 

(imported sample at a level of 61.8 ppb). 

Chromium 

From FY 2016 to FY 2020, 3,088 Siluriformes fish samples were analyzed for chromium. Of those, two 

chromium positives (0.06%) were reported in one imported fish (Table 34) and one domestic wild-caught fish 

(Table 35). Therefore, more than 99.9% of samples had no detectable chromium. 

Table 34. Levels of chromium detected in imported Siluriformes fish for fiscal years 2016-2020. 

Level (ppb) Unknown Farm-raised Wild-caught 

Not Detected 1,903 123 --

0-100 1 -- --

Table 35. Levels of chromium detected in domestic Siluriformes fish for fiscal years 2016-2020. 

Level (ppb) Unknown Farm-raised Wild-caught 

Not Detected 121 379 560 

0-100 -- 1 --

Chromium typically occurs in the environment as naturally occurring chromium III, which is an essential metal, 

or as chromium VI which is a relatively toxic industrial contaminant. FSIS’ analytical method quantifies total 

chromium and does not distinguish between the two forms of chromium. In the World Health Organization’s 

2003 chromium review, the total chromium levels (both III and VI) of meat, fish, fruits, and vegetables ranged 

from < 10 to 1,300 ug/kg [35]. 

Salmonella 

From FY 2016 to FY 2020 there were 3,970 tests for Salmonella and 80 positives. The percentage of domestic 

positive samples was about eleven times higher than in imported samples (p<0.01). Only six of the positive 

samples came from imported product. 

Table 36. Results of testing for Salmonella in domestic vs. imported Siluriformes fish 

Positive Negative Total % Pos 

Domestic 74 2,023 2,097 3.53% 

Import 6 1,867 1,873 0.32% 

Total 80 3,890 3,970 2.02% 

Imported samples are typically frozen. This may explain the lower percent of positive samples. DiGirolamo et. 

al.(1970) showed a 2 log10 decrease in Salmonella Derby and Typhimurium in frozen oysters [36]. Dominguez 

and Schaffner (2009), reported noting the survival of Salmonella Kentucky and Typhimurium in frozen cooked 

22 
Siluriformes fish data summary 29 March 2022 

chicken nuggets and frozen raw chicken strips, though the cells incurred structural damage and did not grow 

well on selective media [37]. Dykes and Moorhead (2001) reported no decrease in Salmonella Brandenburg, 

Dublin, or Typhimurium in frozen beef trim [38]. A study specific to frozen Siluriformes fish could help 

determine the reason for the low Salmonella prevalence in imported samples and, if necessary, could help 

identify a testing method to better detect Salmonella in frozen samples. 

Of the 80 positive samples, serotype information was available for 27 (Table 37). 

Table 37. Salmonella serotypes in positive samples from all Siluriformes fish 

Serotype Number 

Hartford 6 

Rubislaw 4 

Senftenberg 3 

Oranienburg 1 

Minnesota 1 

Pomona 1 

Hvittingfoss 1 

Newport 1 

IIIb 17:z10:e,n,x,z15 1 

Orion var. 15+,34+ 1 

Gaminara 1 

Daytona 1 

Urbana 1 

Mbandaka 1 

Agbeni 1 

Virchow 1 

Miami 1 

Total 27 

For domestic Siluriformes fish for which source information was available, there was no difference in the 

percentage of positive Salmonella samples in farm-raised compared with that in wild-caught fish. 

Table 38. Results of testing for Salmonella in farm-raised vs. wild-caught Siluriformes fish (domestic only) 

Source Positive Negative Total % Pos 

Farm 25 717 742 3.37% 

Wild 30 896 926 3.24% 

Total 55 1,613 1,668 3.30% 

There was a higher percentage of positive samples in the first year of testing than in subsequent years. Since 

FY 2017 there has been no significant difference in the percentage of positive samples between each year. This 

applies to total samples and for domestic and import samples (Table 39, Table 40, and Table 41). 

23 
Siluriformes fish data summary 29 March 2022 

Table 39. Results of testing for Salmonella for all Siluriformes fish by fiscal year (FY). 

FY Positive Negative Total % Pos 

2016 8 111 119 6.72% 

2017 10 395 405 2.47% 

2018 15 819 834 1.80% 

2019 22 1,331 1,353 1.63% 

2020 25 1,234 1,259 1.99% 

Total 80 3,890 3,970 2.02% 

Table 40. Results of testing for Salmonella in domestic Siluriformes fish by fiscal year (FY). 

