Pao Baileyi Pufferfish Care Sheet
- Macauley Sykes
- Apr 10, 2020
- 20 min read
Updated: Oct 20
This care sheet is written with the aim of providing the optimal care for this species of fish.
Pufferfish Enthusiasts Worldwide endeavours to inspire and promote the highest standards of care - not basic or minimum care - using the best evidence available at the time
Introduction
The Pao baileyi is one of the most striking and recognisable members of the freshwater puffer family. Endemic to the Mekong River Basin, it is found in Thailand, Laos, and Cambodia, where it lives among the rocks and crevices of the river’s middle and lower reaches.
In these clear, moving waters, it hides in plain sight, its mottled body blending seamlessly with the stones around it.
This fish is best known to aquarists as the 'Hairy Puffer', a name earned from the tiny filaments that cover its skin. These fine cirri are small extensions of the outer layer, breaking up the outline of the fish and helping it vanish against rock and gravel. When viewed in the wild, it can look almost like part of the riverbed itself, a living piece of camouflage that comes to life only when food passes close enough.
The species was first described by Suebsin Sontirat in 1985. Its scientific name honours Professor Dr Reeve M. Bailey, a well-respected American ichthyologist, who served as Professor of Biological Sciences and Curator of Fishes at the Museum of Zoology.
Like many Asian freshwater puffers, Pao baileyi has a complex taxonomic history. It was initially placed in Monotrete, a now-defunct genus once used for several riverine species across Southeast Asia, and was later moved to Tetraodon, which historically served as a catch-all category for most pufferfish worldwide.
Continued study showed that these classifications grouped species that were only superficially alike and not truly close relatives.
A major revision by Maurice Kottelat in 2013 finally resolved these relationships. His review of Southeast Asian inland fishes re-established Pao as a valid genus for the region’s true freshwater puffers, separating them from their brackish and marine counterparts.
Since that clarification, Pao has been firmly recognised in ichthyological literature as a natural freshwater lineage within the family Tetraodontidae. Each member shows the same quiet intelligence and deliberate behaviour that make these fish so compelling in captivity, but Pao baileyi stands apart through its extraordinary camouflage and almost sculptural stillness. It is a puffer built to disappear, its beauty revealed only when it chooses to move.
Adult specimens typically reach around 12 to 15 centimetres in length. They are not large fish, but they have an unmistakable presence. Those who keep them often describe a sense of awareness in the way they observe the world. When secure, they will follow movement outside the tank, rest in open view, and occasionally adjust their position with a slow, careful motion that seems almost thoughtful.
For many years, every Pao baileyi in the aquarium trade was wild-caught. The species was regarded as almost impossible to breed in captivity, with only scattered, anecdotal reports suggesting otherwise. That view began to shift in 2024, when the Natural History Bulletin of the Siam Society published a peer-reviewed account of successful captive spawning and fry development. Since then, a handful of experienced aquarists and small commercial breeders have reported similar outcomes.
Even so, most P. baileyi entering the trade today still originate from the wild. Captive-bred examples remain uncommon but mark an encouraging step toward sustainability in the keeping of this remarkable species.
In the Wild
Pao baileyi comes from the middle and lower stretches of the Mekong River, with confirmed records from Thailand, Laos, and Cambodia. The species was first described from a specimen collected in the Boondharik District of Ubon Ratchathani Province, northeastern Thailand, and remains common in that region. Additional museum records exist from Khong Chiam in Ubon Ratchathani and from Luang Prabang Province in Laos.
Further vouchered and sequenced specimens confirm its range along the Mekong mainstem into northeastern Cambodia. Reports from Vietnam have appeared in older literature but remain unverified.
The Mekong in this region is one of the most dynamic river systems on Earth. It rises and falls dramatically with the monsoon, reshaping its channels every season. During the dry months, the current tightens through rocky narrows, exposing boulders and deepening pools. When the rains return, the same ground floods beneath several metres of fast, oxygen-rich water. Pao baileyi inhabits this shifting boundary between high flow and calm margin, selecting the stable pockets and ledges that persist through both extremes.
