How to Identify Fish Containing Formalin: 5 Warning Signs to Know
Fresh-looking fish may not always be safe to eat. Learn the warning signs, understand the health risks and find out how to choose fish more safely.
For many Bangladeshi families, fish is an essential part of everyday meals. But choosing fresh fish at the market can sometimes be challenging. Concerns about the misuse of chemicals to preserve fish during transportation and storage have made consumers more cautious.
Formalin, a solution containing formaldehyde, is widely known for its preservative properties. However, formaldehyde is hazardous to human health, and fish suspected of chemical contamination should be handled carefully. Importantly, you cannot reliably confirm the presence of formalin simply by looking at, touching or smelling fish. Laboratory testing is needed for confirmation.
Health Risks of Formalin Exposure
Formaldehyde exposure can cause adverse health effects, depending on the amount, route and duration of exposure. Potential effects include:
- Respiratory irritation: Exposure may irritate the nose, throat and airways.
- Allergic reactions: Some people may experience irritation or sensitivity.
- Digestive problems: Ingestion can cause irritation of the digestive tract, nausea and other symptoms.
- Potential organ damage: Significant exposure can have serious health consequences.
- Cancer risk: Formaldehyde is classified as carcinogenic to humans, particularly based on evidence concerning certain types of cancer associated with exposure.
The actual risk from eating fish depends on the level of contamination and the amount consumed. Not every fish that looks unusually fresh or has a strong smell contains formalin.
5 Possible Warning Signs When Buying Fish
Certain characteristics can help you assess fish freshness. However, none of these signs alone can establish whether formalin has been used.
1. Check Whether Flies Are Present
Some buyers believe that flies avoid fish treated with formalin because of its strong odour. However, the presence or absence of flies is not a reliable test for detecting formalin. Flies may be absent for several reasons, including the market environment and the way fish is displayed.
2. Examine the Texture of the Flesh
Fresh fish generally has firm flesh that springs back when gently pressed. Flesh that is unusually soft, mushy or easily damaged may indicate spoilage.
However, firm or rubbery flesh does not prove that formalin has been used. Fish species, temperature and storage conditions can all affect texture.
3. Pay Attention to the Smell
Fresh fish usually has a mild, clean, sea-like or characteristic fishy smell. A strong sour, rancid, ammonia-like or chemical odour should raise concern.
Avoid buying fish with an unusual chemical smell, but remember that smell alone cannot confirm formalin contamination.
4. Inspect the Gills and Eyes
Fresh fish typically has clear, bright eyes and moist, reddish or pinkish gills, depending on the species and condition.
Dull or sunken eyes, brownish gills, excessive mucus and an unpleasant smell may indicate that the fish is no longer fresh. Bright red gills alone do not mean the fish contains formalin.
5. Look at the Scales and Overall Appearance
Fresh fish generally has scales that are firmly attached, skin that appears moist and flesh that retains its natural shape.
Loose scales, damaged skin, discolouration or a deteriorating appearance may indicate poor handling or spoilage. Nevertheless, visual inspection cannot determine whether a chemical preservative has been added.
How to Reduce the Risk of Chemical Contamination
If you suspect that fish has been treated with formalin, washing or cooking should not be considered a guaranteed way to make it safe.
Here are some practical precautions:
- Buy from a trusted seller: Choose vendors who maintain proper hygiene and keep fish appropriately chilled.
- Keep fish cold: Refrigerate fresh fish promptly and avoid leaving it at room temperature for extended periods.
- Wash and handle carefully: Rinse fish under clean running water before preparation and keep raw fish separate from ready-to-eat foods. Washing helps remove surface dirt but does not guarantee the removal of formaldehyde.
- Cook thoroughly: Proper cooking reduces many biological hazards, but it cannot be relied upon to eliminate chemical contamination.
- Avoid suspicious products: If fish has an unusual chemical odour or other concerning characteristics, do not taste it or attempt to make it safe through repeated washing.
- Report suspected adulteration: Contact the relevant food safety or consumer protection authorities if you suspect that a seller is using prohibited chemicals.
Can Formalin Be Removed by Washing Fish?
Formaldehyde is soluble in water, but the extent to which washing reduces residues depends on several factors, including the concentration, exposure conditions and how deeply the chemical has penetrated the fish.
There is no universally reliable home method—whether soaking in warm water, washing for a particular number of minutes or cooking at high temperatures—that guarantees the removal of formalin to a safe level.
For this reason, prevention is more dependable than trying to remove a suspected contaminant after purchase.
Final Word
Buying fresh fish requires more than simply checking its colour, smell or texture. Although these observations can help assess freshness, they cannot reliably distinguish chemically treated fish from untreated fish.
The safest approach is to buy fish from reputable sellers, maintain proper refrigeration and avoid fish suspected of chemical contamination. When formalin use is suspected, laboratory testing—not guesswork—is the reliable way to establish its presence.