FY Positive Negative Total % Pos 

2016 8 69 77 10.39% 

2017 7 185 192 3.65% 

2018 15 598 613 2.45% 

2019 21 587 608 3.45% 

2020 23 584 607 3.79% 

Total 74 2,023 2,097 3.53% 

Table 41. Results of testing for Salmonella in imported Siluriformes fish by fiscal year (FY). 

FY Positive Negative Total % Pos 

2016 0 42 42 0.00% 

2017 3 210 213 1.41% 

2018 0 221 221 0.00% 

2019 1 744 745 0.13% 

2020 2 650 652 0.31% 

Total 6 1,867 1,873 0.32% 

Risk Characterization for Salmonella 

This report does not include an update of the mechanistic model found in the 2015 risk assessment. Such a 

model is beyond the scope of the current effort. That said, the attribution model in the 2015 risk assessment 

could be easily updated. This model was based on the number of Salmonella outbreaks reported to CDC from 

1990 through 2007. Out of 1,159 outbreaks in which a foodborne vehicle was identified, there was one 

outbreak in which Siluriformes fish was the likely source. Using an estimate of about 1.4 million Salmonella 

illnesses annually [39], the model estimated 2,400 annual illnesses with a lower limit of 280 and an upper limit 

of 6,700. 

To update this model, FSIS would add the number of outbreaks that have occurred since 2007 and apply the 

same equation applied in the 2015 risk assessment. FSIS would also use a new estimate of just over one million 

Salmonella illnesses annually [40]. This results in a new estimate of 1,080 illnesses with a lower limit of 130 and 

an upper limit of 3,000. 

24 
Siluriformes fish data summary 29 March 2022 

An alternative attribution model can be constructed using information from IFSAC.2 IFSAC estimates that about 

1.5% (0.7% lower bound, 2.6% upper bound) of the approximately one million annual Salmonella illnesses 

come from fish. Because there is no current attribution of Salmonella illnesses from Siluriformes fish, we use 

consumption data to help develop one. The National Health and Nutrition Examination Survey (NHANES) 

consumption data shows that about 6% of fin fish servings that are consumed in the United States are 

Siluriformes fish (Appendix C). Multiplying 1.5% by 6% by the 1,027,561 illnesses estimated by Scallan (2011) 

gives an estimate of 930 illnesses attributable to Siluriformes fish with a lower bound of 270 and an upper 

bound of 2,600. No adjustment is made for different cooking methods for Siluriformes fish compared to other 

types of fish (Appendix C). 

It should not be surprising that these two estimates are so close to each other because both are based on the 

same set of reported outbreaks. Nevertheless, the 2015 risk assessment used the one outbreak attributable to 

Siluriformes fish in 1991 and the alternative model uses the IFSAC estimates with the assumption that all fish 

contribute equally to illness. 

Salmonella Sampling for Siluriformes Fish Compared to Other Commodities 

As noted in Table 39, there were 1,259 Salmonella samples from Siluriformes fish in FY 2020. Of these, 607 

were from domestic samples (Table 40) and 652 were from imported samples (Table 41). The higher of the two 

estimates of the annual Salmonella illnesses in the United States is 1,080. Thus, for each sample taken there 

are 0.9 illnesses. 

We can compare this to other categories of FSIS-inspected products by taking the number of illnesses 

estimated by using the IFSAC attribution fraction and dividing them by the number of samples reported by FSIS 

for other categories. The results are shown in Table 42. 

Table 42. Estimated illnesses for different products subject to FSIS inspection compared to number of samples taken for FY 2020 

Food category Attribution fraction Illnesses Samples Illnesses/sample 

Beef 6.40% 65,764 17,328 3.8 

Chicken 14.00% 143,859 25,942 5.5 

Pork 10.30% 105,839 7,422 14.3 

Turkey 6.20% 63,709 3,231 19.7 

Siluriformes fish 0.09% 1,080* 1,259 0.9 

Total 380,708 55,182 6.9 

*The larger value of 1080 is used rather than the 930 using the attribution fraction 

Table 42 shows that for each Salmonella sample that FSIS collects, there are about seven estimated Salmonella 

illnesses. Thus, Siluriformes fish would appear to be greatly over-sampled compared to other categories. If we 

limit our analysis to only domestic Siluriformes fish samples, then the illnesses per sample is 1.8, still well 

below the average for other FSIS inspected categories. 

