Hazardous chemical contaminants found in fishes

Ch Basudha / Arati Ningombam / L Kanta Singh / Anand Wakambam *

Fish is among the healthiest foods on the planet, and contains important nutrients, a good source of easily digestible proteins. Fish is rich in vitamins A and D. Fish is also a great source of omega-3 fatty acids, which are incredibly important for your body and brain. This includes high-quality protein, iodine, and various vitamins and minerals.

Fish makes an important contribution to an overall healthy diet by providing protein, fatty acids, and certain vitamins and minerals Substantial dietary intake of LC n-3 polyunsaturated fatty acids can be obtained readily by eating fatty fish or larger amounts of lean fish. Therefore, individuals who eat no fish will have difficulties in meeting the daily intakes of LC n-3 PUFA recommended for cardiovascular health and foetal development.

However, fish can also contribute significantly to dietary exposure to contaminants such as methyl mercury, dioxins and PCBs, brominated flame retardants, and organotin compounds. Concentrations of these contaminants in fish vary with the nature of the contaminant and the type of fish. Fat-soluble contaminants (such as dioxins and dioxin-like compounds) are especially found in fatty fish.

In contrast, methyl mercury levels are not related to the fat content of the fish but due to its accumulation in the food chain, methyl mercury is present in higher amounts in large predatory fish. Hence, the present paper discusses fish feed used in Manipur and its effect on health.

Fish as a Food in Manipur

Manipuri cuisine, cultural beliefs and traditions, in particular, surrounding elements of traditional Manipuri medicine; and most importantly, notions of social status and conspicuous consumption linked to the development of the state economy and social stratification. Live fishes viz. Wallago attu, carps, catfishes, varieties of loaches, and various small indigenous are premium fishes and are in the top list of ready market.

Huge quantities of dried either smoked or salted sun dried fish are also in the list of consumer demand and market. These processed fish items are brought from other states like Gujarat, Andhra Pradesh, Assam, Bihar, Uttar Pradesh, and the coastal states of India.

Fermented item, Ngari has become an irreplaceable and inseparable ingredient of almost all Manipuri dishes such as Kangsoi, Iromba, Ametpa, Singju etc. As the state fish production could not meet the consumers’ demand, the fish were brought from other states. Huge quantities of dried and smoked fish are also imported from Myanmar through Moreh, Manipur.

Harmful Heavy Metals and Chemicals Found in Fish

Fish can be available easily and considered a super food; rich in omega fatty acids, protein, and low-density lipoprotein are key factors for human health. Fish can provide the necessary nutrition for health. However, increasing urban spaces, agricultural activities, use of chemicals, pollution of ecosystems, industrialization, oil spills, and overfishing are affecting the aquaculture sector negatively.

Harmful chemicals that enter the environment through waste emissions and chemical spills can contaminate soil, air and water both directly and indirectly. Besides, pesticides, industrial effluents, and heavy metals are also a major nuisance leading to the deterioration of aquaculture mainly in developing economies such as India. Fish can absorb these chemicals from food and water; and people are exposed to these harmful chemicals when they eat contaminated fish.

Fish are very sensitive to water pollution and bioaccumulation due to direct contact with water. Heavy metal contamination of water not only affects the health of fish negatively but also the people who consume the fish. The Federation of Indian Animal Protection Organisations (FIAPO) and All Creatures Great and Small (ACGS) conducted a study about 250 fish and shrimp farms across the highest-producing states in India.

It comprises both freshwater and brackish water fish farms in Andhra Pradesh Tamil Nadu, Pondicherry, Gujarat, West Bengal, and Orissa, and freshwater farms in Bihar, Jharkhand, Chattisgarh, and Assam. It has been found that hazardous levels of metals such as lead and cadmium are in all of them (The Hindu, 2021).

Reckless uses of antibiotics and insecticides for the cultivation of fish has a potential threat of antimicrobial resistance and it has contributed to making aquaculture a “ticking time bomb,” according to the author. Heavy metal and metalloid pollution of farmland and crops can substantially impact food safety as well as human health.

Formaldehyde and Chemical Preservatives Found in Fishes

There are reports on using formalin, toxic and carcinogenic chemicals commonly used to preserve fish and thereby preventing them from deteriorating during transportation. Derivatives of free formaldehyde were detected in carps by many workforces. In the rural area of India, the average consumption of carp (Labeo rohita (Rohu) and Catla catla (Katla)) is higher than that of other types of fish.

The published report revealed that imported rohu contains 3 to 4-fold higher formalin concentration than rohu freshly harvested from ponds although formaldehyde is known to be toxic to living tissues and has been reported to be responsible for numerous complex human diseases, it is used as a preservative to extend the shelf life of fish, due to its low cost.

Though dry fish is very popular in the state, consumption is hazardous to human health as the preservative used to keep the fish dry is highly toxic. Sodium benzoate is commonly used as a food preservative because of its ability to inhibit bacterial and fungal growth. A solution of sodium benzoate is acidic, which makes it effective at killing microorganisms, which are unable to survive in acidic environments.

Sodium benzoate and ammonia were found in the samples that slow down the melting of ice and are used to preserve fish for a longer time.

Though fish either dried or fresh brought from other states is a popular delicacy across the state, its consumption may be hazardous to human health as the preservative used to keep the fish either fresh or dry for longer keeping quality is highly toxic. The public should be enlightened on the inherent danger that may accompany consumption of contaminated fish and fishery products.


Fish is one of the staple food items for the people of Manipur. Hence, one should have protected farms and ponds from toxic chemicals. Fish ponds should maintain good water quality from good water sources, healthy fish seeds, proper stocking density, good feed and feeding practices, and good post-harvest techniques.

In general, fish and fishery products have a good safety record and a large proportion of food-borne diseases associated with fish are due to a lack of good hygienic and good handling practices after fish are harvested. However, during harvest, fish become contaminated by contact with sick workers or water, ice, hands, harvesting equipment, and containers that are not cleaned properly.

Therefore, consumers should be aware of the health risks of eating unsafe fish and should demand that all fish products are required to include catch documentation and traceability information. Consumers should look for fish products that are certified as being sustainably and responsibly produced and tracked along their supply chain.

People should buy only high-quality fish (i.e., fresh fish, clear eyes and shiny, fresh, and red gills with no odour, fish should smell fresh, not fishy or ammonia-like, firm flesh, etc).

Submitted by
ICAR Research Complex
for NEH Region,
Manipur Centre,

* Ch Basudha / Arati Ningombam / L Kanta Singh / Anand Wakambam wrote this article for The Sangai Express
This article was webcasted on 01 February 2023

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