Collectors describe the fish resting close to the substrate among rocks, gravel, and submerged roots, avoiding open water but never far from the flow. It holds position in gaps and hollows between stones, emerging only to feed or to move to a new vantage point. At rest, it appears lifeless, its body pressed against the rock and its cirri moving with the current like short fronds of algae. From above, it is almost invisible.
The fish probably occupies depths of one to four metres, favouring shaded zones where the current runs cleanly over the bottom. The substrate in these areas is mixed: coarse sand, rounded gravel, and smooth stone, often coated with a thin layer of algae and biofilm. These surfaces host a rich community of invertebrates, including freshwater shrimps, crabs, snails, and insect larvae, all forming the base of the puffer’s food web.
Field surveys from the Lower Mekong Basin record water conditions typical of this environment. The pH lies between 6.3 and 8.0, most often close to neutral. Conductivity ranges from 90 to 150 µS/cm, and total hardness is usually below 100 mg/L as CaCO₃, describing water that is soft to moderately hard and rich in oxygen. Temperature remains warm throughout the year, from 23 to 29 °C, with only slight cooling during the height of the rains.
Although little is known about its seasonal movement, Pao baileyi almost certainly follows the rise and fall of the river. During floods, it may shift into quieter margins and flooded forest edges where prey is more abundant. As waters recede, it returns to the deeper, oxygenated pools of the main channel.
Within these habitats, it lives alongside loaches (Schistura, Nemacheilus), small catfish (Glyptothorax, Pseudolaguvia), and other benthic fish adapted to similar conditions. Its stillness and camouflage allow it to remain unseen until the moment it strikes.
Diet in the Wild
There are no formal gut-content studies for Pao baileyi, so its diet must be pieced together from field observation, habitat records, and what is known of its close relatives. In both form and behaviour, it is a patient ambush predator.
In the Mekong, Pao baileyi lives among rocks and coarse sand, where it lies motionless between stones or settles half-buried in the substrate. It waits for movement within reach, striking with sudden precision. Collectors working in the river describe how the fish holds its position in small crevices, lunging forward when a shrimp, crab, or small fish passes by. Small benthic cyprinids and other shoaling species often move through the same shallow runs, and Pao baileyi is well equipped to seize any that wander too close.
Its diet likely contains many of the animals that share those rocky margins: freshwater shrimps such as Macrobrachium and Caridina, small gecarcinucid crabs including Esanthelphusa and Parathelphusa, benthic molluscs from families Thiaridae and Viviparidae, and insect larvae from Chironomidae, Odonata, and Ephemeroptera. All are abundant across the Lower Mekong and perfectly suited to a predator that relies on stealth and short bursts of power.
Seasonal changes in the river likely shape its feeding habits. During the flood season, when the water spreads through vegetated margins, softer crustaceans and insect larvae become abundant. As levels fall and current strengthens, the fish probably relies more on snails, worms, and other benthic prey that remain in the main channel.
Chemical analyses of other freshwater Pao species from the Mekong have detected saxitoxins (STX) rather than tetrodotoxin (TTX), suggesting a dietary link through the food web. The toxin likely originates in cyanobacteria consumed by snails and crustaceans, which are then eaten by the puffer. Although Pao baileyi has not been tested directly, it probably follows the same pathway.
Taken together, these clues describe Pao baileyi as a quiet, deliberate hunter that feeds mainly on the small crustaceans, molluscs, and insect larvae of the riverbed, occasionally taking small fish when opportunity allows.
Conservation Status
The IUCN Red List currently lists Pao baileyi as a species of Least Concern, based on an assessment published in 2011. At that time, populations were considered stable across the Mekong Basin, and no specific threats were recorded as causing a significant decline. Since then, however, the Mekong has undergone considerable changes.
Across the Lower Mekong, hydropower construction, damming, sand extraction, and channel modification have altered flow regimes and sediment dynamics on an unprecedented scale. The rocky, oxygen-rich zones that Pao baileyi depends on are gradually being eroded, buried, or flooded under impoundments. Fine sand and gravel beds are being removed faster than they can replenish, reducing the structural variety that supports many benthic fish.
