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| Big Biters: Triggerfish and Pufferfish |
| 14/02/2007 |
Though marine aquarists often focus on reef tanks that combine fishes with invertebrates, there's lots of fun to be had with fish-only systems as well. The order Tetraodontiformes includes five families that make very interesting and worthwhile additions to a fish-only marine aquarium, the Balistidae (triggerfishes), Monacanthidae (filefishes or leatherjackets), Diodontidae (porcupinefishes), Ostraciidae (boxfishes), and Tetraodontidae (pufferfishes). Although each is distinct in its way, all five families have a good deal in common, both in terms of morphology and in mode of life. On the other hand, each does have its quirks, and not all are equally adaptable or robust under aquarium conditions. For this reason, while it is certainly useful to consider them as a group, it is also important to look at the particular needs of each family before selecting which one is right for your tank.
General biology
As a group, the Tetraodontiformes are characterised by a suite of adaptations that allow them to feed on well-hidden, camouflaged, or heavily armoured prey that other fishes cannot eat. Specifically, all are equipped with excellent eyesight that helps them find their prey. The eyes are often mobile and rather chameleon-like in being able to move independently. To enable them to search their environment more carefully, these fishes swim slowly but efficiently, propelling themselves with undulations of the dorsal, anal, and (in some cases) pectoral fins. If the tail fin is used for swimming at all, it is only used for emergency bursts of speed. Once they have located their prey, they use their extraordinarily powerful jaw muscles to extract the prey from its hiding place and then to break open its shell or exoskeleton. Compared with other fishes, the Tetraodontiformes show a tendency towards a reduction in the number of teeth. Triggerfish have sixteen, very sharp, canine-like teeth, while puffers and porcupinefishes have four and two teeth respectively fused into a beak-like structure. All the Tetraodontiformes feed primarily on shelled invertebrates, such as shrimps, crabs, snails, clams, and so on.
In terms of behaviour, there is a fair amount of variation, but on the whole these are territorial, aggressive fishes that work best in single-species tanks either alone or with similarly robust tankmates. For the most part they cannot be kept in reef tanks because they simply view things like shrimps and corals as food. However, because these fishes are naturally curious and enquiring animals used to exploring their environment and learning to handle new types of prey, they are also make intelligent and rewarding pets. Many species become tame very easily and may even be hand fed, though given the strength of their jaws, it is best to do this holding the food with tongs or forceps rather than your fingers!
Triggerfish and filefish
Triggers and filefish are very similar in basic shape, and the differences between them are chiefly anatomical and of no particular interest to aquarists. Both have deep, laterally compressed bodies and swim using their dorsal and anal fins. If threatened, both will zip away from danger using their tail fin, and then wedge themselves into a crevice using a modified spine in the dorsal fin. On the whole, both can be characterised as being hardy and not particularly difficult to keep, though there are exceptions. Triggerfish especially have a reputation for being as close to bombproof as any marine fish, and many species live for ten years or more in captivity. As far as the aquarist is concerned, the chief differences between the triggers and filefish are size and personality. Though there are big filefish in the wild, the species offered to aquarists tend to be rather small and delicately built compared with the large and rather robust triggerfishes commonly on sale. Filefish are also rather shy and easily alarmed, whereas triggerfish tend to be outgoing and quick to settle into aquarium life. Filefish are often said to be less territorial amongst themselves than triggerfish, and to some extent that is true, but filefish can be aggressive and they are best kept one to a tank, just like triggers. Most filefish and triggerfish can be kept in community tanks, though some triggerfish at least are so territorial they are best kept alone.
The blue (or black) trigger Odonus niger is one of the most widely sold species in the aquarium trade. It is easily recognised thanks to its deep purple-blue colouration and distinctive red teeth. Normally sold at a fairly small size (around 8 to 15 cm) this is one of the larger triggerfish and in the wild can reach a length of 50 cm. Aquarium specimens regularly reach 30 cm, so plan ahead if you want to keep this fish and get as large a tank as possible. Its natural diet is quite varied, ranging from zooplankton through to sponges, and in aquaria it seems to be equally adaptable, eating pretty much anything. Shrimps, mussels, strips of squid, and other meaty foods are all enjoyed. By triggerfish standards this species is relatively peaceful and has been kept in community tanks alongside other robust species such as lionfish, pufferfish, groupers, and moray eels. In the wild, this species lives in schools, but within the confines of the aquarium keeping more than one specimen in a tank is not a good idea.
Another widely sold triggerfish is the Picasso trigger Rhinecanthus aculeatus. These are often sold as very appealing babies around 5 cm in length, and these grow only slowly, a few centimetres a year, until they reach a maximum size of 25 cm or so. In terms of behaviour, they are a little more aggressive than blue triggers, though their smaller size does at least mean they are at least easier to house properly. What really sells this fish is its amazing colours, a mix of yellow, blue, brown, and white against a cream-coloured background. A similar species, Rhinecanthus rectangulus, is also regularly offered for sale, and can be distinguished by a dark brown rectangular patch running obliquely from behind the eye to the base of the anal fin. There is a triangular patch of similar colour on the caudal peduncle as well.
