Bullfrog Antibiotic Exceedance Tops Trending Searches: What Hidden Risks Lie Behind 'One Set for Testing, Another for Sale'? How Can Food Safety Testing Find a Way Out?

On August 3, multiple topics about "bullfrog antibiotic exceedance" successively topped the trending searches on social platforms, triggering strong public concern over the safety of aquatic food.

According to a joint investigation by The Paper (Pengpai News) and the public-interest organization "Zirantian", multiple batches of bullfrogs sold through e-commerce and offline channels were found to contain antibiotics exceeding the limits, with the highest exceeding by more than 5 times, and some samples even testing positive for furazolidone, a veterinary drug explicitly banned by the state. Even more concerning, the investigation exposed the industry hidden rule of "sending antibiotic-free samples for testing while actually selling routinely over-limit bullfrogs".

At present, market regulators in multiple localities, including Chenghai District of Shantou, Guangdong, and Dongshan County of Zhangzhou, Fujian, have moved quickly to seal the involved enterprises on site, take samples for testing, and open cases for a comprehensive and in-depth investigation.

I. Hidden Risks Behind the Unwritten Rule: Which "Invisible Residues" Are Threatening the Dining Table?

High-density intensive farming in aquaculture is highly prone to disease; some farmers, in order to reduce mortality, use drugs in violation of regulations or fail to strictly observe withdrawal periods, resulting in excessive veterinary drug residues. The health risks of the key drug residues involved in this incident cannot be ignored:

1. Nitrofurans: Furazolidone and Its Metabolite (AOZ) — Banned Veterinary Drug with Extremely High Risk

• Risk level: Highest (detection is explicitly banned by the state)

• Mechanism of harm: Furazolidone is rapidly metabolized in the body into the highly stable 3-amino-2-oxazolidinone (AOZ), which binds tightly to tissue proteins. Ordinary high-temperature cooking cannot break down its structure at all.

• Health toxicity: It is clearly carcinogenic, teratogenic, and mutagenic (the "three-gen" effects) and genotoxic; it can cross the placental barrier and affect fetal development, posing serious and lasting harm to children and long-term consumers.

Furazolidone

2. Quinolones: Enrofloxacin

• Risk level: Restricted use (strict withdrawal period and maximum residue limit (MRL) must be observed)

• Mechanism of harm: A broad-spectrum antibacterial drug for animals. Slaughtering before the withdrawal period elapses leads to excessive residues in the meat.

• Health toxicity: Long-term intake of excessive residues can cause drug accumulation in the human body, induce bacterial resistance, and damage the liver; it may also affect cartilage development in children and fetuses, increasing the risk of joint damage.

Enrofloxacin

3. Amphenicols: Florfenicol

• Risk level: Restricted use (a substitute for chloramphenicol)

• Mechanism of harm & toxicity: Widely used against infections in aquaculture and livestock. Animal studies show it has clear embryo toxicity, and excessive intake poses potential health risks to specific populations.

Florfenicol

II. The Bottom-Line Basis for Testing: These National Standards Are Key

From farming to the dining table, the compliance determination of every link of the bullfrog must be based on specific national standards. Reviewing the core substances involved in this incident, the currently effective testing bases mainly include:

1. Maximum Residue Limit Standards

• GB 31650-2019 National Food Safety Standard — Maximum Residue Limits for Veterinary Drugs in Food (with the supplementary standard GB 31650.1-2022): specifies that the maximum residue limit for enrofloxacin (calculated as the sum of enrofloxacin and ciprofloxacin) in animal muscle is 100 µg/kg; it also explicitly states that nitrofurans and other substances fall within the category banned for food-producing animals and must not be detected.

• Announcement No. 250 of the Ministry of Agriculture and Rural Affairs — List of Drugs and Other Compounds Prohibited for Use in Food-Producing Animals: Furazolidone and other nitrofurans are included in the banned list, which has been in effect since its release in December 2019.

2. Testing Method Standards

• GB 31656.3-2025 Determination of Ciprofloxacin, Enrofloxacin, Oxolinic Acid and Flumequine Residues in Aquatic Products by High Performance Liquid Chromatography: replacing the previous GB 31656.3-2021 version, it is the current method standard for detecting enrofloxacin and other substances in aquatic products.

• GB 31656.13-2021 Determination of Multiple Nitrofuran Metabolite Residues in Aquatic Products by Liquid Chromatography-Tandem Mass Spectrometry: specifies the detection methods for four nitrofuran metabolites (AOZ, AMOZ, AHD, SEM) in aquatic products such as fish, sea cucumber and soft-shelled turtle, and in the edible tissues of crustaceans such as shrimp and crab.

• GB/T 20756-2006 Determination of Chloramphenicol, Thiamphenicol and Florfenicol Residues in Edible Animal Muscle, Liver and Aquatic Products by Liquid Chromatography-Tandem Mass Spectrometry: the current testing method standard for florfenicol.

3. Supporting Industry Actions

• In 2024, the China Cuisine Association, together with Haidilao and other enterprises, released the group standard Technical Specification for Bullfrog Farming and Processing, covering the full-chain technical requirements from farming, processing and transportation to testing — a rare bullfrog-specific specification in the industry.

• The Measures for the Administration of Commitment-to-Compliance Certificates for the Quality and Safety of Agricultural Products, effective from February 1, 2026, has brought farmed aquatic products into its management scope, requiring production and procurement entities to issue, collect and retain certificates in accordance with the law.

III. CATO: Empowering Accurate Testing of Veterinary Drug Residues in Aquatic Products

CATO (Guangzhou CATO Technology Co., Ltd.) has long provided reference standards, including those for veterinary drug residue testing, to third-party testing institutions, disease control systems, customs ports, and food and drug testing laboratories. Its product catalog covers the category of "Veterinary Drug Residue Testing Reference Standards", including the key drug categories involved in this incident, such as quinolones, amphenicols, nitrofurans and their metabolites. For example:

Note: The above only shows the core reference standards and isotope-labeled internal standards related to this incident. CATO can provide a complete reference standard library covering veterinary drug residue testing in aquatic products and livestock/poultry (including more antibiotics, illegal additives, and custom mixed-standard services).

If you need to inquire about other veterinary drug residue reference standards, CAS number matching, or request the latest product catalog, please contact CATO directly or visit our official website www.cato-chem.com.