The species remains locally common in undisturbed stretches of the river, but its long-term security is uncertain. The very qualities that define its habitat (clarity, current, and complex stonework) are among those most easily lost to development.
Until the IUCN reassesses Pao baileyi under current conditions, its official listing will remain “Least Concern,” but its effective conservation status in the field is far less secure. Protecting the physical and chemical integrity of the Mekong is essential if this remarkable fish, so precisely adapted to its environment, is to continue thriving in the years ahead.
In the Aquarium
The Hairy Puffer has long been a favourite among keepers of ambush puffers. Most of those found in the aquarium trade are still wild-caught from the Mekong River system, although captive-bred fish have now begun to appear following recent breeding successes. Whether wild or tank-bred, Pao baileyi adapts readily when its environment reflects the structure and rhythm of the waters that shaped it.
In nature, Pao baileyi inhabits rocky sections of the Mekong and its larger tributaries, often in areas of moderate to strong current. It lives pressed tight against the landscape, wedged between stones or beneath ledges where the flow is broken but the water remains highly oxygenated. The aquarium should mirror that world: constant movement, stability, and places of shelter within the current.
Flow should be firm and continuous but never violent. A large canister filter or sump provides the turnover and oxygenation required. Angle spray bars across the surface to maintain gas exchange, and ensure that circulation reaches every layer of the tank. Many keepers add a small, guarded powerhead to prevent dead spots, but all intakes must be fitted with protective covers. This species regularly squeezes into narrow spaces, and an exposed grill can easily trap or injure it.
Aquascaping should focus on structure and function rather than ornamentation. Use smooth boulders, driftwood, and solid rockwork to create interlocking pockets and shaded crevices where the fish can brace its body and rest. Between these, leave open areas of soft, fine sand to allow for wallowing. A sand bed matching the fish’s body depth lets it settle naturally, sinking until only the eyes and cirri remain visible.
Plants are optional but can soften the layout and provide extra harbourage, which is beneficial to the fish. Hardy epiphytes such as Anubias and Microsorum pteropus (Java fern) work well attached to rock or wood. Avoid rooted species, as the puffer’s digging behaviour soon dislodges them.
Pao baileyi produces a heavy biological load for its size, so robust filtration and frequent large water changes are essential. The species thrives in clean, highly oxygenated water with stable parameters and minimal nitrate buildup.
When these needs are met, the aquarium takes on the quiet rhythm of the Mekong itself. Flow ripples gently across the surface, light moves on stone, and the fish sits wedged between rocks, watching. Then, with no warning, it strikes: precise, powerful, and composed. In that moment, the Hairy Puffer reveals exactly what it is: a river predator perfectly adapted to stillness, current, and control.
Substrate
In the wild, Pao baileyi spends much of its time half-hidden among stones and sand, waiting for the slightest movement that might signal a potential meal. It is an ambush predator that relies on patience and camouflage rather than pursuit. In the aquarium, this behaviour remains exactly the same. A relaxed specimen will often bury itself up to the eyes or wedge into a shallow pocket between rocks, staying perfectly still until it decides to move.
Fine sand is not optional. It is essential.
This species is a true wallower and must be given a soft substrate that allows it to bury naturally without risk of abrasion. A smooth, fine sand replicates the texture of the riverbed and gives the fish confidence to rest in the open without injury or stress.
Recommended substrate details:
Ideal choice: fine, sugar-soft sand
Grain size: 0.2–0.5 mm (very fine, smooth texture)
Best types: aquarium-grade fine sand, well-rinsed play sand, or smooth pool-filter sand that is chemically inert and free from sharp grains
Avoid: gravel, plant soils, or coarse sands. Even rounded gravels stop proper wallowing and can injure the fish when it tries to bury itself
To maintain the sand correctly, aim for a natural bed that supports good circulation and prevents compaction:
Keep the sand bed around 2–5 cm deep in most areas, adding a little more in the puffer’s favourite wallowing sites
Stir or rake small sections during weekly water changes to release trapped gases and maintain oxygen exchange
Maintain strong surface flow so debris does not settle and collect in dead spots
When siphoning, vacuum lightly across the top rather than disturbing the lower layers
A soft sand substrate is not decorative but functional. It forms part of the fish’s environment and behaviour. Without it, Pao baileyi cannot settle or display its calm, watchful nature. With it, the puffer behaves as it does in the river: patient, confident, and perfectly at home.
