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Inside the mind of a puffer

Understanding pufferfish behaviour for better pufferfish husbandry

by Neale Monks

Pufferfish are among the most popular of all the oddball fish, and most aquarium stores carry at least one or two species. There is much about pufferfish that is fascinating, whether it is the fact that many species are highly poisonous through to their bizarre parrot-like beak. Some species do very well in aquaria, learning to recognise their owner and soon learn to beg for food. The figure-8 pufferfish, Tetraodon biocellatus, from South East Asia is perhaps the most commonly seen, but there are plenty of others, including species from Africa and South America. Pufferfish range in size from species over 60 cm when long when mature, like Tetraodon mbu, through to the dwarf species of Carinotetraodon no bigger than a small barb or tetra. Most aquarists are also aware that the puffers sold as freshwater fish sometimes need brackish water conditions to do best, particularly as they mature. The popular green spotted pufferfish, Tetraodon nigroviridis, is one such species, many aquarists having found that the adults will prosper in marine aquaria.

Size and water conditions are two of the key things to consider with any fish, but behaviour is something that is easy to overlook but just as important. Rather than hope that a fish will conform to your expectations as a community fish, puffers need to be worked around, and their rather particular habits anticipated.

The eyes have it

In this article, we'll try and see the world through the eyes of a pufferfish. In fact, the eyes are a great place to start our considerations. What makes puffers so charming and endearing even to non-aquarists are their large, mobile eyes. Pufferfish hunt almost entirely by sight, and their prey is often slow moving and well camouflaged, things like snails and shrimps. So where another predatory fish might simply wait for something to move and catch its eye, puffers need to explore their habitat carefully, studying the terrain closely to see if something that looks like a bit of rock or algae is in actual fact its prey.

Compared with most other fish, puffers seem to have very expressive faces, and it is this that makes them so popular. In reality, much of this is merely an accident of anatomy. Pufferfish have very large and powerful jaws, and to make room for the muscles that operate their jaws, the nostrils are on the outside of the head, usually just in front of the eyes. Likewise the eyes, rather than being recessed in the head as on most fish, bulge outwards more like those of a frog. They have fleshy lips that normally cover the beak except when the fish is feeding. The lips provide the pufferfish with useful information on the taste and texture of the object it is trying to eat. This helps the puffer decide if the thing is actually worth eating, and makes sure it doesn't waste energy on something inedible like an empty shell, or worse, accidentally break its teeth or jaws trying to break open something like a stone.

Finding food

All pufferfish are predators, but the way they get their food varies. Three main groups can be recognised: open water hunters, stealth predators, and ambush predators.

The open water hunters cruise over rocky and sandy substrates looking for potential prey. These species feed on things like oysters, clams, snails, shrimps, and crabs. As with all pufferfish, hunting is done by sight, but a particular characteristic of these types of pufferfish is their careful searching behaviour. When looking for food, these puffers will carefully swim up and down objects such as oyster beds, mangrove roots, or aquatic plants searching for potential prey. The hunt is carried out diligently and efficiently thanks to their excellent eyesight and their unique swimming mode. The way pufferfish swim compared with that of other fish is rather like comparing a helicopter to an aeroplane; while they may be slow, they are extremely manoeuvrable, and this allows pufferfish to spot and capture prey that other fish would simply swim straight by.

The majority of pufferfish fall are open water hunters, whether they are marine, brackish, or freshwater species. Like many other open water fish, these puffers are light grey or cream-coloured underneath and green above, making them less easy to see when swimming in open water. Many species also have a scattering of black spots or squiggles on the back and flanks further improves their camouflage by breaking up their outline, in the same way as the stripes on a zebra. Typical examples of this class of pufferfish are the golden puffer, Auriglobus modestus, and the South American puffer, Colomesus asellus. In aquaria, these open water fish need lots of space for swimming as well as a complex tangle of rocks, bogwood, and plants for them to explore.

