Tetraodon Miurus Pufferfish Care Sheet

Macauley Sykes
Nov 26, 2024
17 min read

Updated: Oct 2

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 Tetraodon miurus (the Congo Puffer) is a striking and highly unusual freshwater pufferfish from the Congo River Basin in Central Africa. Endemic to this immense and turbulent watershed, it is shaped by rapids, shifting sands, and powerful currents. Its appearance mirrors that environment: a compact, blunt-tailed body built for ambush rather than endurance swimming, and colours ranging from deep blacks and mottled browns to vivid oranges and fiery reds.

Tetraodon miurus was first described in 1902 by the Belgian–British zoologist George Albert Boulenger. The species name miurus derives from the Greek myi- (closed or short) and oura (tail), a reference to its stocky, short-tailed form.

It is most widely known as the Congo Puffer or Potato Puffer, but in the aquarium trade it also appears as “Squarehead Puffer,” “Fang Puffer,” and, in its rarest morphs, “Red Congo” or “Red Potato.”

Reaching 12–15 cm (5–6″), the Congo Puffer is medium-sized. It is far smaller than giants such as Tetraodon mbu, yet still large and imposing enough to make a dramatic statement in the aquarium. With a lifespan that can exceed a decade in captivity, it rewards aquarists who are prepared to meet its demanding needs.

What truly sets the species apart is its behaviour. Unlike many puffers that cruise their surroundings, the Congo Puffer spends much of its life buried in fine sand, waiting with only eyes and snout exposed.

When prey approaches, it erupts from the substrate in a lightning-fast strike, a hunting strategy that has made it one of the most theatrical fish in the hobby.

Although undeniably predatory and unsuitable for community aquaria, the Congo Puffer commands admiration for its intelligence, bold personality, and endlessly variable appearance. For dedicated keepers, few fish offer such a compelling blend of beauty, individuality, and natural spectacle.

In the wild

The Congo Puffer inhabits the main channel of the Congo River Basin, with confirmed records from the Lower Congo near Kinshasa–Brazzaville, extending downstream towards the rapids of Boma and upstream into the Lualaba headwaters.

Unlike relatives that favour floodplains and vegetated margins, Tetraodon miurus is a fish of the main flow. It is most often found in turbulent, oxygen-rich reaches where sandbanks, rocky shelves, and root tangles create pockets of cover within fast current.

Field surveys describe these waters as warm, extremely soft, and consistently well oxygenated. Reported values include temperatures of 26–29 °C, pH levels between 6.1 and 7.3, conductivities typically ranging from 30 to 90 µS cm⁻¹, and dissolved oxygen saturation levels from approximately 48% to over 90%, depending on the site and season.

These conditions shape the broader fish community of the Congo and underpin the adaptations of ambush predators such as miurus, which thrive in restless sand and shifting cover.

The Congo is among the world’s most powerful rivers, and its seasonal flood pulse continually reshapes habitats. Sandbars shift, banks collapse, and shelves of rock and roots are exposed as water levels rise and fall. No study has explicitly tracked T. miurus across these changes, but its reliance on fine sand and structural cover suggests that it exploits such shifting microhabitats. Aquarist reports of colour morphs blending with pale or dark substrates are consistent with this idea, although they remain anecdotal rather than formally documented.

Field observations describe individuals lying half-buried in sand or wedged among roots and rocks, their outlines broken and almost invisible against the riverbed. With only eyes and snout exposed, they may remain motionless for hours, relying on camouflage and patience as water and prey drift past. When unsuspecting prey comes within range, the puffer erupts from concealment in a lightning-fast strike and delivers a powerful bite.

Wild-caught specimens and field records indicate a strong reliance on small fishes, making miurus among the most piscivorous of freshwater puffers. It remains opportunistic and will also consume crabs, worms, aquatic insects, and snails when available. Its fused dental plates enable it to dispatch both soft-bodied and hard-shelled prey with ease. In essence, this is a predator of movement, tuned to react the instant something strays too close.

Understanding the Congo Puffer in its natural setting, a world of fast currents, shifting sandbanks, and a prey base dominated by small fishes, explains both its highly specialised needs in captivity and its enduring fascination for aquarists. It is a predator perfectly adapted to one of the most dynamic freshwater systems on Earth.