Tank size
In nature, Pao baileyi leads a quiet, settled life among rocks and sand. It stays close to the bottom, shifting between crevices and shaded pockets rather than venturing into open water. This behaviour continues in captivity, where the fish prefers to rest or wallow for much of the day.
It is not a strong swimmer, but it does need room to feel secure and to explore its surroundings at its own pace.
An aquarium measuring at least 80 cm in length and 35–40 cm from front to back, with a height of about 40 cm, provides a comfortable base for a single adult. This gives roughly 110–120 litres of water volume, enough to hold a stable environment with space for sand, rockwork, and areas of open ground. A tank of this size also supports consistent filtration and makes it easier to maintain clean, well-oxygenated water.
Larger aquariums are always an advantage. Extra space allows for stronger flow without creating stress, helps spread waste more evenly, and gives the keeper freedom to design a more natural scape with plenty of structure. When Pao baileyi has space to claim its own territory, it behaves with quiet confidence, sitting out in the open and observing what happens around it.
Water values
Maintain the following water parameters:
PH: 6.5-7.8 (in the middle is ideal)
Temperature: 24-26°C (75 -78.8°F)
Ammonia (NH₃/NH₄⁺): 0 ppm
Nitrite (NO₂⁻): 0 ppm
Nitrate (NO₃⁻): Below 15 ppm (ideal)
General Hardness (GH): 3–10 °dGH
Why these Numbers?
These recommendations reflect the conditions recorded within the Mekong River Basin, where Pao baileyi inhabits clear, oxygen-rich waters over sand, stone, and submerged roots. Field surveys from Thailand, Laos, and Cambodia describe moderately flowing sections of the main river and its tributaries with neutral to slightly alkaline chemistry and low to moderate mineral content. Conductivity in these habitats typically falls between 90 and 150 μS/cm, equating to roughly 3–8 °dGH.
Temperature across the Lower Mekong remains warm throughout the year, averaging 24–29 °C with only minor seasonal variation. The recommended aquarium range of 24–28 °C sits comfortably within this band, reflecting the stability of its native environment. Within this range, the fish’s metabolic rate remains balanced: warm enough to promote healthy appetite, smooth digestion, and active observation, yet cool enough to maintain strong oxygen availability. Cooler conditions slow feeding response and reduce alertness, while prolonged heat above 29 °C increases metabolic demand and can lead to oxygen stress.
A pH of 6.5–7.8 mirrors the stable, lightly buffered waters of the Lower Mekong. These rivers run clear but carry enough carbonate hardness to prevent abrupt chemical shifts. Mid-range values around 7.0 tend to produce steady behaviour and consistent feeding response.
Ammonia and nitrite should always remain at 0 ppm, as all puffers are acutely sensitive to nitrogenous waste. Even small traces can cause gill irritation and rapid distress.
Nitrate should be kept low, ideally below 15 ppm, as a sign of clean, well-managed water rather than a precise toxicity threshold. High nitrate levels indicate organic build-up and tend to suppress the fish’s natural confidence and colour.
Tankmates
Pao baileyi is a solitary species by nature. In the wild, it keeps to itself, holding a small territory among stones and roots where it hunts alone. It does not form groups or share space with others of its kind. This instinct carries through in captivity, where it views any other fish as either competition or food.
Because of this, Pao baileyi should always be kept alone. Small tankmates will be eaten sooner or later, and larger or faster species cause constant stress by intruding on their territory. Even other puffers cannot be trusted together once they mature, as territorial disputes are common and often fatal.
A single puffer in its own aquarium is the best and most natural arrangement. When left undisturbed, Pao baileyi settles quickly, feeds well, and becomes confident enough to sit in the open or watch activity outside the tank. In solitude, it shows its full character — calm, aware, and perfectly at ease.