2 Interagency Food Safety Analytics Collaboration. Foodborne illness source attribution estimates for 2017 for Salmonella, Escherichia 

coli O157, Listeria monocytogenes, and Campylobacter using multi-year outbreak surveillance data, United States. Atlanta, Georgia and 

Washington, District of Columbia: U.S. Department of Health and Human Services, CDC, FDA, USDA/FSIS,2019, 

https://www.cdc.gov/foodsafety/ifsac/pdf/P19-2017-report-TriAgency-508-revised.pdf 

25 
Siluriformes fish data summary 29 March 2022 

Conclusions 

FSIS residue testing appears to be having a measurable effect. For example, at the beginning of the program 

over 7% of samples tested positive for dyes. That value fell to less than 1%. Other veterinary drugs were 

verified to have detection rates below 1%. For contaminants such as pesticides and metals, a disproportionate 

number of positive tests come from wild-caught Siluriformes fish, where their exposure cannot be controlled. 

Nevertheless, less than 1% of tests were positive for pesticides. Of the metals detected, most positive tests 

were for metals that are not of toxicological concern. For metals that would be of concern, tested samples had 

levels that were either below EPA limits or below values set by other countries for their imports. 

With regards to Salmonella, FSIS testing indicates that domestic Siluriformes fish have an average of 3.53 

percent positive from FY 2016 to FY 2020. Imported Siluriformes fish have an average 0.32 percent positive 

from FY 2016 to FY 2020. This difference may be attributed to imported Siluriformes fish typically being frozen, 

whereas domestic Siluriformes fish are typically fresh. While Salmonella is present on Siluriformes fish, there is 

limited data to support Siluriformes fish attribution to any Salmonella illnesses or outbreaks, except for an 

outbreak identified 30 years ago. Most Siluriformes fish are consumed fully cooked, which could explain the 

limited number of illnesses and outbreaks associated with this product. Based on consumer cooking practices, 

lack of recent outbreaks attributed to Siluriformes fish, and low percent positives detected, FSIS concludes that 

Salmonella does not pose a significant health hazard in Siluriformes fish. Presently, for the number of 

estimated Salmonella illnesses attributed to Siluriformes fish, FSIS is over-sampling Siluriformes fish compared 

to other products. Changes in consumer cooking practices or in the processing environment (to where 

Siluriformes fish have a higher Salmonella percent positive) may alter the public health significance. 

Recommendations 

The following recommendations are made with the intent to better understand the risk posed by possible 

Siluriformes fish contaminants: 

1. Develop a research priority for examining the effect of freezing on recovery of Salmonella from 

Siluriformes fish using FSIS methods. Different studies using different animal products yield different 

results. Knowing the log10 reduction expected from freezing would allow FSIS to better evaluate results 

from imported frozen Siluriformes fish. 

2. Consider suspending current FSIS Salmonella sampling in Siluriformes fish based on the updated illness 

estimates from the attribution-based risk assessment, the low overall occurrence of Salmonella in FSIS 

Siluriformes fish sampling results, and the absence of outbreaks attributable to Siluriformes fish. 

3. Conduct further analysis (speciation) of positive arsenic samples to verify the presence of organic 

arsenic rather than inorganic arsenic. This would increase confidence in the safety of FSIS inspected 

product. 

26 
Siluriformes fish data summary 29 March 2022 

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tumor promoter. Toxicol Lett, 1995. 81(2-3): p. 107-13. 

27 
 

Siluriformes fish data summary 29 March 2022 

24. Morris, J.E., et al., The carcinogenic activity of some 5-nitrofuran derivatives in the rat. Cancer Res, 

1969. 29(12): p. 2145-56. 

25. Zoroddu, M.A., et al., The essential metals for humans: a brief overview. J Inorg Biochem, 2019. 195: p. 

120-129. 

26. Valković, V., Is aluminum an essential element for life? Orig Life, 1980. 10(3): p. 301-5. 

27. Lewis, D.H., Boron: the essential element for vascular plants that never was. New Phytol, 2019. 221(4): 

p. 1685-1690. 