Conservation

The International Union for Conservation of Nature (IUCN) currently lists Tetraodon miurus as Least Concern. Populations remain healthy in habitats where fast-flowing, oxygen-rich water persists.

However, like all Congo specialists, its fate is tied to the stability of the river itself. Deforestation, urban runoff, and industrial discharge threaten water quality in parts of the basin, while overfishing can reduce the small fishes and crustaceans that make up its prey base. At present, the species is resilient and widespread, but the long-term health of miurus depends on the protection of the Congo’s turbulent main channel.

In The Aquarium

The Congo Puffer is a favourite among oddball enthusiasts, with wild-caught specimens appearing regularly in the trade.

No confirmed captive breeding programmes exist, so every fish originates from the Congo Basin. To keep one is to bring a former resident of that river into the aquarium, and it will only thrive when its environment echoes the conditions that shaped it.

The stretches of river in which Tetraodon miurus evolved are among the most powerful freshwater environments on Earth. The Lower Congo alone drops more than 270 metres in just 350 kilometres, producing rapids, sandbanks, and turbulent margins where oxygen levels remain high year-round. In captivity, recreate the spirit of this environment: lively circulation, abundant oxygen, open sand for wallowing, and clean, stable water.

Flow is critical. This species is not an endurance swimmer, but it does require brisk, highly oxygenated water to remain healthy and active. Use a large canister filter or a sump for dependable turnover and media capacity, then add circulation via guarded powerheads or returns. Aim for overall turnover of roughly six to ten times the tank volume per hour, with strong surface agitation for gas exchange. Always provide resting zones where the fish can wallow without being buffeted. Fit guards or sponges to intakes so a buried puffer cannot be drawn in.

Design the tank with two goals in mind: enable natural behaviours and make them visible.

Build up the sides and back with smooth boulders or rocks, waterlogged driftwood, and ledges to form secure retreats and crevices for resting and ambush. Leave the foreground and centre as open sand so the puffer can bury in full view of the keeper. Heavy, stable hardscape works best in these high-flow tanks.

The fish will also lodge itself between stones, under wood, or in corners, taking advantage of structure as it would in the Congo’s shifting margins. A successful layout balances cover and complexity with openness, providing both shelter and broad sandy flats where the characteristic ambush behaviour can unfold.

Plants are optional. Many struggle in a miurus tank, but hardy epiphytes such as Java fern (Microsorum pteropus), Anubias, and Bolbitis can be attached to wood or rock to soften the hardscape and add extra cover. Rooted plants rarely succeed, since wallowing and strong flow tend to dislodge them.

Aquascaping for this species should prioritise resilience and functionality over delicacy. Think of the tank as an interactive environment rather than a manicured display.

Like all puffers, T. miurus is intolerant of poor water conditions. It produces significant waste for its size and needs both excellent mechanical filtration for particulates and a mature biological filter for stability. Keep dissolved oxygen high and perform frequent, large water changes. Consistency is key, since sudden shifts in chemistry or temperature can quickly stress this fish.

When these conditions are met, the Congo Puffer becomes one of the most rewarding species in the hobby. Its behaviour, combined with striking morphs and obvious intelligence, makes it not only a predator to be kept, but a spectacle to be experienced.

Substrate

The Congo Puffer is an ambush predator that spends much of its time buried in sand or wedged among the hardscape. In the aquarium, it behaves the same, diving headfirst into the substrate and pushing forward with its tail until only the eyes and snout remain visible.

Because this behaviour is central to its lifestyle, the texture of the substrate is critical. Coarse or sharp material can cause scrapes and abrasions as the fish buries, leaving it vulnerable to bacterial or fungal infection. Fine sand is not optional. It is essential.

Fine sand is not optional. It is essential.

Ideal choice: fine, sugar-soft sand
Grain size: 0.2–0.5 mm (very fine, smooth sands)
Best types: aquarium-grade fine sands, well-rinsed play sand, or smooth pool-filter sand that is chemically inert and free of sharp grains
Avoid: gravel, plant soils, or coarse sands. Even rounded gravels prevent proper wallowing and can injure the fish when it attempts to bury itself

Depth and maintenance

The sand should be at least as deep as the fish’s body depth so the Congo Puffer can bury completely when it chooses. A shallow bed is fine for juveniles, then increase the depth as the fish grows.

