Scientists have confirmed India’s first case of pufferfish poisoning, drawing attention to a largely unrecognised riverine health risk.
Freshwater pufferfish, Tetraodon cutcutia (currently classified as Leiodon cutcutia), contain tetrodotoxin (TTX), a potent neurotoxin found in major river basins including the Ganga, Brahmaputra and Mahanadi.
Studies from the Mahanadi River reveal dense and diverse microbial communities in pufferfish gut and skin.
Pufferfish are often sold unintentionally in mixed freshwater catches, with consumers unaware of the toxin or safe handling practices.
India lacks freshwater fish toxin surveillance and integrated risk assessment, widening the public awareness gap.
In early reports confirmed by Indian scientists, a 23-year-old man from Veraval, Gujarat presented with sudden numbness, vomiting and rapidly progressing paralysis shortly after consuming a low-cost freshwater fish purchased from a village market. Within hours, the patient displayed symptoms consistent with tetrodotoxin exposure, highlighting a health threat that has remained almost entirely invisible in India’s riverine communities. The incident marks the country’s first scientifically verified case of pufferfish poisoning and has drawn renewed attention to this risk.
Pufferfish belong to the order Tetraodontiformes and are known locally by names such as toadfish, patkafish, balloonfish and fugu. Global catalogues list approximately 190–193 valid species. Indian waters currently support eight genera and 32 species of pufferfish. Their distribution is specific to certain regions and river systems, primarily the Western Ghats and major basins such as the Ganga, Brahmaputra and Mahanadi.
Pufferfish are omnivorous and benthic in habitat. Freshwater pufferfish species reported from India are often endemic to specific geographical areas and serve as indicators of healthy river ecosystems. The dwarf pufferfish is classified as Vulnerable on the International Union for Conservation of Nature’s Red List due to declining populations caused by wastewater pollution and collection for the aquarium trade.
What makes these otherwise delicate fish so dangerous is tetrodotoxin (TTX), one of the most potent neurotoxins known in nature. TTX consists of an oxygenated 2,4-dioxaadamantane core and a guanidinium group. It is heat-stable, water-soluble, and a non-protein quinazoline derivative. TTX blocks sodium channels in nerve cells, disrupting electrical signalling and triggering a cascade of symptoms including tingling, numbness, vomiting, falling blood pressure, rapid heart rate, muscular paralysis and respiratory failure.
Across Asia, pufferfish poisoning is widely documented, with deaths reported in Bangladesh, Singapore and Hong Kong. In Japan, where pufferfish (fugu) is consumed as a delicacy, only licensed chefs are permitted to prepare it. India, however, lacks comparable protective measures.
The origin of tetrodotoxin remains an area of scientific debate. A growing body of evidence suggests that pufferfish do not synthesise the toxin themselves. Instead, TTX is believed to originate from symbiotic or ingested bacteria such as Vibrio, Pseudomonas, Aeromonas and Bacillus, which have been isolated from the ovaries, liver and intestinal tissues where toxin concentrations are highest. In India, systematic research on toxin-producing microbial communities associated with freshwater pufferfish remains extremely limited, making this a critical area for future investigation.
Recent studies have described the influence of trophic level on bacterial community composition and functional attributes in the gut microbiota of freshwater pufferfish from the Mahanadi River. Species richness of culturable bacteria in the pufferfish gut from the Mahanadi has been documented, indicating that the gut harbours a wide range of microbiota and derives nutrients from both carbohydrate-rich plant material and protein-rich animal sources.
Microbial species richness in the skin ecosystem of pufferfish has also revealed several novel species, including Acinetobacter kanungonis, Shewanella cutis, Chryseobacterium indicum, Moraxella tetraodonis, and other representative genera such as Vibrio cholerae, Delftia litopenaei, Acinetobacter baumannii, Bacillus marisflavi, Exiguobacterium indicum, Aeromonas veronii, Serratia rubidaea, Bacillus aryabhattai, Bacillus indicus, Staphylococcus haemolyticus, Acinetobacter junii, Aeromonas enteropelogenes, Bacillus cereus, Acinetobacter variabilis, Chromobacterium alkanivorans and Bacillus altitudinis. These findings substantially expand current knowledge of microbial diversity associated with freshwater pufferfish.
In many riverside communities, pufferfish enter local diets not because they are deliberately sought out, but because fishers often catch them as accidental by-catch. Once deflated, they resemble several small-bodied edible fish and are frequently sold mixed with inexpensive freshwater species. Their soft texture and low price make them appealing to consumers who may neither recognise the fish nor appreciate the risks.
Studies show that consumers overwhelmingly lack awareness of pufferfish toxicity, and many households unknowingly consume them without understanding the potential consequences.
Health workers in rural areas are often unfamiliar with the symptoms of tetrodotoxin poisoning. With no known antidote, effective prevention depends entirely on timely recognition, public awareness and basic regulatory safeguards.
India currently has no freshwater fish toxin surveillance programme. At the same time, responses must avoid demonising pufferfish. These species play important ecological roles in Indian rivers, particularly in controlling macroinvertebrate populations and reflecting habitat quality. The challenge is to balance human safety with ecological integrity, ensuring communities are informed without fostering hostility towards wildlife.
The first confirmed case of pufferfish poisoning in India is more than an isolated incident. It is a warning that ecological change, microbial dynamics and human vulnerability are intersecting in ways that remain poorly understood.
As pressures on freshwater ecosystems intensify, addressing this risk requires informed communities, responsive governance and renewed scientific attention. A deeper understanding of pufferfish–microbe relationships could help safeguard public health while also offering valuable indicators of changing conditions in India’s rivers.
Abhijit Poddar is Associate Professor, Mahatma Gandhi Medical Advanced Research Institute, Sri Balaji Vidyapeeth (Deemed to be University), Pondicherry; Debasis Dash is Director, BRIC-Institute of Life Sciences, Department of Biotechnology; and Subrata K Das is Adjunct Faculty and Former Scientist (Retired) BRIC-Institute of Life Sciences, Department of Biotechnology.
Views expressed are the author’s own and don’t necessarily reflect those of Down To Earth