The stealth predators feed on the same sorts of prey as the open water hunters, but for various reasons prefer not to swim out in the open. The crested puffer, Carinotetraodon lorteti, and the dwarf puffer, such as Carinotetraodon travancoricus, are typical stealth predators. Because they are so small, they are vulnerable to being eaten by larger fish, so they stay close to cover, and are only ever found in overgrown riverbanks and other places where there are lots of tree roots, plants, and other hiding places. An aquarium for these dwarf puffers would need to respect this, and should be thickly planted if you want these fish to settle in quickly. Swimming slowly through the undergrowth, these small puffers hunt for snails, mosquito larvae, water beetles, and other small invertebrates. One peculiarity with these puffers is the strong sexual dimorphism between the males and females. While the females invariably have some type of mottled colouration that provides excellent camouflage, the males are more brightly coloured. The red-tailed redeye puffer, Carinotetraodon irrubesco, for example, is coloured in exactly the way its common name suggests.

The final class of pufferfish is that of the ambush predator. Unlike the other types of pufferfish, which feed principally on invertebrates, these puffers eat fish. However, just like other pufferfish, they lack the speed to chase after their prey, so instead they hide in the sand and then lunge upwards at any fish that swim above them. Fortunately for the aquarist, there is no need to feed this pufferfish with live fish; it will take small frozen fish such as lancefish and whitebait at once, if they're dangled in front of the pufferfish in a tempting way. Eventually be weaned onto things like prawns, clams, and snails that they will take from off the substrate, something that doesn't come naturally to these fish given their upwards-pointing mouth. The chief example of this type of puffer is the Congo puffer, Tetraodon miurus. This puffer digs itself into the sand with only its eyes protruding, and then waits for a fish to swim overhead. In aquaria, use a silica or river sand substrate to provide these pufferfish with a soft substrate into which they can dig easily.

Psycho Puffers

Aggressive and territorial fishes, be they puffers or cichlids, are often thought of as simply psychopaths, wanting to do nothing more than spread mayhem and destruction across their immediate environment. While this may be fun to believe, it isn't good science, and it is far more useful to try and understand why a pufferfish might attack other fishes kept alongside it. The answer is obvious for species like Tetraodon miurus and Auriglobus modestus, puffers that feed either on whole fish or on their scales and fins; but for species that feed only on invertebrates, why would they attack other fish? One thing that can be ruled out is guarding a feeding ground in the way that many damselfish and surgeonfish do. Whereas those marine fish feed on algae that can be 'farmed' on a certain patch of rock, the clams and snails puffers prefer cannot be cultivated in any meaningful way because they grow too slowly. At best, a pufferfish can try and monopolise a particular bed of oysters or clams for a while, but eventually if will have eaten all the ones small enough to break open, and it'll have to move on to another patch of food.

In fact, many pufferfish are territorial for the same reasons as many cichlids. Since the males guard the eggs, they need to be able to clear their territory of and potential predators. Natural selection has favoured those males that drive away predators with the greatest success, since those males have been able to protect the most eggs, and so have passed on their genes most effectively. Males also need to hold their territories against rival males even before he has eggs to look after, since the best nesting sites are often in short supply. This works to advantage of the female when it comes to choosing a mate with the best genes: if she can find a male that can successfully defend his territory against his rivals, she can be sure that he has good genes. Simply being aggressive all the time is counter-productive though. There's no evolutionary advantage to picking fights outside of the breeding season if there's nothing worth fighting for. Hence, pufferfish that fight to protect their eggs or nesting sites do so most vigorously only at certain times of the year.