Perhaps the most beautiful of all the triggerfish is the clown trigger Balistoides conspicillum. This is a large species similar in size to the blue trigger, but dark brown and covered with large white patches across the face and lower half of the flanks. There are yellow markings on the lips, face, and the top half of the body. This is one of the the most aggressive of all the triggerfishes kept by aquarists, and there are many reports of fishkeepers being bitten by this species. Certainly maintenance of the aquarium should be undertaken with care, with the triggerfish confined to one end of the tank with a net or divider. Otherwise not difficult to keep, though its nasty temperament rules it out for use in a community tank. Often as mean-tempered is the orange-lined trigger Balistapus undulatus, a beautiful but territorial fish that is really only viable in its own aquarium away from other fishes. Reaching a length of 30 cm at most, this species is quite commonly sold and extraordinarily hardy, making it an excellent choice for the aquarist lacking in experience of marine fishes generally.
Among the more mellow triggerfishes is Melichthys vidua, the pink-tailed triggerfish. Though certainly not reef-safe, this species gets along well with things like scorpionfish, angelfish, wrasse, etc. A subtle beauty, these fish are variable but typically have an olive-coloured body and a rose-pink tail. The pink-tailed trigger reaches between 30-40 cm in length and has a very catholic diet including algae, sponges, shrimps, and small fish. Species of the genus Sufflamen are less commonly traded but are both small (up to 30 cm, but typically less) and relatively gentle, sometimes even working well in reef tanks because they feed primarily on zooplankton, not benthic invertebrates.
Not as many filefish are offered for sale to aquarists as triggerfish, but a few species do regularly turn up. The very attractive long-nose (or orange-spotted) filefish Oxymonacanthus longirostris is perhaps the one species traded that is best avoided; in the wild this species and other members of its genus feed primarily on coral polyps, and getting aquarium specimens to feed successfully on other foods is not easy. To have any chance of success, the aquarist needs to keep this species in a very peaceful aquarium (no territorial damsels!) and provide regular meals of appropriately sized live and frozen foods. Most of the other species are much more easily maintained and will eat small shrimps, mysids, brine shrimp, chopped clams and mussels, etc. Probably the most regularly seen filefish is the tasselled filefish Chaetodermis pencilligera. Usually sold as a youngster around 5-10 cm long, adults grow to about 20 cm or so in captivity, a bit larger in the wild. This species is easily recognised by their rhomboid shape, squiggly black markings, and the feathery tassels all over the body. Although they will eat shrimps, snails, and any other invertebrates they can overpower, they are otherwise peaceful and can work very well in quiet fish-only communities.
Boxfish
Boxfish are somewhat like pufferfish in outline but have a more boxy shape thanks to the fusion of plate-like scales into a rigid box. Besides having this armour plating, boxfish are notable for being able to secrete a toxin when alarmed; in the aquarium it is possible for this toxin to kill all the fish in the tank (including the boxfish). For this reason, while these fish are interesting and attractive, they are definitely not for beginners. Above all else they must not be alarmed, and any tankmates should be completely peaceful. It goes without saying that if they get stressed while being transported they can poison themselves in the bag. Compared with the other Tetraodontiformes, boxfish tend to take smaller prey, and have a great fondness for things like bloodworms and brine shrimp, either live or frozen. Besides small invertebrates, they need green foods too, especially algae. They are rather slow feeders and poor swimmers, and easily starve if they have to compete with other species at feeding time. There's a good argument to keeping a single specimen in its own tank with only living rock and hardy, inoffensive invertebrates like turbo snails. They might also be kept with fish that feed also very slowly, such as seahorses or mandarinfish.
Lactoria cornuta is the longhorn cowfish, usually sold as tiny (~1-2 cm long) bright yellow box-shaped beasties that seems to hover and buzz around the aquarium like miniature helicopters. Adults reach up to 40 cm in length. As they grow, they develop long spines at some of the corners of the 'box', with the ones at the front looking vaguely like the horns of a cow, hence the common name. Various Ostracion spp. are also quite commonly traded. Ostracion cubicus is a typical example, often being sold as an almost cubic juvenile a centimetre or two across and bright yellow with dark blue-black spots. As it matures it becomes more elongate and the colours change, the yellow fading somewhat and the black spots become more spread out and interspersed with patches of white.