These puffers shift wallowing sites frequently, leaving shallow impressions as they move.

Sand beds also trap waste and can compact over time, which may create anaerobic zones. The fish will stir the surface during normal activity, but this is not enough to keep deeper areas healthy.

To maintain the substrate:

Keep the sand bed 2–5 cm deep in most areas, adding more only in favoured wallowing sites.
Stir or rake sections during weekly water changes to release trapped gases and circulate oxygen.
Ensure strong water movement across the surface to prevent detritus from settling.
When siphoning, vacuum lightly over the surface rather than disturbing the bed deeply each time.

For Tetraodon miurus, sand is not an aesthetic choice but a fundamental requirement. Only in a fine, forgiving substrate can this puffer display the full range of natural behaviours that make it such a fascinating ambush predator.

Tank size

For Tetraodon miurus, the footprint of the aquarium matters far more than height. This is a sedentary ambush predator that spends almost all of its time on the bottom, burying in sand or lodging between hardscape. It makes little use of the upper water column.

Minimum footprint for a single adult: 80 × 35 cm (31.5 × 13.8″)

Recommended water depth: about 40 cm (15.7″)

Approximate volume: ~112 litres (30 US gallons)

This size represents a realistic off-the-shelf minimum that can accommodate a single specimen if maintained with excellent filtration and water quality.

However, larger tanks are strongly recommended.

Wider footprints such as 90 × 45 cm (~180 L / 47 gal) or 120 × 45 cm (~240 L / 63 gal) provide significantly more stability, space for multiple wallowing zones, and scope for complex scaping.

A low, broad aquarium with abundant floor area mirrors the habitats of the Congo and allows the fish to display their natural behaviours to the fullest.

When choosing a system, always prioritise length and width over depth. A shallow, expansive tank not only suits the fish’s biology, but also offers the keeper the most rewarding view of its ambush and wallowing behaviour.

Water values

Maintain the following water parameters:

Temperature: 26–28 °C (79–82 °F)
pH: 6.3–7.2 (ideal range 6.6–6.9)
General Hardness (GH): 1–6 dGH (soft)
Ammonia (NH₃/NH₄⁺): 0 ppm
Nitrite (NO₂⁻): 0 ppm
Nitrate (NO₃⁻): <15 ppm (lower is better)

Why these numbers?

The water values recommended here are drawn from published environmental surveys of the Lower Congo River, the natural range of Tetraodon miurus, combined with the conditions that aquarists have found most reliable in the long term.

Measurements taken near Kinshasa, Brazzaville, and further downstream describe a river that is consistently warm, soft, and only lightly mineralised. Mean field readings report temperatures around 27–28 °C, pH close to 6.8, and very low conductivity (20–50 µS cm⁻¹). Oxygen saturation is high year-round, particularly in rapid zones, where turbulence can drive the water close to or even beyond full saturation. These findings demonstrate that the Congo Puffer is adapted to slightly acidic to neutral, oxygen-rich water with minimal dissolved minerals. The suggested aquarium range of 26–28 °C and pH 6.3–7.2 sits comfortably within these observations, while leaving some tolerance for the small day-to-day variations typical in aquaria.

In the wild, the Lower Congo is extremely soft, but recreating those conditions exactly in a closed aquarium can lead to instability. Aiming for GH 1–6 dGH and KH 1–3 dKH provides calcium and magnesium needed for osmoregulation and helps prevent the instability associated with ultra-soft water in closed systems. In practice, this strikes a balance between replicating natural conditions and supporting long-term health.

Zero tolerance for ammonia and nitrite is non-negotiable, as puffers are acutely sensitive to nitrogenous waste.

The target for nitrate (<10–15 ppm) is less about avoiding an immediate toxin and more about maintaining an environment that remains consistently clean. Scientific studies show that even moderate nitrate levels can impair growth and weaken immune responses in freshwater fishes over time, so aiming low is best practice.