Sexual dimorphism
Although a captive-breeding trial in 2024 documented both male and female Pao baileyi spawning and raising fry, no definitive external sexual dimorphism has been described.
There are no reliable visual differences between male and female Pao baileyi. Scientific descriptions and field studies make no mention of external traits that can be used to distinguish the sexes, and the species is generally regarded as sexually monomorphic.
The small variations sometimes reported by aquarists, such as males having more cirri or slightly slimmer bodies, are anecdotal and unverified. Accurate sexing of this species requires internal examination or genetic testing, neither of which is practical or ethical for routine aquarium keeping. In all normal circumstances, the fish should be regarded as not externally sexable.
Notable behaviour
In captivity, Pao baileyi behaves much as it does in the wild. It spends long periods wedged between hardscape, equipment, or tank walls, watching everything that moves.
These tight spaces provide security and a clear vantage point from which to observe its surroundings. It rarely swims in open water except to feed or investigate changes in its territory.
P. baileyi is highly territorial and can become defensive toward the keeper. It will lunge at objects that enter its space, and its bite can cause serious injury. Maintenance should always be carried out with an awareness of the fish’s position.
A confident Hairy Puffer is steady and observant. It may sit exposed on the substrate or rest between rocks, calmly following movement outside the glass.
Feeding
Feeding Pao baileyi reveals a kind of controlled brutality. It watches, waits, and then explodes into motion with startling speed. The jaws clamp shut with an audible snap, and the prey is crushed and cut in an instant. A few slow bites follow, the fragments chewed deliberately before being swallowed. It is over as quickly as it began.
A settled P. baileyi will feed in full view once it learns the rhythm of its keeper. It may follow movement across the glass, then return to its chosen spot to wait. When the tongs appear, it focuses completely. There is no hesitation, only the calm certainty of a predator that knows what to do. Feeding should never be treated as a spectacle; it is an expression of instinct, and it deserves quiet observation.
Although formal gut analyses are lacking, field studies and ecological overlap with related species make its diet clear. Pao baileyi is a benthic feeder, consuming freshwater crustaceans, worms, snails, and other invertebrates that live among rock and sand.
Recommended Foods:
Freshwater snails of varying sizes (pond, ramshorn, and similar species)
Fresh or frozen crab and/or crayfish from freshwater sources
Gut-loaded earthworms
Gut-loaded cockroaches, crickets, and locusts
Thiaminase-free fish fillet or small fish pieces, offered occasionally for variety
Occasional small aquatic insects
Feed once daily or every other day, depending on appetite and temperature. Offer food using feeding tongs, holding it still until the fish strikes. P. baileyi often hits with surprising force, so calm, deliberate handling is important. Remove uneaten food immediately to maintain water quality.
Marine-derived foods such as prawns, mussels, and clams should not be used as staples. They differ nutritionally from the freshwater prey this species has evolved to digest and are often high in thiaminase, which can cause long-term deficiency.
Suggested Feeding Breakdown
The following proportions reflect the natural balance and long-term observation in captivity:
30% Freshwater crustaceans (crab and crayfish)
20% Freshwater snails and other molluscs
30% Worms and insect larvae
15% Thiaminase-free fish and soft protein
5% Enrichment foods
These ratios provide a practical framework for feeding while ensuring that hard-shelled prey are offered regularly for dental maintenance and that soft foods form a varied and digestible staple.
Feeding Fish
Pieces of fish can be offered occasionally to add variety to the diet of Pao baileyi, but they should never form a major part of its feeding routine. In the wild, this species feeds mainly on crustaceans, worms, and other bottom-dwelling invertebrates. Small fish may be taken opportunistically, but they do not represent a significant part of its natural diet. The aim in captivity is to preserve that same balance.
When offering fish, always choose thiaminase-free species. Thiaminase breaks down vitamin B₁ (thiamine), and long-term exposure can cause deficiency, neurological issues, and appetite loss.
Recommended Thiaminase-Free Species
Tilapia (Oreochromis spp.)