Porcupinefish
Essentially similar to pufferfish in overall shape and habits, porcupinefish are covered in spines, which puffers lack, and have a beak consisting of two teeth, rather than four teeth as is the case with puffers. But in most other regards these can be treated as similar sized pufferfish. They are hardy, adaptable, and willingly eat most hearty invertebrates. The most commonly traded species is Diodon holacanthus, an appealing but unfortunately rather large fish. Typically sold at about 12-15 cm in length, adults can easily exceed 40 cm, so be prepared to give this fish a big aquarium with lots of swimming space. In terms of temperament it is basically peaceful but it it will eat any and all invertebrates, not to mention smaller fish, and its sheer size and remarkable greediness make it only suitable for tanks alongside other robust fishes of similar size, such as snappers, lionfish, morays, etc.
Like pufferfish, porcupinefish have teeth that grow quite rapidly. In the wild, these are worn down by the types of food they eat, but in aquaria, where they are often given "soft" foods such as frozen prawns and squid, these teeth can become overgrown. To keep your porcupinefish in tip-top health, ensure that it is regularly given unshelled foods. Snails, clams, mussels, etc. are all ideal. While it is certainly possible to trim the teeth back manually, prevention is better than cure!
Pufferfish
Marine pufferfishes can be divided into two groups, the larger "true" puffers, typically Arothron spp., and the smaller "sharp-nosed" puffers or tobies, Canthigaster spp. The "true" puffers are generally hardy, entertaining fish that make excellent pets being quick to learn and very adaptable. The dog-faced puffer Arothron hispidus is a typical example. This species is sometimes sold as a brackish water fish and very rarely as a freshwater fish, and this reflects its wide range of natural habitats, ranging from estuaries (particularly as a juvenile) through to coral reefs. It gets to about 30 cm in length and is essentially peaceful, working well in fish-only aquaria alongside species of similar size, such as tangs, angels, lionfish, and so on.. In brackish water systems it can work well with monos, scats, and other large, fast-moving species. It is aggressive towards its own kind, particularly if overcrowded. Although not a colourful fish, it is an attractive fish nonetheless. Other species of Arothron will also be seen, and these vary in terms of colours and temperament. Arothron nigropunctatus is generally pretty placid and can work well even with fairly gentle marines such as tangs and angels. Arothron manilensis is a very attractive species that also works well in most fish-only aquaria.
Other genera of "true" pufferfish are not all that commonly sold, with the notable exception of various Takifugu that have been appearing in British aquarium stores in the last few years. A variety of subtropical and tropical species seem to be on offer, most frequently Takifugu ocellatus, a subtropical estuarine species with a green body and bright orange and black markings. Usually sold as a freshwater fish, it will do better in cool brackish water or marine conditions. Because it cannot tolerate tropical temperatures for long, its value to the average marine aquarist is negligible, but for the pufferfish enthusiast willing to provide it with its own subtropical aquarium, this beautiful fish would be an interesting challenge.
The "sharp-nosed" puffers are small (typically around 10-12 cm) pufferfishes with long snouts and a rather streamlined bodies. Canthigaster valentini is a typical and widely traded example. It is white with brown, saddle-like markings across the back and flanks. The eyes and tail fin are yellow. Canthigaster solandri is another commonly seen species with a reddish body covered with neon blue spots and squiggles. Sharp-nosed puffers are generally easy going animals but many are confirmed fin-nippers and so should be kept only with fishes able to swim away, hide in crevices, or otherwise defend themselves. On the other hand, don't mix a sharp-nosed puffer with overtly aggressive tankmates such as triggerfish or very territorial damsels. Like other puffers, they are antagonistic towards one another, so keep one to a tank. Their usefulness in reef tanks is debatable. Some aquarists have good luck keeping them in a tank with living rock and robust invertebrates such as cleaner shrimps, turbo snails, starfish, etc. Sharp-nosed puffers nibble away at all sorts of sessile invertebrates and can damage corals and other cnidarians in the process. They also eat some algae, and providing them with algae-based food items is probably a good idea.
Conclusion
Triggers, puffers, and their allies provide the marine aquarist with lots of species eminently suitable for the home aquarium. By marine fish standards, most are hardy, but this shouldn't be taken as an excuse to neglect water quality. These are all messy, greedy fish and filtration should be generous and water changes frequent. So while at least some of these fish can be considered good for newcomers to the marine side of the fishkeeping hobby, researching your fish before purchase and diligent husbandry afterwards are both essential. Beyond that though, triggers and puffers represent a high point as far as intelligence and personality go, and these can be become real pets in the sense of engaging with their owner and providing entertainment and companionship.
Learning more
Most marine aquarium books will cover the key topics like water quality and filtration, and any book about marine aquarium fishes will include some of the species mentioned here. The Aqualog pufferfish book is also worth reading; though written for aquarists keeping them in freshwater and marine tanks, it includes detailed information on many marine species as well as lots of advice on keeping pufferfish generally.
Marine Fish by Herbert Axelrod and Warren Burgess
Aqualog - The Puffers of fresh and brackish waters
This article cannot be reproduced without the permission of Tropicalfishfinder.
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