Taken together, these values mirror the essence of the Congo River - warm, soft, clean, and turbulent with high oxygen content - while being adapted to the realities of aquarium keeping. They provide the balance between authenticity and practicality that allows T. miurus to thrive in captivity.

Tankmates

The Congo Puffer is a solitary ambush predator and should be treated as such in captivity. It is not a community fish under any circumstances.

In the wild, Tetraodon miurus is highly territorial, using ambush sites and cover as individual hunting grounds. Any tankmates small enough to be swallowed will be eaten, and even larger fish risk being struck when they stray too close. Unlike pursuit predators, miurus relies on sudden attacks, and a single bite can cause fatal injury.

Tetraodon miurus is best maintained as the sole inhabitant of its aquarium. A single fish, given adequate space and a properly designed environment, will display the full range of its remarkable natural behaviours.

Sexual dimorphism

There is currently no reliable method for distinguishing the sexes of Tetraodon miurus in the aquarium. Unlike some puffers that show subtle differences in colour pattern, size, or body shape, males and females of this species appear externally identical.

Scientific descriptions also make no mention of consistent sexual characters, and no proven reports of captive breeding exist to provide further insight. It is therefore assumed that all sexual differences are either internal or only apparent during breeding, which has not been observed in aquaria.

For the home aquarist, this means that sexing is not possible.

All individuals should be regarded as indistinguishable in this respect.

Notable behaviour

This species exhibits colour variation and is widely reported (in care literature and hobbyist observation) to shift its appearance to better blend with its surroundings. Typical colours described include brown, red, orange, black, grey, and marbled tones. Such adaptive colouration likely helps with camouflage, but the degree and speed of change remain largely anecdotal and not fully documented.

Another behaviour to be aware of is the potential for jumping or leaping. At least one keeper report describes a “Congo puffer” escaping its aquarium and landing on the floor. For this reason, keepers often advise using a secure, escape-proof lid to prevent such incidents.

Feeding

One of the greatest joys of keeping the Congo Puffer comes from feeding it. These are not fish that simply take food; they strike, crunch, and engulf prey in a way that turns every meal into a performance. Their sharp beaks and lightning-fast movements are the product of a specialised diet in the wild, and as keepers, we have both the privilege and the responsibility of replicating that as closely as possible.

At Pufferfish Enthusiasts Worldwide, we encourage keepers to think of feeding as enrichment as well as nutrition. A varied diet not only provides the full spectrum of vitamins and minerals for long-term health, but also stimulates natural hunting behaviour. Watching a buried T. miurus erupt from the sand to seize prey is to glimpse its lethality in the wild Congo, right in your home aquarium.

In nature, T. miurus opportunistically consumes freshwater crustaceans and benthic invertebrates such as worms, but it is primarily piscivorous, preying upon a wide range of small fishes that drift too close to its ambush site. It doesn't just eat the muscle, but also the bones, organs, and gut contents. This provides a broad spectrum of nutrition: protein from flesh, calcium and phosphorus from bones, fat-soluble vitamins from organs, and plant-derived compounds from whatever the prey itself had eaten.

In captivity, whole fish prey items are rarely available, so keepers usually offer fillets or prepared pieces of fish. While perfectly acceptable as a protein source, these lack much of the nutritional diversity of a whole prey animal. The most effective way to compensate is by gutloading insects and worms with high-quality greens, algae wafers, and vegetable matter. This approach ensures that when the puffer consumes these invertebrates, it also receives many of the plant-based nutrients it would naturally obtain second-hand from the stomach contents of wild prey.

Our preferred foods for these fish include:

Thiaminase-free fish meat, cut into manageable chunks (see Feeding Fish)
Gutloaded Earthworms (a reliable staple)
Gutloaded Cockroaches, crickets, locusts and woodlice
Repashy - Grub Pie, for variety and micronutrient balance

Avoid cockles, mussels, clams, and oysters. These bivalves are not natural foods for T.miurus and can unbalance the diet. Some of these food items also contain thiaminase, which can cause a deadly vitamin B1 deficiency.