Trout (Oncorhynchus mykiss)
Cod (Gadus morhua)
Pollock (Pollachius spp.)
Haddock (Melanogrammus aeglefinus)
Catfish (Ictalurus or Pangasius)
Pike or Perch, when cleanly sourced from freshwater
Fish to Avoid
Avoid goldfish, minnows, anchovies, sardines, herrings, and most smelts. These are thiaminase-positive and unsuitable for long-term feeding.
Preparation
Because most market fish are too large to feed whole, prepare small, clean portions:
Remove the head, fins, and internal organs.
Fillet the fish, leaving scales and skin intact.
Cut into small, manageable pieces that the puffer can swallow easily.
Freeze for at least seven days to eliminate parasites.
Thaw gently in cool water before feeding.
Offer fish flesh no more than once every one to two weeks, alternating with the invertebrate-based foods that form the bulk of the diet.
Always feed by tong to control portion size and prevent uneaten food from spoiling the substrate.
Because Pao baileyi digests soft protein slowly, large or frequent portions of fish can lead to poor water quality and internal fat buildup. Used sparingly and prepared correctly, however, small pieces of clean fish can provide a useful variety without disrupting digestion or behaviour.
Feeder fish
Using live feeder fish might seem like a simple solution when a new Pao baileyi refuses food, but it almost always creates more problems than it solves. Feeder fish are typically raised in crowded, unsanitary conditions and are one of the most common sources of disease in home aquariums. They often carry parasites such as Ichthyophthirius multifiliis (Ich), Trichodina, Gyrodactylus, Dactylogyrus, and Camallanus worms. Many also harbour bacterial infections like Flavobacterium columnare (Columnaris). Introducing them into your tank can undo months of careful quarantining and health progression in a single feeding.
Even when parasites are avoided, live feeders can cause deeper behavioural issues. Pao baileyi is a sharp and deliberate hunter. Once it learns to associate food with movement, it can become fixated on live prey and reluctant to accept anything else. This often leads to long periods of fasting or stubborn refusal to eat prepared foods, frustrating both fish and keeper.
A safer and far more effective approach is to start with fresh or frozen foods from the beginning. Thiaminase-free fish fillets, small pieces of prawn, mussel, or freshwater crab, along with gut-loaded worms and snails, all provide excellent nutrition without risk. These foods also allow full control over cleanliness and portion size.
Once tong training begins, most Hairy Puffers quickly adapt to non-living foods and feed with confidence. Live feeders add nothing of real value to their care. They are unnecessary, unpredictable, and almost always more harmful than helpful.
Tong Training
Tong training is one of the most valuable habits a keeper can develop with Pao baileyi. It does far more than make feeding easier. Each session helps build familiarity and trust between fish and keeper, turning mealtime into a calm, shared routine rather than a chase. Over time, the Hairy Puffer begins to recognise its keeper’s movements and waits at the glass in anticipation of being fed.
One of the greatest advantages of tong training is its impact on diet and nutrition.
By feeding directly from the tongs, the fish learns to associate the tool with safety and food, which makes it far more willing to try new items. This gradual familiarity allows the keeper to introduce a wider range of foods, ensuring balanced nutrition and preventing dietary monotony.
Filtration & Tank Maintenance
Although Pao baileyi is not an active swimmer, it produces a surprising amount of waste for a single fish. In a closed aquarium, the waste accumulates quickly. Without strong biological filtration and a consistent routine, the water can degrade long before it appears unclean.
For most setups, a large external canister filter is the best choice. Its combination of high biological capacity and fine mechanical filtration keeps the water both clear and stable. In larger aquariums, a sump system adds further reliability. It increases total water volume, enhances gas exchange, and provides space to hide heaters, media, and other equipment away from view, keeping the display natural and uncluttered.
No filter, however efficient, can replace a consistent maintenance routine.
Pao baileyi is a messy eater, often scattering fragments of food around the tank, and uneaten material quickly spoils the water. We strongly recommend vacuuming debris from the substrate at every water change, paying close attention to areas beneath rocks and driftwood where waste tends to collect.
