Introduction


Fish is a highly perishable food, and its safety and quality depend on proper handling, storage, temperature control, and the absence of prohibited chemical adulterants.

Concerns about chemicals such as formalin and illegal food colours have raised questions about how consumers can identify chemically treated fish. However, it is important to distinguish between signs of poor freshness and evidence of chemical adulteration.


Formalin and Fish


Formalin is a solution containing formaldehyde.

Formaldehyde is a hazardous chemical and is classified as a human carcinogen. Exposure can irritate the eyes, nose, throat, and respiratory tract, while significant or prolonged exposure may result in more serious health effects.

Formalin is not permitted as a preservative for fresh fish. Its illegal use to artificially maintain the appearance of freshness is therefore a food-safety concern.

However, consumers should not assume that a fish that looks unusually fresh has necessarily been treated with formalin. Visual appearance alone cannot establish the presence of formaldehyde.


What About Illegal Colours?


The illegal use of non-permitted colours is another potential food-safety concern.

Certain industrial dyes, including Rhodamine B, are not permitted for use as food colours.

However, the presence of a bright red or unusually attractive colour in fish does not, by itself, establish that Rhodamine B or any other particular dye has been used.

Fish can naturally vary in colour depending on species, freshness, handling, storage conditions, and other factors.

Therefore, colour alone cannot be used to diagnose chemical adulteration.


Can You Identify Chemically Treated Fish by Looking at It?


Freshness indicators such as:

* Odour
* Eye appearance
* Gill colour
* Flesh firmness
* Overall appearance

can provide useful information about the quality and freshness of fish.

However, these characteristics cannot reliably confirm whether a fish has been treated with formalin, an illegal dye, or another prohibited chemical.

A fish may appear fresh without having been chemically treated, while chemical adulteration may not always be obvious from its appearance.


Why Home Tests Can Be Misleading


There are various home methods promoted online for detecting formalin or other chemicals in food.

The problem is that an unvalidated home test may produce misleading results.

Chemical adulteration should not be confirmed simply by relying on a single visual characteristic, smell, texture, or an unvalidated home testing method.

When chemical adulteration is suspected, appropriate rapid screening methods or laboratory testing should be used for confirmation.


The Importance of Proper Handling and Storage


Fish naturally deteriorates because of microbial activity, enzymatic processes, and other changes after harvest.

Maintaining the cold chain, proper hygiene, appropriate storage, and hygienic handling are therefore essential for maintaining fish quality and safety.

The goal of food preservation should be to maintain safety and quality through appropriate handling and storage, not by using prohibited chemicals to artificially maintain the appearance of freshness.


Conclusion


Formalin is not a permitted preservative for fresh fish, and formaldehyde exposure can pose health hazards. Illegal food colours such as Rhodamine B are also a food-safety concern.

However, you cannot reliably confirm chemical adulteration simply by looking at the fish, checking its colour, smelling it, or judging its firmness.

When adulteration is suspected, appropriate screening or laboratory testing is required for confirmation.

The key message is simple:

Fish should be genuinely fresh, properly handled, appropriately stored, and free from prohibited chemical adulterants—not merely made to look fresh.


References


Issue of Formalin in Fish – FSSAI.

Guidance Note on Formalin in Fish – FSSAI.

Malachite Green and Leucomalachite Green in Fish – U.S. FDA.

Rhodamine B – FSSAI.