Eyespot pufferfish (Tetraodon biocellatus)

Recognise the freshwater eyespot puffer

The Eyespot pufferfish (Tetraodon biocellatus) is a freshwater member of the puffer family Tetraodontidae from Indochina, Malaysia and Indonesia. It reaches 8 cm and suits a keeper prepared to manage shell-on feeding, water quality and compatibility deliberately. Keeping one fish is the lower-risk social plan, while any community needs careful screening and observation. FishBase now lists it as Dichotomyctere ocellatus, treating Tetraodon biocellatus as a synonym.

FishBase records a maximum length of 8 cm total length for male or unsexed fish. Plan around that maximum rather than the smaller dispatch measurement. This is an active, substantial fish despite its modest length, and its aquarium must provide both open swimming room and enough structure to provide cover.

Understand its natural feeding behaviour

In nature it feeds on snails and other organisms living on or near the bottom. Its beak-like mouthparts crush shelled prey, and its teeth continue to grow. Aquarium feeding therefore has two connected jobs: provide suitable nutrition and give the fish regular work against shells. Soft frozen food can add variety, but it cannot replace snails and unshelled shellfish as the central teeth-management foods.

FishBase identifies the species as freshwater and explicitly distinguishes it from brackish-water puffers. Build its aquarium as a freshwater system rather than adding marine salt by habit. Its recorded distribution covers Indochina, Malaysia and Indonesia.

Decide whether the husbandry suits you

Puffers may inflate in response to a threat. Do not provoke this behaviour or lift the fish into air to see it happen. Arrange routine work calmly and keep the fish submerged during any necessary transfer.

Choose the dispatch size with the adult plan in mind

One purchase supplies one animal of the option selected. The live size selector may show the dispatch labels 2–3 cm, 3–4 cm, 5 cm and 7–9 cm; use that selector for the choice presented when you order. The size you select is the size supplied, not the adult size. Every option therefore needs the same adult aquarium plan rather than a smaller permanent home for a smaller dispatch grade.

Sex is guaranteed only when the selected option explicitly states male or female. This Eyespot pufferfish listing has no sex-guaranteed option.

The gallery images are representative, based on reference photographs of this species, so colours can look slightly different from the live animal.

Start with the decisive space and water figures

Seriously Fish recommends an aquarium base of at least 75 × 30 cm, equivalent to about 68 litres in the cited 75 × 30 × 30 cm example, for a fish planned around 8 cm standard length. Base dimensions matter because they determine the usable swimming area and the room available for roots, branches, plants and separate routes around the aquarium.

These figures form a starting point for one fish. Extra companions increase the need for usable floor area, cover and filtration capacity; litres alone do not show whether the layout can separate animals or let a pursued fish retreat.

This puffer suits an established freshwater aquarium built around its needs, not an impulse addition to a mixed tank. Keep the biological demands, shell-on diet and compatibility screen together when comparing it with fish in the loaches and oddballs collection.

Build cover with open swimming routes

Use a freshwater aquarium with a base of at least 75 × 30 cm and an example volume of about 68 litres for one. Do not judge suitability by volume alone: a tall, narrow aquarium can hold the same litres while offering less horizontal room than the recommended footprint. Measure the internal base and account for large décor that removes usable space.

Divide the footprint into three functions

A heavily planted arrangement with roots and branches provides cover, while open gaps prevent the aquarium becoming a maze with no sustained swimming route. Look through the aquarium from each end. If décor blocks every route, remove or reposition a piece.

Choose a sandy substrate for the recommended layout. Floating plants can diffuse the light, while rooted and attached plants give the fish cover at different heights. Soft-leaved plants may be chewed, so check their condition during routine observation and remove loose pieces before they collect around the filter intake.

Check the layout before introducing the fish

1. Confirm that the filter intake and outlet remain clear after planting.
2. Leave enough room to siphon food remains without dismantling the aquarium.
3. Make sure roots and branches are stable and cannot shift during maintenance.
4. View the tank from the front and both ends to confirm that several covered areas are present.
5. Keep at least one uninterrupted swimming route through the open area.

For more than one puffer, the same décor must create genuinely separate routes rather than one central cave that every fish must contest. A larger aquarium is essential, but more litres only help when the layout also reduces repeated face-to-face encounters. Complete the hardscape before arrival so the fish enters a settled environment rather than one undergoing repeated redesign.

Mature the filter before the fish arrives

A working biological filter is essential. The RSPCA explains that fish release toxic ammonia; beneficial bacteria in a mature filter convert it first to nitrite, which is also toxic, and then to the safer nitrate. This puffer is particularly sensitive to deteriorating water conditions, so the aquarium must be mature and stable before the fish is introduced.