Clean, stable water is the foundation of success:
Keep nitrate below 15 ppm, as close to 0ppm as possible
Change at least 50% of the water weekly, increasing frequency during periods of heavier feeding.
Lightly vacuum the sand surface at each change, especially around rocks and driftwood where debris tends to collect.
Maintain good surface agitation to ensure high oxygen levels, particularly in warm conditions.
A mature filtration system combined with consistent upkeep provides the same clarity and movement that define the Hairy Puffer’s natural habitat. In these conditions, Pao baileyi remains calm and alert, displaying the quiet confidence and subtle colouration that mark a fish completely at ease in its environment.
Why Keep Nitrates Low?
Like other riverine puffers, Pao baileyi has evolved in clear, oxygen-rich water where continuous current flushes organic matter downstream, keeping dissolved waste near zero. There is no accumulation of waste in such an environment.
In the aquarium, that natural renewal has to come from the keeper through regular, substantial water changes and disciplined feeding.
Chronic nitrate exposure in freshwater fish has been linked to:
Depressed immune response, leaving fish more prone to bacterial and parasitic infections
Reduced appetite and slower growth, often leading to weight loss or dull colouration
Organ stress and shortened lifespan, particularly in species from naturally clean habitats
Aim to keep nitrate below 15 ppm, ideally less. Achieving that target through large weekly water changes and a mature biological filter will ensure that Pao baileyi remains healthy and displays the calm, steady temperament that defines it.
Inflation
Like all pufferfish, Pao baileyi is capable of inflating its body when threatened. This unique defensive response is a last resort, used only when the fish feels cornered or physically restrained. In the wild, inflation helps deter predators by making the puffer appear larger, rounder, and harder to swallow.
In captivity, this behaviour should never be encouraged. Forcing a puffer to inflate for photographs or demonstration causes severe stress and can be harmful. During inflation, the fish rapidly gulps water into a stretchable section of its stomach, expanding the body far beyond its normal shape.
If this occurs in the air, the fish may accidentally take in air instead of water, which can lead to internal injury, buoyancy problems, or even death if the air cannot be expelled.
Occasionally, a relaxed P. baileyi may perform what aquarists call “practice puffing.”
This is a brief, gentle inflation that occurs without a clear reason, usually while the fish is resting. It deflates naturally a few seconds later. These short exercises are harmless and appear to help maintain the flexibility of the skin and muscles used for inflation.
A settled Hairy Puffer seldom inflates at all. In a calm, clean, and stable aquarium, the need for this extraordinary defence almost disappears, showing that the fish feels secure and at ease in its surroundings.
Toxicity and Toxin Origin
There are no published studies which confirm the presence of any toxin in Pao baileyi. To date, the species has not been chemically analysed in any of the toxicological surveys that have examined Mekong or Chao Phraya pufferfish.
However, several closely related species from the same region, including Pao turgidus and Pao suvattii, have been shown to carry paralytic shellfish toxins (PSTs), primarily saxitoxin (STX) and decarbamoyl-saxitoxin (dcSTX). These compounds are completely distinct from tetrodotoxin (TTX), the toxin found in most marine puffers.
Because P. baileyi shares both habitat and diet with these species, it is reasonable to assume that it could acquire the same compounds through the same food-web pathway. In affected species, these toxins are not produced internally but accumulate through diet. They originate from cyanobacteria and other microorganisms that generate PSTs, which pass upward through small crustaceans, molluscs, and other benthic prey before reaching the puffer.
For aquarists, this information is primarily of scientific interest rather than practical concern. In captivity, the cyanobacteria and prey species responsible for saxitoxin production are absent, and prepared foods contain no toxin precursors.
As with all puffers, the only realistic danger is through ingestion, not contact.
Routine maintenance, feeding, or tank interaction poses no risk whatsoever.
Disclaimer
The health and husbandry information provided in this guide is intended for educational purposes only. It should not be taken as or replace the advice of a qualified aquatic veterinarian.
If your pufferfish shows signs of illness or is experiencing a medical emergency, seek assistance from an experienced aquatic veterinary professional without delay.
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