28. Linder, M.C. and C.A. Goode, Biochemistry of copper. Biochemistry of the elements. 1991, New York: 

Plenum Press. xiv, 525 p. 

29. Monsen, E.R., Dietary reference intakes for the antioxidant nutrients: vitamin C, vitamin E, selenium, 

and carotenoids. J Am Diet Assoc, 2000. 100(6): p. 637-40. 

30. Saper, R.B. and R. Rash, Zinc: an essential micronutrient. Am Fam Physician, 2009. 79(9): p. 768-72. 

31. Lewis, J., et al., Stability of arsenic speciation in fish muscle samples, under different storage and 

sample preparation conditions. Microchemical Journal, 2012. 105: p. 56-59. 

32. Agency for Toxic Substances and Disease Registry, Toxicological Profile for Arsenic. 2007. p. 

https://www.atsdr.cdc.gov/ToxProfiles/tp2.pdf. 

33. Agency for Toxic Substances and Disease Registry, Toxicological Profile for Nickel. 2016. p. 

https://www.atsdr.cdc.gov/toxprofiles/tp15.pdf. 

34. U.S. Environmental Protection Agency, Office of Research and Development, Office of Health and 

Environmental Assessment, Environmental Criteria and Assessment Office, Health Assessment 

Document for Nickel and Nickel Compounds. 1986. p. 

https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=30001ACC.PDF. 

35. WHO, Chromium in drinking Water, in Guidelines for drinking-water quality. 2003, World Health 

Organization. 

36. DiGirolamo, R., J. Liston, and J.R. Matches, Survival of virus in chilled, frozen, and processed oysters. 

Appl Microbiol, 1970. 20(1): p. 58-63. 

37. Dominguez, S.A. and D.W. Schaffner, Survival of salmonella in processed chicken products during frozen 

storage. J Food Prot, 2009. 72(10): p. 2088-92. 

38. Dykes, G.A., S.M. Moorhead, and S.L. Roberts, Survival of Escherichia coli O157:H7 and Salmonella on 

chill-stored vacuum or carbon dioxide packaged primal beef cuts. Int J Food Microbiol, 2001. 64(3): p. 

401-5. 

39. Mead, P.S., et al., Food-related illness and death in the United States. Emerging infectious diseases, 

1999. 5(5): p. 607-625. 

40. Scallan, E., et al., Foodborne illness acquired in the United States--major pathogens. Emerg Infect Dis, 

2011. 17(1): p. 7-15. 