If this is a new aquarium, follow the steps in our first tropical tank guide before choosing an arrival date. Running a filter for a short time is not the same as establishing the bacterial population needed to process animal waste. Test during maturation and only introduce livestock when the filter is demonstrably handling the waste load.

Match flow to the aquarium

For the cited aquarium of about 68 litres, Seriously Fish uses a turnover of four to five times the aquarium volume per hour and gives a filter rating of roughly 270–340 litres per hour. Treat the manufacturer’s rating as a selection guide: filter media, pipework, debris and head height can reduce actual flow.

Choose filtration for biological capacity as well as headline flow. Shellfish feeding can leave fragments that need manual removal; the filter should not be expected to hide poor feeding hygiene. Observe where debris settles during the first few feeds and make that area part of the siphoning route.

Add livestock gradually whenever the aquarium population changes. A mature filter supports a known waste load, and a sudden rise in feeding can outpace its bacterial population. Test after any significant stocking or feeding change rather than assuming yesterday’s stable result still applies.

Hold freshwater values inside the species range

Maintain this puffer at 22–26°C, pH 6.5–7.5 and 5–12 dGH. FishBase’s recorded freshwater environment and the Seriously Fish aquarium range agree on these values. Stability within the range is more useful than repeatedly adjusting water towards a single point.

Begin with measured tap and aquarium water rather than choosing products first. Our water chemistry guide explains what the main values mean, and the water matcher can compare your measured results with this range. Check temperature with a separate aquarium thermometer as well as the heater setting.

Use consistency as the decision rule

• If the aquarium stays inside the range, keep the routine consistent rather than chasing an exact midpoint.
• If a water change causes a marked shift, compare the replacement water with the aquarium before the next change.
• If temperature varies through the day, inspect heater operation, room conditions and water circulation.
• If pH or hardness sits outside the range, plan any correction gradually and measure each stage.

Set the aquarium up as freshwater. Do not add marine salt merely because some puffers are brackish-water fish. Salinity changes affect plants, biological filtration and every intended companion, and FishBase identifies this animal as a freshwater species rather than a brackish one.

For the approximately 68-litre example, Seriously Fish suggests roughly 50–75 W of heating when the room is around 20°C. Heater power depends on aquarium volume and room temperature, so use that figure as a worked example rather than a universal wattage. Position the heater where circulation distributes warmth and verify the result at the opposite end of the aquarium.

Use shell-on foods to manage the teeth

Build the diet around snails and unshelled shellfish, with worms and other live or frozen foods for variety. Seriously Fish specifically names snails, crab legs and prawns among appropriate foods. The shell is functional as well as edible because the puffer’s teeth grow continuously and need regular wear.

Give each food a clear role

Offer a portion the fish can work through while you observe it, then remove uneaten flesh and shell fragments before they decay. Adjust the next portion according to what was actually eaten rather than adding more because the fish remains attentive at the glass. Shellfish remains can quickly become a water-quality problem in a warm aquarium.

Present foods in the accessible feeding area planned during aquascaping. This lets you confirm that the fish has found the meal and makes later siphoning practical. Rotate suitable foods, but keep shell-on prey regular; a sequence of soft foods may provide calories without doing the mechanical work needed by the teeth.

Watch how the mouth is used

• Normal feeding decision: continue the established variety when the fish approaches, grips and crushes appropriate food effectively.
• Food remains untouched: remove it, test the water and compare the fish’s breathing, swimming and appearance with its usual condition.
• Repeated difficulty gripping food: stop relying on soft substitutes and seek prompt health guidance before body condition falls.
• Excess fragments after every meal: reduce the portion and improve access for siphoning rather than increasing filtration flow alone.

Do not treat snails or other shelled invertebrates as ornamental companions in the same aquarium. FishBase records snails and other bottom-living organisms as natural prey, so their presence may trigger feeding rather than peaceful coexistence.

Use testing to set the maintenance rhythm

Regular partial water changes are essential because this puffer is sensitive to deteriorating conditions. For the general weekly routine, OATA’s freshwater guidance for tetras and pencilfish is broad rather than puffer-specific: it recommends changing 25% at least once a week, testing at least once a week, keeping ammonia and nitrite at zero, and preventing nitrate from rising more than 20 mg/l above the normal tap-water level. Use that as a baseline and increase attention when feeding, stocking or test results demand it.

