Tetraodon biocellatus, the Figure-8 Puffer, is a small brackish water puffer from Southeast Asia, which will remains at or just above 3 inches (8cm) total length in captivity. It is one of the most attractive if not the most attractive of the common (in stores) puffers, and it will not lose its looks with age. It is highly adaptable to water conditions, surviving even in fresh water (FW) for extended periods, but will be weaker, stunted, and more subject to disease or infection there. It is best in brackish water (BW) in my experience but is not at all demanding as to the exact specific gravity.

It will frequently tolerate conspecifics (other fish of the same species) as tank mates in sufficiently large and visually complex tanks, as it is one of the least aggressive of the hunter/predator puffers. However, as pointed out in earlier articles (1,2,3 ) it is impossible to predict the behavior of any particular specimen. There is a wide range of “personality” within a species, just as there is between species, some individuals of even the milder (for puffers) species being incurable nippers or even killers.

Similar to its cousins, it is best in a visually and spatially complex environment, with no toxic metabolites (ammonia or nitrite) and low nitrate and generally high water quality. As these are active fish, they need room to swim (exercise) and explore, but will appreciate some refuge (cave or overhang or plant thicket) where they can “feel” secure.

Tetraodon biocellatus, the Figure-8 Puffer.
Photo credit: Steve Tapril, The Puffer forum

The Figure-8 suffers from too many names, both common names and scientific names. Currently, T. biocellatus is accepted as correct, but it has been called by several other scientific names, which actually may belong to distinct other species. In the trade the F-8 is frequently confused with the Ceylon Puffer (T. fluviatilis), which is well more than twice as long and several times the mass as an adult, and may or may not be less colorful at purchase.

The Ceylon in my experience tends to have its colors fade a bit with age, while the Figure-8 does not fade at all. To differentiate the two fish, ignore the dorsal markings that give the Figure-8 its common name, and the dorsal saddle-like markings of the Ceylon, which can also appear to form a figure-8. Their colors at maturity are quite different, but that may be hard to detect at sale size when looking at live small fish in a store especially if you have only seen poorly reproduced pictures on the web or in books and magazines.

T. biocellatus’ species name “biocellatus” means “two eyespots”, and it does have two dark spots, ringed or outlined in light yellow to greenish gold, on each side. The first of these spots (usually slightly larger than the other) appears below the dorsal fin on each side of the fish. The second of the eyespots appears on the caudal peduncle, immediately in front of the caudal (tail) fin of the fish, again on each side of the fish. These are the diagnostic markings for this fish, not the dorsal figure-8, where the dorsal patterning is almost as individual as fingerprints and frequently does not resemble an “8” at all (4). The Ceylon has no such eyespots.

The Ceylon does have a number of small dark spots scattered all along the sides of the fish below the saddle-like dorsal markings, and these do show up clearly against the lighter background color of the fish (5), but nothing like two relatively large and very clear ocelli of the Figure-8. Either species many have no, a few, or many squiggles of the lighter color along with variable numbers of un-ringed dark spots on their sides, but only the Ceylon frequently has a substantial scattering of the dark, not ringed, spots along the sides.

Fish are sometimes seen in stores where the dorsal markings do not form a Figure-8, but where the two eyespots are present. There may be few or many “squiggles” of the contrasting yellowish lines on the sides of these fish. They have been called a different species, or different color variants (perhaps geographic populations?). But if the ocelli are present, for the time being it is probably better to call them all T.biocellatus. As was mentioned at the beginning of this series of articles (1), the taxonomy of this family is not clear or clean, and the hobby nomenclature is far worse. As this fish inhabits a substantial geographic area, with possibly isolated populations, geographic races with differing marking would be no surprise.

When the fish are seen in the local store, it is common for them to be in rough condition. Nipped fins, bite marks, Ich (Ichthyophthirius or White Spot), or fungus are almost to be expected, more likely some combinations of several to all of those. The things I look at most closely are activity and color (not dark bellied, not resting on the bottom constantly) with a belly that is not concave. As was the case with the South American FW puffer discussed in another article (3), a starved and hollow-bellied fish is hard to bring back to health. Such appearance may be a sign of heavy intestinal parasite load as well. Those I leave to the store’s care. If I want the fish, a few nips and bites, even Ich, will not stop me. So long as the fish has a decent profile, showing that he/she has been eating, and so long as the fish is actively swimming around the tank, the rest is readily cleared.