Regular feeding of thiaminase-rich fish leads to chronic deficiency, neurological damage, and eventually death. Always ensure that any fish offered is confirmed thiaminase-free.

Ratios and feeding frequency

A good balance is around 40% fish and 60% invertebrates (worms and insects).

Owing to their sedentary lifestyle, Congo Puffers do not require daily feeding.

Two to three meals per week are usually sufficient to maintain health while avoiding obesity.

Feeding fish

One of the most convenient and widely available options is Frozen Pond Smelt (Hypomesus olidus). These small fish are thiaminase-free and the perfect size for miurus to consume whole. They can usually be found in well-stocked aquatic shops or bait suppliers. Aquarists must be cautious, however: other smelt species, such as Rainbow Smelt (Osmerus mordax), do contain thiaminase and should be avoided.

Beyond smelt, aquarists can make use of larger freshwater fish commonly sold at fish counters and markets.

Excellent thiaminase-free and nutritionally safe choices include:

Tilapia (Oreochromis spp.)
Trout (e.g. Rainbow Trout Oncorhynchus mykiss)
Lake Trout (Salvelinus namaycush)
Cod (Gadus morhua)
Pollock (Pollachius spp.)
Haddock (Melanogrammus aeglefinus)
Catfish (Ictalurus, Pangasius)

Foods to Avoid: goldfish, minnows, anchovies, sardines, herrings, and most smelts are all thiaminase-positive and dangerous for long-term use.

Because they are too large for a Congo Puffer to swallow whole, preparation is essential:

Remove the head, fins, and internal organs.
Fillet the fish, leaving scales and skin intact.
Cut the fillets into chunks small enough for miurus to swallow within one minute.
Freeze prepared pieces for at least 7 days (to kill parasites) and store for up to three months.

Other species, such as Salmon, Halibut, Sole, Snapper, and Perch are also thiaminase-free and can be offered occasionally for variety. Oily species like Salmon should be used sparingly.

Feeder fish

We strongly discourage using live feeder fish for Tetraodon miurus. Live feeders are often bred in dense, stressed environments, which can allow diseases (e.g. Flavobacterium columnare / Columnaris) and parasites to proliferate. Introducing feeder fish into your tank significantly raises the risk of transmitting pathogens to your puffer.

Feeders are also frequently nutritionally limited. Many feeder species (especially goldfish, minnows, and rosy reds) contain high levels of thiaminase.

Moreover, habitual feeding of live prey can encourage finickiness: fish may begin rejecting all but live targets. For these reasons (disease risk, nutritional shortcomings, and behavioural dependency) we urge keepers to begin weaning toward frozen, gutloaded prey as soon as possible.

Fortunately, T. miurus does not require live fish to thrive. In many documented cases, individuals will readily accept frozen-thawed prey shortly after introduction to a new aquarium.

Tong Training

For the Congo Puffer, tong training is not just a convenience. It is the key to long-term dietary success. As an ambush predator, Tetraodon miurus can easily become selective in captivity, which makes it difficult to maintain balanced nutrition.

Teaching the fish to take food directly from feeding tongs transforms feeding, while also acting as a valuable bonding tool that encourages more interactive behaviour with the keeper.

Once conditioned, the puffer no longer evaluates food by appearance. Instead, anything offered on the tongs is recognised as edible. This association allows the keeper to introduce unfamiliar foods, from gutloaded insects to prepared diets, with far less resistance.

Over time, the fish will strike confidently at whatever is presented, making it far easier to maintain dietary variety and balance.

Tong training also provides precision and control. Food can be placed exactly where the puffer will take it, reducing waste, keeping the substrate cleaner, and ensuring portion sizes are carefully managed. For a solitary, sedentary predator like T. miurus, tong training adds enrichment as well as safety. It gives the keeper a secure and reliable way to feed a fish with such a powerful bite.

Click here to read our full Tong Training guide.

Filtration and Tank Maintenance

Although the Congo Puffer is a solitary species, it still produces a substantial amount of waste relative to its size. For long-term success, the aquarium must be supported by robust, reliable filtration with both strong biological capacity and effective mechanical polishing.