Complete the weekly sequence in one order

1. Observe the fish before disturbing the aquarium.
2. Test the water and write down the results.
3. Siphon shell fragments, uneaten food and other settled waste.
4. Replace about 25% with conditioned water matched as closely as practical for temperature.
5. Check the filter intake, outlet and heater after refilling.
6. Observe swimming and breathing once the aquarium has settled.

Treat replacement tap water with a conditioner that addresses chlorine or chloramine before it enters the aquarium. Sudden changes in temperature or chemistry undermine the stability that the maintenance routine is meant to protect.

If filter media needs cleaning, do not run it under the tap. Rinse it lightly in the aquarium water removed during a partial water change. Do not replace every mature medium at the same time. The beneficial bacterial population is part of the aquarium’s waste-processing system, not dirt to be sterilised away.

Respond to the result, not the calendar alone

If ammonia or nitrite appears, reduce the immediate pollution source, remove food remains, make an appropriate partial water change and inspect the filter. Follow with further tests until the result returns to zero. If nitrate rises faster than usual, review portion size, waste removal and total animal load before simply making each water change larger.

Record results in the same units each week. A short sequence of readings reveals gradual change more clearly than memory and helps connect a shift with a blocked filter, heavier feeding or an alteration to the aquarium population.

Acclimatise with a prepared freshwater aquarium

Prepare the aquarium and testing equipment before delivery. Someone must be present to receive the live fish, and the aquarium should already be heated, filtered and within 22–26°C, pH 6.5–7.5 and 5–12 dGH.

Follow the current delivery and Live Arrival Guarantee policy for every arrival.

Work through arrival in the required sequence

1. Receive the parcel in person so the live fish is not left unattended.
2. Start filming while the parcel is still sealed, with the outer box visible.
3. Open the parcel in one continuous take and show the fish while it remains inside the sealed bag.
4. Float the bag for 20–30 minutes before releasing the fish.
5. Transfer the fish without pouring the bag water into the aquarium.

Keep the aquarium layout unchanged while the fish settles. Seriously Fish recommends planted cover, roots or branches and open swimming space, so the prepared aquarium should already provide shelter and a clear route through the layout.

Use the first week to establish a baseline

A newly introduced fish may use cover while it adjusts. Judge change by the combination of behaviour, breathing, feeding and water results rather than one brief moment. Avoid adding further livestock during this observation period because each addition changes both social pressure and filter demand.

Act on changes before condition declines

Learn the fish’s normal swimming, breathing, feeding response, colour and preferred resting places. A daily comparison is more useful than expecting every healthy puffer to behave identically. Observe before feeding as well as during the meal, because food anticipation can temporarily change activity.

Pair each warning sign with an action

When a change appears, start with measured water results because ammonia, nitrite, temperature and rapid chemistry shifts can produce urgent problems. Confirm that the filter is running, the intake is clear and no shellfish remains are decaying behind décor. Do not add food to test appetite repeatedly when water quality may already be deteriorating.

Contact us promptly if the change persists or the fish shows altered breathing, balance, feeding or body condition. Share the aquarium volume and base dimensions, temperature, pH, hardness, recent ammonia and nitrite results, maintenance history, foods offered and the timing of the change. Those details make the next decision more precise.

Review the first month

• Confirm that shell-on foods are being accepted and crushed effectively.
• Check whether debris consistently collects in an inaccessible area and adjust one item of décor if needed.
• Compare weekly water results for a rising trend rather than considering each test alone.
• Assess whether the fish has secure cover and an uninterrupted swimming route.
• Keep the population stable while feeding, filtration and behaviour settle into a repeatable routine.

Choose one fish or plan a deliberate group

Keeping one Eyespot pufferfish is the lower-risk social plan. FishBase records aggression towards its own species, while Seriously Fish reports that individuals kept alone usually live longer in captivity. A single fish also makes it easier to monitor food intake, mouth function and waste from shell-on meals.

Do not buy a casual pair or trio as a compromise. If you decide to keep more than one, Seriously Fish advises trying at least four so aggression is distributed through the group, and only in a suitably large aquarium. This is not a claim that four will always coexist: personalities and pressure within the group still require close observation.

Test the group plan before choosing fish

Watch for repeated chasing, one animal controlling the feeding area, persistent hiding, fin damage, colour change or declining condition. A brief pause behind cover is different from being prevented from swimming and feeding normally. Intervene according to the repeated pattern rather than waiting for visible injury.