28 
Siluriformes fish data summary 29 March 2022 

Appendix A: List of screened veterinary drug residues 

2 Amino Flubendazole Eprinomectin Prednisone 

2 Aminosulfone Albendazole Erythromycin Propionylpromazine 

2 Quinoxalinecarboxylic Acid Fenbendazole Ractopamine 

Abamectin Fenbendazole sulfone Ronidazole 

Acepromazine Fenbendazole sulphone Salbutamol 

Albendazole Florfenicol Salinomycin 

Amikacin Florfenicol Amine Sarafloxacin 

Amoxicillin Flubendazole Selamectin 

Ampicillin Flunixin Spectinomycin 

Apramycin Gamithromycin Streptomycin 

Azaperone Gentamycin Sulfate Sulfachlorpyridazine 

Butorphanol Haloperidol Sulfadiazine 

Carazolol Hydroxydimetridazole Sulfadimethoxine 

Carbadox Hydroxyipronidazole Sulfadoxine 

Cefazolin Hydroxymetronidazole Sulfaethoxypyridazine 

Chloramphenicol Hygromycin Sulfamerazine 

Chlorpromazine Ipronidazole Sulfamethazine 

Chlorpropham Ivermectin Sulfamethizole 

Chlortetracycline Kanamycin Sulfamethoxazole 

Cimaterol Ketamine Sulfamethoxypyridazine 

Ciprofloxacin Ketoprofen Sulfanilamide 

Clenbuterol Lasalocid Sulfanitran 

Clindamycin Levamisole Sulfapyridine 

Clothianidin Lincomycin Sulfaquinoxaline 

Cloxacillin Melengestrol Acetate Sulfathiazole 

Cypermethrin Meloxicam Sulfisoxazole 

Danofloxacin Metronidazole Taleranol 

Deltamethrin Monensin Tetracycline 

Desacetyl Cephapirin Morantel tartrate Tildipirosin 

Desethylene Ciprofloxacin Moxidectin Tilmicosin 

Desfuroylceftiofur Nafcillin Tolfenamic 

Diclofenac Narasin Tolfenamic Acid 

Dicloxacillin Neomycin Triflupromazine 

Difloxacin Norfloxacin Tulathromycin 

Dihydro Streptomycin Orbifloxacin Tylosin 

Dimetridazole Oxacillin Tylvalosin 

Dipyrone Oxyphenylbutazone Virginiamycin 

Doramectin Oxytetracycline Xylazine 

Doxycycline Penicillin Zearalanol 

Emamectin Phenylbutazone Zeranol 

Enrofloxacin Pirlimycin Zilpaterol 

29 
Siluriformes fish data summary 29 March 2022 

Appendix B: List of screened pesticides 

Acephate Ethion Norflurazuron 

Acetamiprid Ethofumesate Omethoate 

Alachlor Fenoxaprop ethyl P,P-DDE 

Aldicarb Fenpropathrin Pentachloroaniline 

Aldrin Fenvalerate Pentachlorobenzene 

Atrazine and Metabolites Fipronil Permethrin Cis and Trans 

Azinphos methyl Fipronil desulfinyl Piperonyl_Butoxide 

Azoxystrobin Fipronil sulfide Pirimiphos methyl 

Benoxacor Fluridone Prallethrin 

Bifenthrin Fluroxypyr-1-Methylhepyl Ester Profenofos 

Boscalid Fluvalinate Promethazine 

Buprofezin HCB Propachlor 

Carbaryl Heptachlor and metabolites Propanil 

Carbofuran and 3-hydroxycarbofur Hexachlorobenzene Propetamphos 

Carfentrazone Ethyl Hexazinone Propiconazole 

Chlordane Hexythiazox Propyzamide Pronamide 

Chlordane Cis and Trans Imazalil Pyraclostrobin 

Chloroneb Imidacloprid Pyridaben 

Chlorothalonil Indoxacarb Pyriproxyfen 

Chlorpyrifos Lindane Resmethrin 

Chlorpyrifos Methyl Linuron Simazine 

Coumaphos and Oxygen Analog Malathion Sulprofos 

Cyhalothrin Metalaxyl Tebufenozide 

DDT and Metabolites Methamidophos Tefluthrin 

Diazinon Methomyl Tetrachlorvinphos 

Dichlorvos Methoxyfenozide Tetraconazole 

Dieldrin Metolachlor Thiabendazole 

Difenoconazole Metribuzin Thiamethoxam 

Diflubenzuron MGK 264 Thiobencarb 

Dimethoate Myclobutanil Trifloxystrobin 

Diuron Natural_Pyrethrins 

Endosulfan I, II, and Sulfate Nonachlor Trans 

30 
Siluriformes fish data summary 29 March 2022 

Appendix C: Determining proportion of Siluriformes fish servings 

Consumer dietary data for all finned fish was extracted from NHANES3 . Different types of fish and different 

methods of preparation were identified by individual food codes. These 140 different codes gave an estimate 

of 7.4 billion servings annually. Catfish accounted for 10 codes and about 450 million servings, or about 6% of 

all finned fish servings. 

We thus start with an assumption that, in the absence of specific attribution evidence, of all Salmonella 

illnesses from fish, about 6% would be attributable to catfish. This would certainly be reasonable if catfish 

were prepared the same as other fish. We find, however, that catfish preparation differs from other fish. 

Possible preparation methods from NHANES included raw, unspecified cooking, canned, dried, pickled, 

smoked, steamed, baked or broiled, fried, or unspecified preparation at a fast-food establishment or 

restaurant. For servings that were baked or broiled the fish could be coated or uncoated. Fried servings were 

always coated. 

Catfish were twice as likely to be coated and fried as other fish. 

