“ET phone home.” That famous movie phrase comes to mind every time I come to face-to-face with a balloonfish, also known as the longspine porcupinefish. Its large head and big eyes give it an alienlike appearance. The balloonfish is also a fish full of personality. In fact, it has more charm than a lot of the people I have met during my travels through life! But this ocean-bound ET is not suitable for everyone.
Difficulty: The balloonfish can be an easy fish to keep once you convince it to eat aquarium fare. Most individuals, in time, will greedily accept chopped seafood, frozen krill and frozen preparations for marine carnivores. If you feed the balloonfish a varied diet, at least once a day, it will stay happy and healthy and could live more than a decade in your aquarium.
Physical description: The balloonfish has a bulbous head and a short tail. The body is covered with sharp spines that lay backwards until it inflates with water. The balloonfish inflates in this manner when threatened by predators. (On occasion, you may see this fish inflate for no apparent reason as if practicing for those times when inflating might save its life!)
Diodon holocanthus has large spots scattered about its light brown body and darker saddles. The balloonfish reaches a length of about 15 inches. Its larger cousin D. hystrix (known simply as the porcupinefish) reaches a massive 28 inches in length. It is a more elongate Diodon sp. that has numerous small spots (much smaller than the size of the eye) all over its body and tail.
Range: The balloonfish has a circumglobal distribution. It is found at depths from a couple of feet to 330 feet. While porcupinefish can be seen on coral reefs, they are more abundant in adjacent habitats, such as open sand plains, around pier pilings or on rubble slopes. During the day they are quiescent, but at night they come out to wreak havoc on the nocturnal invertebrate community. Diodon holocanthus uses its fused teeth (which form a beaklike dental plate) to crush the shells of snails, bivalves and hermit crabs. Even the spine-studded tests of sea urchins does not dissuade hungry porcupinefish (urchins are its favorite food)!
Compatibility: Balloonfish rarely cause problems in a community aquarium with large fish. You should never keep the balloonfish with sedentary ambush predators (e.g., bamboo sharks, wobbegongs, frogfish, scorpionfish, etc.), as they may decide that these fish are good to chew on. Diodon holocanthus also eats seahorses and pipefish like hard candy and may occasionally nip the fins of species with long, flowing fins (e.g., batfish). Otherwise, they rarely mess with their fish neighbors.
There are only a few fish that could cause problems for your balloonfish. One of these is the longfin bannerfish (Heniochus acuminatus). Adults have been known to persistently pick at porcupinefish and pufferfish causing tissue damage and eventual death. Groupers may also try to eat small juveniles — there’s been more than one case of a frogfish or a grouper having had an inflated Diodon lodged in its mouth or gullet! While it can be kept with live corals, say goodbye to snails (including cowries), ornamental crustaceans and echinoderms (i.e., sea stars and urchins).
Aquarium conditions: The aquarium of the balloonfish should be large — a 75-gallon aquarium or larger is best. Make sure to provide your balloonfish with some good hiding places, although they spend little time under cover once they acclimate. Instead, they regularly have their snouts plastered against the glass looking for their food providers.
If you have an acrylic aquarium, be aware that some balloonfish have been known to bite and cause scratches on the acrylic with their hard beaklike teeth. For a fish with teeth that can crush sea urchins and mollusk shells, scratching plastic is not that great a feat. Acceptable water parameters for the balloonfish are a pH of 8.1 to 8.4, specific gravity of 1.019 to 1.025 and a water temperature of 74 to 82 degrees Fahrenheit.
Care considerations: One thing to keep in mind is that balloonfish are very prone to diseases, often breaking out with Cryptocaryon at the drop of a hat. Apparently, the balloonfish can even harbor the cysts of this parasite, in a dormant state, in their internal organs. But if you drop the specific gravity for several weeks (to around 1.012), they should recover. One thing you should never do is to encourage your balloonfish to inflate. This causes the fish stress, and if it should ingest air it may have a difficult time belching it out. Hopefully, the balloonfish will work it all, but there’s nothing the hobbyist can do in such circumstances.
Breeding: The balloonfish is not likely to spawn in the home aquarium. Reproduction in this species is quite violent, with males biting females during spawning.