According to FDA Import Refusal data and Import Alerts, the following, among other substances, have been found in imported fish from Vietnam and China:

• Malachite green: This is, according to Wikipedia, “a toxic chemical primarily used as a dye. When diluted, it can be used as a topical antiseptic or to treat parasites, fungal infections, and bacterial infections in fish and fish eggs. It is also used as a bacteriological stain.

“However, in 1992 in Canada, it was determined that there is a significant health risk to humans who eat fish contaminated with malachite green. The chemical was classified a Class II Health Hazard because it was found to be toxic to human cells and might cause liver tumor formation. However, due to its ease and low cost to manufacture, it is still used in certain countries with less restrictive laws for non-aquaculture purposes.”

• Crystal violet, or gentian violet: This is a bactericide and an antifungal agent used by hospitals for the treatment of serious heat burns and other injuries to the skin and gums.

According to Wikipedia, “one study has linked long term exposure to large amounts of Gentian violet with cancer. The FDA has determined that gentian violet has not been shown by adequate scientific data to be safe for use in animal feed. Use of gentian violet in animal feed causes the feed to be adulterated and is a violation of the Federal Food, Drug, and Cosmetic Act. On June 28, 2007, the FDA issued an ‘import alert’ on farm-raised seafood from China because unapproved antimicrobials, including gentian violet, had been consistently found in the products.”

• Chloramphenicol: a bacteriostatic antimicrobial. The drug is considered a prototypical broad-spectrum antibiotic, alongside the tetracyclines. It can cause a leukemia called aplastic anemia.

• Fluoroquinolone antibiotics: A family of synthetic broad-spectrum antibiotics, “the first generation (of fluoroquinolones) was derived from an attempt to create a synthetic form of chloroquine, which was used to treat malaria during World War II,” according to Wikipedia. “Resistance to quinolones can evolve rapidly, even during a course of treatment. Numerous pathogens … now exhibit resistance worldwide. Though considered to be a very important and necessary drugs required to treat severe and life threatening bacterial infections, the associated antibiotic misuse remains unchecked, which has contributed to the problem of bacterial resistance. The overuse of antibiotics … has given rise to a breed of super bacteria which are resistant to antibiotics entirely.”