None of the FW or BW members of the genus Tetraodon are sexually dimorphic. That means that you cannot distinguish males and females visually by external clues or configuration. Some few full adult, very well kept, female may show the increased girth from development of eggs in the abdomen, but even that is uncommon.

These fish need quarantine (QT) when brought home. If the local store has them in FW (common), start adjusting them to at least some salt (marine mix) immediately. The QT setup should not be too small or too barren if you are setting for a group of these fish. Even when small, they may be nippy toward their tank mates. If the local store had them in plain FW, local tap water, acclimate them first to this at your house. If the store had then in brackish, you should try to match that specific gravity at home. If they were in tap water at the store, as soon as possible afterward set a slow drip of pre-dissolved marine mix into their tank. A jar or bucket with the salt solution and a piece of airline tubing for the siphon-drip, using a knot in the airline tubing or spice in a plastic airline valve to adjust the drip rate into the tank will allow very slow addition (1-2+ hours minimum, more is better if the difference is large between the two conditions). Make sure that the tank has room for the solution you are going to add (reduce the volume in the tank before you start adding the salt solution).

Initially I don’t bring up to more than 1 teaspoon of marine mix per gallon actual volume if the fish have been in tap water. That is enough to treat any Ich present, in parallel with slow increase of the temperature to 80-85F. If the fish stay active and eat well, every 3-4 days more marine mix may be added to bring the specific gravity up to 1.002-1.005 over a couple to several partials (depending on the target density that you use) with stepwise increases each time. Remember to monitor for ammonia, nitrite, nitrate, pH/KH, and specific gravity regularly during adaptation/quarantine. The quarantine period should be for a minimum of 4 weeks after the last visible symptoms of Ich or any other conditions requiring treatment have faded away. Also note that at these low densities, the FW nitrification bacteria will continue to serve their function normally.

These particular fish I tend to keep long-term in light brackish (~1.005 specific gravity). My personal feeling is that in general BW is intermediate between FW and SW for stocking purposes. If you subscribe to the “1 inch per gallon” rule for FW (highly debatable) and “1 inch per 5 gallons” for SW (equally debatable), this would put BW at 2-3 inches per 5 gallons. I do try to very roughly follow such a guideline for some BW species, but especially as puffers are such messy feeders, and considering territoriality plus activity levels I tend to be closer to but much more generous on water than SW stocking levels for the active hunter types such as Figure 8s.

Total body mass of these chunky fish is large in relation to length, and territoriality is at or near the top of the scale. For me a single smallish immature F-8 might be kept in a ten in QT for some period, but for long-term housing, a visually complex standard 15 is far better, and a 20-long perhaps ideal for a singleton. Larger volumes make water management easier. These fish are adaptable to specific gravity variations by nature. They are not at all adaptable to reduced water quality. The same nitrification bacteria will continue to operate at these densities as well as at the lower QT densities. The bacteria needed at mid-range and high-range BW are different (those are the same as SW nitrification bacteria), but that does not apply for this fish and their optimum appears to be somewhere at or just over 1.005 specific gravity.

The fish can be adapted to your feeding during QT as well. The same foods set out before in the articles listed in the footnotes (12) should be used. If the fish are less than an inch long, daily feeding is a good idea. If more than one meal per day is required to make you comfortable (it is not for me), be sure you monitor the water conscientiously and do any water changes needed – these fish do not need additional stress during this period. If the fish are over an inch long, one good meal per two days is sufficient. After a “good” meal, the Figure-8s will show potbellies, at least a bit. They should not be fed to the point where they have difficulty swimming and look pregnant or massively beer-bellied. That is overfeeding and not good for the fish or the water. If you are not already culturing snails to feed the puffer(s), the QT period is a good time to start your culture (6). All puffers and most other adult fish in my care fast at least one day per week.

As the Figure-8 is just a bit smaller than the South American puffer discussed earlier and of similar (if slightly less rapid) activity and temperament, the same size allowances concerning tanks can apply, as can most of the comments made on tank decor in that article (3) with a few changes. The major change is that these fish are brackish water, so live plants are not an easy option and driftwood may not be as desirable either (it rots or decays much faster in BW, bad for the water quality). This means using largely rockwork or artificial plants and artificial wood to break up sight lines and create refuges (more than the number of fish, please, to allow choices). I also use aragonite substrates to assist in maintaining high pH (7.8-8.2 or higher) even when lower specific gravity is used. My subjective opinion is that high and stable KH (and the resulting high pH) is more significant to brackish puffers such as this one than is the salinity, but I have no controlled experimental data to prove that.

