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  • Source: Copyright

    Species: Tetraodon biocellatus

  • Source: Copyright

    Species: Tetraodon biocellatus

  • Source: Copyright

    Species: Tetraodon biocellatus

  • Source: Copyright

    Species: Tetraodon biocellatus

  • Source: Copyright

    Species: Tetraodon biocellatus

  • Source: Copyright

    Species: Tetraodon fluvialitis

  • Source: Copyright

    Species: Tetraodon nigroviridis

Green, spotted pufferfish — and how to tell them apart

By Neale Monks


Pufferfish are among those few types of fish that positive exude personality; where fish like guppies and tetras may be attractive and alert, they don’t really give the impression of forming any particular bond with their owners beyond seeing them as a source of food. In contrast puffers, like many of the cichlids, seem much more aware of their surroundings, and as much as you watch them, they watch you. Pufferfish also score in the cuteness stakes as well, having expressive faces with large eyes and an unusual, bird-like beak.

It’s no surprise then that many newcomers to the fishkeeping hobby decide to buy a small pufferfish for their aquarium; but what is as a surprise to their owners is just how much trouble keeping pufferfish can be. Even though they may look friendly when young, adult pufferfish are often very aggressive towards one another, and they may even attack unrelated fish too slow to get out of the way. Some specimens are also confirmed fin-nippers, and will take chunks out of the fins of slow moving fish like gouramis and angelfish given the chance.

Complicating matters further is the fact that several so-called freshwater puffers are in fact brackish water fish, and will not do well in freshwater aquaria over the long term. However, there are also several species that do inhabit freshwaters for their entire lives, but not all aquarists or retailers seem to be aware of this, and you’ll often come across freshwater species being kept in brackish water.

No wonder then that puffers have tended to be branded as difficult fish best kept by advanced aquarists in a single-species tank. This is a bit of a shame, because there is actually quite a lot of variety in the pufferfish group, and some species make much nicer pets than others. The trick is to identify the species being sold in your aquarium before you spend any money. This is fine with the more distinctive species like the mbu puffer, Tetraodon mbu, and the Congo puffer, Tetraodon miurus, but what about those green spotted puffers that all seem to look alike?

Green spotted puffers, and how to tell them apart

There are at least five species of commonly traded pufferfish that are green and spotted, and all look rather similar at first glance. Even though they look alike, they are all very different fish as far as behaviour and required water conditions go, so being able to tell them apart is crucial. Generally speaking, you can expect your retailer to correctly label the South American puffer, milk spotted puffer, and figure eight puffer; the problem comes with the common and green spotted puffers, which are very similar indeed. The following species descriptions should help you identify the species available at your retailer, but note that the “distinguishing features” are for juveniles; adult pufferfish usually have the same markings but to a lesser degree, with the colours muted or the patterns faded. However, since it is juveniles that are normally offered for sale, it is those that we are interested in here.

South American Pufferfish, Colomesus psittacus

Distinguishing features: Apart from the beak, this fish has a rather flattened face. The body is white underneath with alternating green and black saddle-like patches along the back. Very active, and, unlike most other puffers, this fish is apt to be nervous.

A peaceful, freshwater pufferfish that will do well in a community tank along with quite fish of comparable size. Since this fish comes from the Amazon, it would fit in nicely in a South American community including plecs, pimelodid catfish, peaceful cichlids such as severums and acaras, and large characins like silver dollars. South American pufferfish are territorial, but in big tanks more than one specimen can be kept, and as youngsters being kept in small groups may help them settle in more quickly.

This pufferfish is one of the larger species, potentially being able to reach lengths of 25 cm, although they rarely do so in captivity. Part of the problem is that this species is quite delicate compared to most of the others, and needs well-filtered water with a high oxygen content. Making matters worse, the South American pufferfish is rather nervous, even hyperactive at times, and takes quite a while to settle into a new aquarium. It is a very active fish, and does not tolerate the confines of a small aquarium well, and should be kept in a tank no less than 100 cm in length.

The South American puffer is a bit particular about its food, and has a marked preference for live foods such as river shrimp and snails. This species is also notorious for its fast-growing teeth (see the tips on general care, below). The bottom line is that this species will not do well in an overstocked community tank, and is best avoided by inexperienced aquarists.

Milk Spotted Pufferfish, Chelonodon patoca

Distinguishing features: This fish is milk-white underneath with white spots and stripes on the top. There are also a few black, saddle-like marks on the back as well, particularly on the back half of the animal.

Although not a commonly seen species, the Asian and Australian milk spotted pufferfish is definitely worth looking out for if you want a robust, peaceful pufferfish for a big brackish water community tank. It would make an ideal companion for a school of scats and monos, posing no threat to such large, fast moving species. The milk spotted pufferfish could also work well with a small group of Colombian shark catfish. Even though it is sold as a freshwater or brackish water fish, this species will also thrive in a marine aquarium.

