In Search of the Peaceful Puffer

Author: Neale Monks

The puppy-dog looks and playful demeanors of the pufferfishes belie a notorious reputation for nipping, territoriality, and aggression—are any of them peaceful enough for a community tank?

Intriguing Oddballs

Pufferfish are among the most popular oddball fishes for freshwater and brackish-water aquaria. They are very entertaining fish, full of life and constantly on the move. Most also seem to be quite intelligent, quickly learning to recognize their owners and often becoming tame enough to be hand fed. While puffers can be fussy about water chemistry and filtration, they are otherwise very adaptable and present the aquarist with few serious problems. In fact, the most widely traded species can be considered hardy and easy to keep. The icing on the cake is that pufferfish are very effective snail destroyers, and a tank with a pufferfish in it is a tank without snails.

In short, puffers are cute, hardy, and useful fish for the home aquarium. So why doesn’t every aquarist keep them? The main problem with puffers is their behavior; they may look sweet, but many are surprisingly temperamental, while others like to bite chunks out of the fins of slow-moving tankmates. Some species are very tolerant and accommodating while young, but become much more solitary and aggressive as they mature. Complicating matters further is that their social behavior can be unpredictable, even within species, and many aquarists have watched a seemingly well-behaved pufferfish turn into a psychotic killer overnight.

Is My Puffer Aggressive or Hungry?

Not all species of pufferfish have the same reasons for biting their tankmates. Some take nips out of all sorts of things because they’re hungry. In the wild, puffers scour plants and rocky areas looking for their preferred prey, and in the process they take experimental bites out of anything that looks edible. Anyone who has kept pufferfish will recall their intensely curious behavior, swimming up and down plants and into caves as they examine every inch of the aquarium for food. While this is a useful behavior in their natural habitat, in captivity it can lead to bad habits like taking chunks out of plastic tubing, destruction of plants, and yes, fin-nipping.

However, other puffers, particularly the small freshwater species of the genus Carinotetraodon, fiercely defend their territories. They will attack tankmates not out of hunger, but out of anger. Superficially, this would appear easy enough to work around: simply give the fish enough space that it doesn’t feel that its territory is threatened. In practice though, these small pufferfish are rarely kept in large enough aquaria for this to be a viable solution. After all, who’s going to set aside 40 gallons for a fish little bigger than a neon tetra?


A few puffers appear to be dedicated fin-nippers, viewing the bodies of larger or slow-moving fish as nothing more than “sushi on the go.” These fish are very difficult to keep in community tanks. Chelonodon patoca is one such puffer, and while otherwise non-aggressive and easy to keep, mixing it with other fish can be a bit of a gamble. Auriglobus species, on the other hand, are not just fin-nippers but actively hostile, territorial fish with a reputation for being among the meanest pufferfish out there.

For this article, I’ve narrowed the list of potential species for the community tank down to five species, all of which are widely traded and easy to obtain. Two are brackish-water species, Tetraodon biocellatus and Tetraodon fluviatilis, commonly known as the figure-eight puffer and the spotted puffer, respectively. Since these fish need brackish water, they’re obviously not candidates for freshwater community tanks, but are often proposed as tankmates for fish like monos, scats, and archers. The remaining three species are all strictly freshwater species: one from South America, Colomesus asellus, and two from Southeast Asia, Carinotetraodon lorteti and Carinotetraodon travancoricus.

Brackish-Water Puffers

Tetraodon biocellatus

Common Name: Figure-eight puffer

Size: 6 cm (2½ inches)

Origin: Southeast Asia

Water Chemistry: Slightly brackish; specific gravity 1.005 ideal

Social Behavior: Juveniles are peaceful, adults can be aggressive, territorial fin-nippers

Community Tank: Not advised, but possible

Tetraodon biocellatus is certainly an attractive fish. It is greenish-brown with a cream-colored belly, and the upper half of the body is covered in yellow squiggles and spots. There are usually two large yellow circles on the top, and it is from these that the fish gets its common name, the figure-eight puffer. As the fish matures, the markings become more complex, with additional spots and squiggles appearing until the fish looks almost leopard-like in the complexity of its coloration.

Figure-eight puffers are somewhat intolerant of their own kind, and while they don’t fight to the death, they certainly will nip one another with annoying regularity. Some, perhaps the females, will actually coexist more or less amicably provided they are not overcrowded, but others, presumably territory-holding males, are very intolerant and feisty.

As with intraspecific aggression, there is considerable variation with regard to how figure-eight puffers view other species of fish kept with them. Generally, small gobies tend to be ignored by most specimens, and so keeping fish like bumblebee gobies is a relatively safe bet. On the other hand, midwater fish like mollies, glassfish, and orange chromides, which thrive in the same slightly brackish conditions as the figure-eight puffer, tend to be more of a gamble.

Problems can range from occasional fin-nipping to all-out persecution of tankmates. Presumably, territoriality has something to do with this, and it is probably wise to consider figure-eight puffers as being similar to territorial dwarf cichlids, except with a bit more firepower, thanks to that razor-sharp beak of theirs! In a large, under-stocked tank, it may be worth experimenting with tankmates, but you do need to be prepared to move either the puffer or its tankmates at the first sign of trouble.

