The figure 8 puffer (Dichotomyctere ocellatus, formerly Tetraodon biocellatus) is the best-behaved of the medium puffers and the one most often sold under a false description. It comes from the estuaries and lower river reaches of Malaysia, Borneo, Sumatra and Thailand, and it needs low brackish water for its whole life — not the freshwater tank it is usually displayed in.
Figure 8 Puffer Care at a Glance
| Parameter | Value |
|---|---|
| Scientific name | Dichotomyctere ocellatus |
| Adult size | 3 in (8 cm) |
| Lifespan | 10–15 years |
| Minimum tank | 15 gal single; 20–29 gal preferred |
| Water type | Low brackish, SG 1.005–1.008 |
| Temperature | 75–82°F (24–28°C) |
| pH | 7.5–8.2 |
| Hardness | 10–20 dGH |
| Diet | Snails, clams, bloodworms, mysis |
| Temperament | Curious, semi-aggressive, fin-nipper |
Figure 8 Puffer Tank Size
Fifteen gallons is the minimum for one figure 8 puffer, with 20 to 29 gallons much better. A 24-inch footprint is the practical floor. For a second fish, add at least 10 gallons and enough hardscape to give each one its own end of the tank — and be ready to separate them if the chasing does not settle within a fortnight.
- Sand substrate, driftwood, smooth rock and caves.
- Brackish-tolerant plants only at this salinity: java fern, anubias, crypts and marimo will hold at SG 1.005; most stem plants will not.
- Moderate flow with an oversized filter — a shellfish diet is messy.
- Lid. They are strong swimmers and follow food upward.
Salinity: Why Freshwater Is Not Enough
A figure 8 puffer will live in freshwater for a year or two, which is exactly why the myth persists. Long term it develops poor colour, reduced appetite, susceptibility to fungal and bacterial infections, and a lifespan cut roughly in half.
- Use marine salt mix, never aquarium tonic salt or table salt.
- Target specific gravity 1.005–1.008, roughly 2.5–4 oz of salt per 10 gallons. Measure with a refractometer.
- Dissolve the salt fully in the change water at matched temperature, then add.
- If converting an existing freshwater tank, raise salinity by no more than 0.002 SG per week so the biofilter can adapt.
Full salinity tables are on the water parameters page.
Figure 8 Puffer Food
Snails are the staple — ramshorn, bladder and small nerites — supported by small clams and cockles in shell, frozen bloodworms, mysis and chopped krill. Feed daily as a juvenile, every other day as an adult, and always include something with a shell so the beak stays worn. See the feeding guide.
Figure 8 Puffer Tank Mates
The best figure 8 tank is a species tank. Where company is attempted it has to be brackish-tolerant, fast and short-finned:
- Sometimes work: bumblebee gobies, knight gobies, orange chromides, mollies acclimated to brackish water — in 29 gallons or more.
- Do not work: anything long-finned, anything slow, all shrimp, all ornamental snails, and every freshwater community fish that cannot handle salt.
- Other puffers: a second figure 8 is possible in a large, well-broken-up tank; green spotted puffers are too aggressive to pair with them long term.
General rules on the tank mates page.
Behaviour and Health
Figure 8 puffers are alert, food-motivated and quick to recognise their keeper. They rest on the substrate and on leaves — this is normal, not illness. Watch for the specific problems this species runs into:
- Ich after a temperature drop. Treat at half dose; puffers are scaleless. Raising salinity toward 1.010 also helps.
- Internal worms in wild-caught fish. Nearly all figure 8s are wild-caught. Quarantine and deworm on arrival.
- Overgrown teeth if the diet drifts to bloodworms alone — see the teeth page.
- Bloating after a large meal is normal and passes; persistent swelling is not — see puffing up and bloating.
Symptom-by-symptom guides are indexed at figure eight puffer diseases.
Frequently Asked Questions
What size tank does a figure 8 puffer need?
Fifteen gallons is the minimum for one adult, with 20 to 29 gallons preferred and a 24 inch footprint as the practical floor. Add at least 10 gallons and plenty of hardscape for a second fish.
Do figure 8 puffers need brackish water?
Yes, for their whole lives. Target specific gravity 1.005 to 1.008 using marine salt mix, which is roughly 2.5 to 4 ounces per 10 gallons. They survive freshwater for a year or two, then decline in colour, appetite and lifespan.
What do figure 8 puffers eat?
Snails as the staple, plus small clams and cockles in shell, frozen bloodworms, mysis and chopped krill. Feed daily as a juvenile and every other day as an adult, always including a shelled item to wear the beak down.
What are good figure 8 puffer tank mates?
A species-only tank is safest. In 29 gallons or more, bumblebee gobies, knight gobies, orange chromides and brackish-acclimated mollies sometimes work. Long-finned fish, slow fish, shrimp and ornamental snails never do.
How long do figure 8 puffers live?
Ten to fifteen years in correct low brackish water. Kept permanently in freshwater the same fish typically manages five to seven years, which is where the reputation for a short lifespan comes from.
Can figure 8 puffers live with green spotted puffers?
Not long term. Green spotted puffers become considerably more aggressive as they mature and need much higher salinity as adults, so the two species end up incompatible on both temperament and water chemistry.