In many regards this fish is a lot like the South American pufferfish: it grows to about the same size, will only take live foods, and tends to be a bit nervous in captivity, at least to begin with. Also like the South American pufferfish, in a big enough aquarium a small group can be kept without problems.

Figure Eight Pufferfish, Tetraodon biocellatus

Distinguishing features: Essentially off-white underneath and green on top, this back of this fish bears has characteristic circular blotches of darker green edged with yellow. Often, these patches merge, forming the “figure eights” that give this fish its common name.

One of the most commonly traded pufferfish species, the figure eight pufferfish is an aggressive freshwater species that has been known to develop fin-nipping tendencies. As such, it cannot be recommended for the average community tank. Even in the best of conditions, these fish are hostile towards one another, developing a strict pecking order that often leaves the smaller and weaker individuals with scars on the body and pieces bitten out of the fins. In the close confines of the aquarium, dominant individuals are able to bully the other pufferfish to such a degree that they cannot feed, resulting in death by slow starvation.

This fish is at least fairly small, typically well under 10 cm in
length when mature, and so could be kept in a small, single species
tank without problems. It is quite adaptable, but despite being a
freshwater fish in the wild, in aquaria it appears to do best in
slightly brackish, alkaline water (a specific gravity of about 1.005
and a pH of 8 is ideal). Like other puffers, it is a greedy fish, and
will accept all sorts of live, frozen, and processed food although
snails and other shellfish should be a major part of its diet.

Figure eight puffers are found throughout South East Asia, and are frequently included in batches of oddballs from Thailand, Singapore, and Malaysia. Note also the Tetraodon steindachneri and Tetraodon palembangensis also go by the figure eight pufferfish name, and are most probably the same fish.

Common Spotted Pufferfish, Tetraodon fluvialitis

Distinguishing features: Off-white to grey underneath and yellowy-green above, this fish bears numerous small dark brown or black spots and patches on its back and sides. Unlike the figure eight puffer, these are not edged with yellow.

A fairly big pufferfish (around 15 cm being typical) that requires brackish water, the common spotted pufferfish is notorious for both its aggression and its tendency to fin nipping. Perversely, juveniles are among the most tolerant and peaceful of pufferfish, and many aquarists have taken this to suggest that they would make good additions to a community tank. As the pufferfish grow, they initially bully one another, usually forcing the aquarist to remove all but one specimen. In a very big tank, upwards of 120 cm in length, it may be possible to raise a pair of these fish, and perhaps even breed them (in a manner very like the cichlids, with the male guarding the eggs and fry), but generally speaking these fish are best kept individually.

The common spotted pufferfish is predatory and given to biting pieces from the fins and scales of larger fish. In a big tank (at least 100 cm long) it might be possible to keep an adult common spotted pufferfish with robust and fast-moving companions — the problem is that you cannot guarantee it. Even fish like monos and scats that would seem to be too fast for the clumsy puffer to molest sometimes fall prey, with the aquarist finding one the fish has a circular disc taken out of its fins.

Green Spotted Pufferfish, Tetraodon nigroviridis

Distinguishing features: Very similar to the common spotted pufferfish, except that there are no large saddles or blotches on the back.

In all regards this species is identical to the common spotted pufferfish. It is peaceful when young, territorial and aggressive when adult, and requires brackish, not freshwater, conditions. Many ichthyologists and aquarists consider the two species to be nothing more than geographical or morphological variations of the same fish, while others separate them out as distinct species. It doesn’t really matter very much for our purposes, since they require the same conditions in captivity.

General pufferfish care

All pufferfish have continually growing teeth that in the wild are ground down when the fish eats the crustaceans and molluscs that they hunt. In captivity puffers tend to be offered softer fare, with the result that their teeth are not worn down, and can become so long the fish cannot eat properly. Veterinarians can be called upon to file the teeth down manually, but it’s far better simply to ensure that the puffer is regularly given the hard, shelly foods that they have evolved to handle. Malayan livebearing snails are a very good option: they are easy to raise at home, and many aquarists and retailers even consider them a pest, so getting a ‘starter culture’ shouldn’t be hard!

There are a few other things that need to be help to keep puffers healthy and happy. The first is to ensure that the aquarium includes enough to amuse them, since these are naturally active, inquisitive fish. Many like to dig, so at least a patch of sand or fine gravel will be appreciated. A mixture of rocks, bogwood, and plants will add complexity to the aquarium and give them something to explore as well as somewhere to hide. All puffers are greedy, messy fish, so it’s important not to overfeed them and to ensure that you have a powerful filter that is up to the job. Finally, if you put a puffer into an established community tank, keep an eye out on for signs of fighting or fin nipping; wounds can quickly become infected with things like fungus and fin-rot.

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