As was mentioned earlier in this series (2), marine mix does not dissolve immediately as would ordinary table salt. This requires an extra vessel (tank, Rubbermaid food-safe container, bucket) with a heater and a circulation pump (a sponge filtered powerhead is fine) to pre-dissolve the salt mixture used for water changes. At least 24-48 hours should be allowed for this. In practice, I keep a smaller tank with prepared water (7) always available. Many brackish water keepers make a point of varying the specific gravity of the tank periodically, as brackish fish are subject to regular tidal changes in the wild. I am not so conscientious about that as I once was. If the specific gravity varies a point up or down after a water change, I do ignore it, but I don’t intentionally vary the density anymore. Make-up water for topping up the tank due to evaporation losses is done with aged or disinfectant-neutralized tap water, not salted water, as the mineral content remains behind when the water evaporates. If you prepare RO (reverse osmosis) or RODI (reverse osmosis plus de-ionization) water for other purposes, this is a good use for such, but it is not at all essential so long as you maintain a good routine water partial schedule.

If you keep a group of these fish together and one individual becomes overly aggressive, nipping or biting the others, I know of no way to correct that. That individual must be isolated from its peers or damage or death may occur. Temporarily a tank divider (such as plastic eggcrate material) may be used and later removed for trial when you will be home for extended close observation. But the odds are the fish will have to be returned to the store (arrange this in advance – they may not want an aggressive adult puffer) or housed as a singleton in its own tank. For these fish this is not as stressful as it might sound. Their adult territoriality is the root cause of the community problem initially; keeping them as solitary specimens seems to suit them just fine. Like singleton Oscars and Goldfish, they quickly become even more “tame”, centered on their keeper as singletons. One interesting sidebar on this practice is that all of my longest-lived puffers to date have been singletons, mostly removed from groups due to aggression. I suspect that competitive stress, or rather its lack in a singleton tank, is the major factor there.

This species can live to ages comparable to the longer-lived cichlids and approaching that of Clown Loaches. My personal oldest Figure-8 died after more than 18 years in my care, and I’m sure that mark can be beaten. By 10-12 years the fish started showing some signs of age. The normally transparent pectoral fins (remember that puffers have no paired pelvic fins) became a bit translucent near the base, and over that time period the translucency slowly spread out to about half the fin area. Body colors held quite well throughout the fish’s’ life. The fish rarely would eat to the potbelly state puffer owners know so well, but maintained a slightly rounded to nearly flat belly area the rest of its life. The small group of singletons that I maintained for lifespan trial averaged a bit over15 years in my care, ranging from over 12 to over18 years in my care.

Figure-8s have been reported to be bred in captivity, but I have no details on the conditions used (see Ian West’s site referenced in footnote 8).

Few people are willing to do the “extra work” (primarily in preparation of the water for partials) and keep the “extra equipment” (marine mix, hydrometers and/or refractometers) required for brackish water fish. But if you have an interest in these fish, especially a relatively small and easy to keep fish such as the Figure-8 puffer, the extras turn out to be minimal, and the high-personality, truly pet fish will reward your efforts for many years to come.


1. AT LAST! A Book Devoted to Fresh and Brackish Water Puffers
2. Introduction to the Freshwater and Brackish Water Puffers
3. First Freshwater Puffer? Try South America
4. See the Fishbase entry for F-8s, where the dorsal markings are not an “8”, but two ocelli are quite clear:

5. See the Google image of T.fluviatilis (the Fishbase picture is poor), noting the lighter background color and absence of eyespots:

6. Breeding Snails for Food
7. My prepared water is made up as full-strength marine, and then diluted with aged and tempered tap water to the desired density for any particular tank.
8. Ian West’s site in the UK, http:/www.pufferfish.co.uk/ is not up at this editing. Nor could I retrieve it through the WEB archives. I hope this is temporary situation. There is much interesting and valuable information there.

Figure Eight Puffers – A Great Small Brackish Fish
By: Robert T. Ricketts



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