The 75 × 30 cm footprint and approximately 68-litre example are the planning minimum for one fish, not a formula for four. Group planning requires more space, more cover, additional feeding positions and filtration that can handle the increased waste. Do not multiply 68 litres mechanically and assume the result guarantees compatible territories; the shape and arrangement of the aquarium remain decisive.

Screen every community companion

A community aquarium is possible only with careful selection and observation. Seriously Fish warns that this puffer tends to nip slow-moving or long-finned fish, so avoid those body and fin types. In freshwater it has been kept with fast-moving characins, rasboras and barbs, but those examples are a screening direction rather than universal tank-mate approval.

Apply five checks to every proposed companion

1. Swimming speed: choose fish able to move away rather than hover within easy nipping range.
2. Fin shape: avoid long, trailing fins that invite repeated attention.
3. Freshwater requirements: confirm that the companion fits 22–26°C, pH 6.5–7.5 and 5–12 dGH.
4. Adult size and space: assess the mature animal and the aquarium footprint, not the dispatch size.
5. Feeding behaviour: make sure each animal can eat its intended food without being displaced.

Snails and shelled invertebrates belong in the prey assessment, not on a peaceful companion list. FishBase records snails and other bottom-living organisms in the natural diet, and the aquarium diet deliberately uses shelled prey. Avoid adding ornamental snails or similar invertebrates that you intend to keep as display animals.

Other Eyespot puffers require the separate group plan rather than the ordinary community screen. Aggression towards its own species makes a pair especially poor as an automatic choice. If several are attempted, start with at least four in a substantially larger, structured aquarium and keep a mature separation option ready.

Observe the relationship after introduction

Check who controls the open route, feeding area and cover. Repeated pursuit, nipping, exclusion from food or persistent hiding means the combination is failing even if the fish share water values. Separate animals before declining body condition or extensive fin damage develops.

For a stocking and compatibility assessment, contact us with the aquarium’s base dimensions and volume, current inhabitants with adult sizes, measured water values and the proposed number of puffers. The honest uncertainty is individual behaviour: a species that passes the initial screen still needs observation after introduction.

Answer the key buying questions

How big does the Eyespot pufferfish get?

It reaches 8 cm. Plan the aquarium around that adult maximum rather than its dispatch size.

What size aquarium does an Eyespot pufferfish need?

Plan at least a 75 × 30 cm aquarium base, about 68 litres in the cited 75 × 30 × 30 cm example, with mature filtration, sand, planted cover, roots or branches and open swimming space.

How many Eyespot pufferfish should I keep together?

Keeping one alone is the lower-risk plan. If several are attempted, Seriously Fish advises at least four in a suitably larger aquarium, with several covered routes and a mature separation aquarium ready if aggression persists.

Is an Eyespot pufferfish suitable for a beginner?

Choose it only if you can provide regular shell-on foods, maintain a mature freshwater aquarium, test the water and assess compatibility carefully. Its teeth, sensitivity to deteriorating water and potential fin nipping require deliberate daily observation.

What does an Eyespot pufferfish eat?

Feed snails and unshelled shellfish such as prawns or crab legs regularly, with worms and other live or frozen foods for variety. The shell helps wear its continuously growing teeth, and uneaten remains should be removed promptly.

What temperature and pH does this fish need?

Maintain freshwater at 22–26°C, pH 6.5–7.5 and 5–12 dGH. FishBase’s recorded environment and the Seriously Fish aquarium range agree on these values.

Is it aggressive or likely to nip fins?

FishBase records aggression towards its own species, and Seriously Fish warns that it tends to nip slow-moving or long-finned fish. Keeping one puffer is the lower-risk plan, and those companion types should be avoided.

Which kinds of animals can live with it?

Fast-moving characins, rasboras and barbs are the freshwater examples named by Seriously Fish, but every candidate needs screening for shared water needs, swimming speed, adult size and feeding access. Avoid slow-moving or long-finned fish, ornamental snails and similar shelled invertebrates intended as companions.

How does this fish arrive alive in the UK?

Start filming every delivery continuously while the parcel is still sealed, then show it being opened and the animal still inside the sealed bag. Someone must be present to receive it; float the bag for 20–30 minutes before releasing the fish, and never pour the bag water into the aquarium.

Check the care references

• FishBase species summary — accepted identity, family, freshwater environment, distribution, natural diet, conspecific aggression and maximum recorded length.
• Seriously Fish species profile — aquarium footprint, water range, layout, filtration, diet and compatibility.
• OATA freshwater guidance — broad testing and maintenance baseline for tetras and pencilfish.
• RSPCA aquarium environment guidance — biological filtration and aquarium waste processing.