A large canister filter is ideal for most keepers, offering high turnover, good particulate removal, and the ability to customise media. In larger systems, a sump is an excellent upgrade, providing even greater media volume, excellent gas exchange, and the option to hide heaters or other equipment out of sight. Additional circulation from guarded powerheads or return outlets can be used to mimic the lively water movement of the Lower Congo, but care must be taken to provide resting zones where the puffer can wallow undisturbed.

No filter, however, can replace good husbandry.

Clean, stable water is non-negotiable:

Keep nitrates below 15 ppm, ideally as close to zero as possible.
Change at least half the water weekly. Many keepers prefer larger or more frequent changes to maintain pristine conditions.
In sandy tanks, waste can accumulate beneath the surface. Gently siphon or stir sections of the substrate during maintenance to prevent compaction and the development of anaerobic pockets. In heavily structured scapes with rocks, wood, or roots, take care to prevent detritus from collecting in crevices where it may degrade water quality.

For a species adapted to one of the most oxygen-rich freshwater environments on earth, consistently high water quality and excellent oxygenation are the foundation of health.

A well-maintained system not only supports longevity but also allows T. miurus to display its full range of natural behaviours.

Why Keep Nitrates Low?

Like all puffers, Tetraodon miurus is highly intolerant of long-term deterioration in water quality. Studies on freshwater fishes show that chronic nitrate exposure can lead to:

Suppressed immune function, increasing vulnerability to parasites and bacterial infections
Reduced growth and feed efficiency, limiting condition and vitality
Shortened lifespan and long-term health decline

For the Congo Puffer, water quality is not just about survival. This is a species adapted to the pristine, oxygen-rich waters of the Lower Congo, and it thrives only when those conditions are reflected in captivity. When kept in clean, low-nitrate water, miurus displays its most vivid colours, strikes boldly from concealment, and settles into the confident, interactive behaviour that makes it such a remarkable fish to keep.

Inflation

The Congo Puffer’s most famous defence is its ability to inflate.

When threatened, Tetraodon miurus rapidly gulps water and expands into a rigid ball with spines raised in every direction. In the fast, predator-rich waters of the Lower Congo, this sudden transformation makes it far more difficult to be swallowed.

In captivity, this behaviour should remain rare. It is important never to provoke inflation deliberately, as the process is exhausting and can be dangerous to the fish if repeated unnecessarily.

Some keepers report occasional “casual” puffs in relaxed individuals. These brief, unexplained inflations are thought to help exercise the muscles used in defence and are not a cause for concern.

Prolonged inflation, however, is always a warning sign. It suggests that the fish feels unsafe or is experiencing environmental stress. Checking water quality, reviewing recent changes, and removing possible disturbances are the first steps in allowing the fish to calm and return to normal.

Inflation is one of the most striking spectacles of the pufferfish family, but for T. miurus in the aquarium, it should be seen rarely and only under natural circumstances.

Toxicity and Toxin Origin

Scientific evidence from African freshwater puffers indicates that Tetraodon miurus is capable of carrying tetrodotoxin (TTX), a potent neurotoxin best known from marine species such as the Japanese fugu.

Direct studies on miurus are limited, but closely related species have been shown to contain TTX in the skin, gonads, and liver, with muscle tissue usually much less affected. As with other freshwater puffers, toxicity is not fixed.

Levels vary with diet, habitat, and season, reflecting the role of toxin-producing bacteria and microorganisms that enter the food chain through prey items.

Puffers raised on TTX-free diets are known to lose toxicity, which confirms that the toxin is accumulated rather than produced internally. Compared to highly toxic marine puffers, African freshwater species such as miurus appear to carry lower and more variable concentrations. There is no evidence that this species reaches the lethal levels found in its marine relatives, although its tissues should still be regarded as potentially toxic.

Implications for Aquarists

For aquarium keepers, this is almost entirely a matter of scientific interest. Tetrodotoxin is a poison, not a contact venom, so there is no risk from normal aquarium care, maintenance, or handling.

The only real danger is through consumption, and since the toxin is heat-stable, cooking does not remove it. In practical terms, Tetraodon miurus should be appreciated for its remarkable biology, but its potential toxin profile has no bearing on day-to-day care in captivity.

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.