Percent of fish servings coated or fried 

Preparation Catfish All other fish Total 

Coated, baked or broiled 35,845,010 450,040,470 485,885,480 

Coated, fried 159,011,020 1,031,953,553 1,190,964,573 

Not coated, baked or broiled 200,436,273 2,679,533,534 2,879,969,807 

Total baked or broiled or fried 395,292,303 4,161,527,558 4,556,819,860 

% fried 40.2% 24.8% 26.1% 

% coated 49.3% 35.6% 36.8% 

Total servings 447,247,485 6,963,821,666 7,411,069,151 

% fried 35.6% 14.8% 16.1% 

% coated 43.6% 21.3% 22.6% 

Does this make catfish less likely to cause illness? The 2015 risk assessment developed a cooking model that 

concluded baking resulted in a median 7 log10 reduction of Salmonella. Frying on the other hand, resulted in 

only a median 4.5 log10 reduction. Thus, the larger percent of catfish that are fried means that catfish would be 

more likely to cause illness than other finned fish and there is no need to adjust illness estimates down. 

3 Centers for Disease Control and Prevention (CDC). National Center for Health Statistics (NCHS). National Health and 

Nutrition Examination Survey Data. Hyattsville, MD: U.S. Department of Health and Human Services, 

Centers for Disease Control and Prevention, 2017-2018, 

https://wwwn.cdc.gov/nchs/nhanes/search/datapage.aspx?Component=Dietary&CycleBeginYear=2017 

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Siluriformes fish data summary 29 March 2022 