Among the species that are only aggressive when breeding are several species of the dwarf puffer genus Carinotetraodon. They are otherwise tolerant of one another most of the time and it is possible to keep these fish in groups. The key thing is not to overcrowd these fish; even though the are not looking for fights, if they are forced to live check-by-jowl, flare-ups will happen. Small species like Carinotetraodon travancoricus can be kept in groups with around five gallons or so allotted to each fish, and a pair of Carinotetraodon irrubesco will get along perfectly well in a ten- to twenty gallon aquarium. As well as tolerating conspecifics, these little puffers usually get along well with small, slow-moving, non-threatening tankmates such as Otocinclus catfish and gobies. Making sure there are lots of places to hide is important, not only for the pufferfish, but also for the tankmates. Any territoriality from these pufferfish is usually short-lived, and so if the other fish can get out of the line of sight, things normally settle back down again very quickly.

The figure-8 puffer, Tetraodon biocellatus, is another species that can be kept in groups, though being rather larger than Carinotetraodon species the aquarist does need to provide a bit more space, something around 10 to 15 gallons per fish being about right. Other species that cohabit peacefully with their own kind include Colomesus asellus, Tetraodon fluviatilis, and Tetraodon nigroviridis, though with the last two species especially account does need to be made for their relatively large adult size. It would be unwise to keep more than one specimen in an aquarium of less than 55 gallons.

There are some puffers though that hold such large territories, and seem to do so even when not spawning, that keeping them in groups is practically impossible in home aquaria. Tetraodon lineatus (commonly referred to in the hobby as Tetraodon fahaka) is a famous example of this, and it simply cannot be kept in an aquarium with any other fish. Indeed, it will even attack the arm of any aquarist foolish enough to work in the aquarium without first pinning the pufferfish back with a net. Other pufferfish that cannot be kept in groups include all the traded species of Auriglobus and Chonerhinos, Tetraodon miurus, and the brackish to marine species Arothron hispidus.

Of fin nipping and boredom

Some pufferfish are known to be semi-parasitic, that is, supplementing their regular diet of snails and shrimps they will also eat the scales and fins of larger fish. This behaviour, also observed in many barbs and tetras as well, can be very troublesome for the aquarist. Among the species known to be persistent fin-nippers are the milk-spotted puffer, Chelonodon patoca, and all the traded species of Auriglobus and Chonerhinos.

On the other hand, the majority of puffers seem to be opportunistic fin-nippers, and do so only under certain circumstances. The South American pufferfish, Colomesus asellus, for example, only seems to go for slow moving species such as Corydoras, fancy livebearers, and gobies. Provided it is kept with more active fish such as tetras, halfbeaks, and hatchetfish, it is entirely trustworthy. Remember the sensitive lips mentioned earlier on in this article? For a hungry pufferfish, the way to see if something is edible is to have a bit of a nibble. Obviously nibbling on a rock does no harm, but if the pufferfish is trying out a bit of Corydoras, then the results aren't so good.

As mentioned earlier on, most puffers have evolved to explore complex environments while searching for food. Whether it is this that makes them so intelligent is an interesting point for debate, but certainly pufferfish kept in empty or thinly decorated aquaria show all the classic signs of boredom: listlessness, destructive behaviour, and seemingly random aggression. Pufferfish need to be stimulated, and providing them with an aquarium that demands exploration will do this. Use lots of rocks, wood, and plants to create an aquarium that isn't an empty box but one filled with caves and structures. You will then be able to watch your pufferfish behaving naturally, searching every inch of its surroundings for potential prey. Floating plants are particularly valuable in aquarium containing the open water species, providing them with interesting places to explore not just at the bottom of the tank but at the top as well. Most puffers seem to enjoy sandy substrates, either completely burying themselves under the sand or at least rooting about in it looking for snails. In short, the more in the aquarium for the pufferfish to 'play' with, the less likely it is to develop any bad habits.

Pufferfish are not the thugs of popular legend, but fish with very specific needs that too many aquarists fail to consider. While it is probably true that none are perfect community fish like neon tetras or Corydoras catfish, only a relatively small number are so aggressive that they have to be kept singly. They are intelligent and need constant stimulation, and whether that is by creating a complex habitat or providing suitable tankmates, keeping pufferfish properly is a challenge, but one that is ultimately very rewarding.

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