Tetraodon fluviatilis

Common Name: Spotted puffer

Size: 15 cm (6 inches)

Origin: India and Southeast Asia

Water Chemistry: Brackish, at least specific gravity 1.010

Social Behavior: Peaceful when young, but almost always becomes territorial and aggressive

Community Tank: No, except perhaps in a large tank with hardy, fast-moving tankmates

The spotted puffer Tetraodon fluviatilis—as well as its close relative, Tetraodon nigroviridis—is much more difficult to keep in a community tank than the figure-eight puffer. As well as being territorial, these fish are large and predatory. Potentially reaching as much as 20 cm (8 inches) in length, even the more typical 12- to 15-cm (4½- to 6-inch) specimens seen in aquaria are perfectly capable of taking big chunks of flesh out of fast-moving species like scats and monos.

Broadly speaking, juveniles can be considered relatively harmless fish that work well in communities of hardy, sturdy species, and it is only as they mature that they become both more intolerant of one another and aggressive toward their tankmates. Usually, mature spotted puffers end up being kept on their own.

Freshwater Puffers

The two puffers I’ve chosen in the genus Carinotetraodon are truly freshwater puffers, which on paper at least should make them easier to house and slot into a community tank.

Carinotetraodon travancoricus

Common Name: Dwarf puffer

Size: 2½ cm (1 inch)

Origin: Southeast Asia

Water Chemistry: Neutral freshwater

Social Behavior: Surprisingly aggressive for its size

Community Tank: Sometimes compatible with catfish, but otherwise not recommended for community tanks

At barely 2½ cm (1 inch) when fully grown, the dwarf puffer Carinotetraodon travancoricus is so small that it is hard for many people to imagine them posing much of a threat to any fish kept with them. Nonetheless, they are fin-nippers and will attack any small fish in the tank kept with them. On the other hand, larger fish may simply view these tiny pufferfish as food. Small suckermouth catfish, such as Ancistrus and Otocinclus spp., usually work out well. Small, heavily armored thorny catfish, for instance Amblydoras hancockii, might also be an option, but bear in mind these catfish need to be kept in groups and are also nocturnal, so you won’t see them much.

Dwarf puffers are best kept with their own kind. Juveniles form loose groups, while adults are territorial, so it is necessary to budget around 8 gallons per fish if you don’t want them to fight.

Carinotetraodon lorteti

Common Name: Red-eyed puffer

Size: 5 cm (2 inches)

Origin: Southeast Asia

Water Chemistry: Freshwater, ideally soft and slightly acidic

Social Behavior: Surprisingly aggressive for its size

Community Tank: Not recommended

The red-eye puffer Carinotetraodon lorteti is larger and more overtly aggressive than the dwarf puffer. While dwarf puffers tend to ignore one another provided they are not overcrowded, red-eye puffers are very intolerant of their own kind. Although attractive and comical fish, they are very difficult, probably impossible, to house in community tanks.

Colomesus asellus

Common Name: South American puffer

Size: Rarely more than 8 to 10 cm (3 to 4 inches)

Origin: Brazil

Water Chemistry: Freshwater, ideally soft and slightly acidic

Social Behavior: Nervous, rarely aggressive, but can be a fin-nipper

Community Tank: Possible, but not a reliable community tank resident

Probably the most widely traded freshwater pufferfish is the South American puffer, Colomesus asellus. Given around 18 to 25 gallons each, multiple South American puffers can be maintained together without problems, and in the wild, they are known to form large schools. They are equally tolerant of other aquarium fish, and are in fact rather nervous and easily frightened.

So far so good, but there is a catch—these fish can be fin-nippers. Over the last 12 months my own specimen has exhibited this tendency, but in a remarkably inconsistent way. A few species in the tank were routinely nipped and eventually removed to other quarters. These included platies, mollies, and various small gobies.

On the other hand, glassfish, halfbeaks, hatchetfish, and cardinal tetras have shown little or no evidence of being harassed. Broadly speaking, South American puffers can work well with active, fast-moving fish but shouldn’t be trusted with long-finned, passive, or slow-moving species. They’re not perfect, but maybe these puffers do come reasonably close to being community-safe puffers.

The Bottom Line

None of the commonly traded pufferfish can be considered reliable, completely trustworthy community fish. Many aquarists are used to predatory and territorial fish, of course, and very often such fish can work well in communities of larger species. Climbing perch, big cichlids, predatory catfish, bichirs, and stingrays are all examples of fish that aren’t technically community fish but usually turn out to be well-behaved and peaceful when placed with the right tankmates.

Puffers are different. The small species are often too aggressive or nippy to be mixed with fish of similar size, but are themselves likely to be threatened by substantially larger tankmates. The bigger puffers are usually predatory as well, and they make risky additions to community tanks. Even the mild-mannered South American puffer doesn’t play nicely often enough to be recommended as a community fish. From its size and demeanor it should get along well with mid-sized fish like Corydoras, angels, and gouramis, but all of these fish are likely to get nipped sooner or later.

For any aquarist wanting to keep pufferfish, a single-species (and often single-specimen) aquarium usually ends up as the best way to go. Some experienced pufferfish keepers don’t consider this a bad thing. Pufferfish are notoriously intolerant of high nitrate levels and low oxygen concentrations, so keeping them in their own tank makes life much easier on both these counts. Large water changes are thought to be helpful, with as much as 50 percent needing to be changed on a weekly basis. No matter how cute pufferfish seem, they aren’t the easiest fish to look after, and any aquarist tempted to keep them needs to think carefully about their maintenance beforehand.

Recommended Reading

There are two good pufferfish books available to aquarists interested in these entertaining yet difficult fish. Pufferfish (Ringpress Books, 2002), written by Chris Ralph, covers all the basics. Klaus Ebert’s The Puffers of Fresh and Brackish Waters (Hollywood Import & Export, 2001) will appeal to the more dedicated pufferfish enthusiasts, and it includes numerous photographs on just about every fresh- and brackish-water pufferfish traded.

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