List of food codes used 

26100100 Fish, NS as to type, raw 26131120 Pompano, baked or broiled, fat added 

26100110 Fish, NS as to type, cooked, NS as to cooking method 26131121 Pompano, baked or broiled, no added fat 

26100120 Fish, NS as to type, baked or broiled, made with oil 26131131 Pompano, coated, baked or broiled, no added fat 

26100123 Fish, NS as to type, baked or broiled, no added fat 26131140 Pompano, coated, fried 

26100130 Fish, NS as to type, coated, baked or broiled, made with 26131160 Pompano, steamed or poached 

oil 

26100133 Fish, NS as to type, coated, baked or broiled, no added 26133110 Porgy, cooked, NS as to cooking method 

fat 

26100140 Fish, NS as to type, coated, fried, made with oil 26133120 Porgy, baked or broiled, fat added 

26100160 Fish, NS as to type, steamed 26133121 Porgy, baked or broiled, no added fat 

26100170 Fish, NS as to type, dried 26133130 Porgy, coated, baked or broiled, fat added 

26100200 Fish, NS as to type, from fast food 26133140 Porgy, coated, fried 

26100260 Fish stick, patty or nugget from fast food 26133160 Porgy, steamed or poached 

26100270 Fish stick, patty or nugget from restaurant, home, or 26137100 Salmon, raw 

other place 

26101110 Anchovy, cooked, NS as to cooking method 26137110 Salmon, cooked, NS as to cooking method 

26101180 Anchovy, canned 26137120 Salmon, baked or broiled, made with oil 

26105140 Carp, coated, fried 26137121 Salmon, baked or broiled, made with butter 

26107110 Catfish, cooked, NS as to cooking method 26137122 Salmon, baked or broiled, made with margarine 

26107120 Catfish, baked or broiled, made with oil 26137123 Salmon, baked or broiled, no added fat 

26107121 Catfish, baked or broiled, made with butter 26137124 Salmon, baked or broiled, made with cooking spray 

26107123 Catfish, baked or broiled, no added fat 26137130 Salmon, coated, baked or broiled, made with oil 

26107130 Catfish, coated, baked or broiled, made with oil 26137131 Salmon, coated, baked or broiled, made with butter 

26107131 Catfish, coated, baked or broiled, made with butter 26137133 Salmon, coated, baked or broiled, no added fat 

26107140 Catfish, coated, fried, made with oil 26137140 Salmon, coated, fried, made with oil 

26107143 Catfish, coated, fried, no added fat 26137141 Salmon, coated, fried, made with butter 

26107144 Catfish, coated, fried, made with cooking spray 26137142 Salmon, coated, fried, made with margarine 

26107160 Catfish, steamed or poached 26137160 Salmon, steamed or poached 

26109110 Cod, cooked, NS as to cooking method 26137180 Salmon, canned 

26109120 Cod, baked or broiled, made with oil 26137190 Salmon, smoked 

26109121 Cod, baked or broiled, made with butter 26139110 Sardines, cooked 

26109122 Cod, baked or broiled, made with margarine 26139180 Sardines, canned in oil 

26109123 Cod, baked or broiled, no added fat 26139190 Sardines, skinless, boneless, packed in water 

26109130 Cod, coated, baked or broiled, made with oil 26141110 Sea bass, cooked, NS as to cooking method 

26109133 Cod, coated, baked or broiled, no added fat 26141120 Sea bass, baked or broiled, fat added 

26109140 Cod, coated, fried, made with oil 26141130 Sea bass, coated, baked or broiled, fat added 

26109141 Cod, coated, fried, made with butter 26141140 Sea bass, coated, fried 

26109160 Cod, steamed or poached 26141160 Sea bass, steamed or poached 

26109180 Cod, dried, salted, salt removed in water 26143120 Shark, baked or broiled, fat added 

26111120 Croaker, baked or broiled, fat added 26151110 Trout, cooked, NS as to cooking method 

26111140 Croaker, coated, fried 26151120 Trout, baked or broiled, made with oil 

26113110 Eel, cooked, NS as to cooking method 26151121 Trout, baked or broiled, made with butter 

26115120 Flounder, baked or broiled, made with oil 26151130 Trout, coated, baked or broiled, made with oil 

26115121 Flounder, baked or broiled, made with butter 26151133 Trout, coated, baked or broiled, no added fat 

26115123 Flounder, baked or broiled, no added fat 26151140 Trout, coated, fried, made with oil 

26115130 Flounder, coated, baked or broiled, made with oil 26151160 Trout, steamed or poached 

26115140 Flounder, coated, fried, made with oil 26151190 Trout, smoked 

26115160 Flounder, steamed or poached 26153100 Tuna, fresh, raw 

26117120 Haddock, baked or broiled, fat added 26153120 Tuna, fresh, baked or broiled, fat added 

26117121 Haddock, baked or broiled, no added fat 26153122 Tuna, fresh, baked or broiled, no added fat 

26117130 Haddock, coated, baked or broiled, fat added 26153131 Tuna, fresh, coated, baked or broiled, no added fat 

26117140 Haddock, coated, fried 26153160 Tuna, fresh, steamed or poached 

26118020 Halibut, baked or broiled, made with oil 26153170 Tuna, fresh, dried 

26118030 Halibut, coated, baked or broiled, made with oil 26155110 Tuna, canned, NS as to oil or water pack 

26118050 Halibut, steamed or poached 26155180 Tuna, canned, oil pack 

26119110 Herring, cooked, NS as to cooking method 26157110 Whiting, cooked, NS as to cooking method 

26119120 Herring, baked or broiled, fat added 26157120 Whiting, baked or broiled, made with oil 

26119140 Herring, coated, fried 26157123 Whiting, baked or broiled, no added fat 

32 
Siluriformes fish data summary 29 March 2022 

26121110 Mackerel, cooked, NS as to cooking method 26157132 Whiting, coated, baked or broiled, made with 

margarine 

26121120 Mackerel, baked or broiled, fat added 26157140 Whiting, coated, fried, made with oil 

26121121 Mackerel, baked or broiled, no added fat 26157160 Whiting, steamed or poached 

26121140 Mackerel, coated, fried 26158000 Tilapia, cooked, NS as to cooking method 

26121160 Mackerel, pickled 26158010 Tilapia, baked or broiled, made with oil 

26121180 Mackerel, canned 26158011 Tilapia, baked or broiled, made with butter 

26123121 Mullet, baked or broiled, no added fat 26158012 Tilapia, baked or broiled, made with margarine 

26125120 Ocean perch, baked or broiled, fat added 26158013 Tilapia, baked or broiled, no added fat 

26127110 Perch, cooked, NS as to cooking method 26158014 Tilapia, baked or broiled, made with cooking spray 

26127120 Perch, baked or broiled, made with oil 26158020 Tilapia, coated, baked or broiled, made with oil 

26127121 Perch, baked or broiled, made with butter 26158021 Tilapia, coated, baked or broiled, made with butter 

26127130 Perch, coated, baked or broiled, made with oil 26158023 Tilapia, coated, baked or broiled, no added fat 

26127140 Perch, coated, fried, made with oil 26158024 Tilapia, coated, baked or broiled, made with cooking 

spray 

26127143 Perch, coated, fried, no added fat 26158030 Tilapia, coated, fried, made with oil 

26127160 Perch, steamed or poached 26158050 Tilapia, steamed or poached 

33