Diodontids: At a Glance
There are diodontids in all warm, temperate tropical seas, and some are wide-ranging in their distribution. In fact, the longspined porcupinefish (Diodon holocanthus) and its big cousin, the porcupinefish (Diodon hystrix), are found in tropical coastal habitats all around the world. One reason that they are so common is because of the long pelagic phase of their life cycle. When spawning occurs, the eggs are swept off the reef into the open ocean where they develop and hatch. There the young fish feed and grow. In most coral reef fish, the young fish are very small (less than an inch) when they finally “settle out” of the plankton and begin their life near the sea floor. But in the diodontids, the young fish remain within the plankton for a longer period and are quite large upon settling out onto the reef. In fact, some species (e.g., spotted burrfish, Chilomycterus reticulates) can be as large as 8 inches when the planktonic phase of the life cycle ends.
With their box-shaped bodies and small tails, these fishes are by no means oceanic speedsters. In fact, they have a somewhat unique swimming style called the diodontiform mode of locomotion. This involves undulating the edges of their broad pectoral fins, along with oscillating the median fins. This way of getting around allows for fine changes in position (something that helps when trying to locate and capture prey) but does not allow for great speed. Fortunately for the diodontids, they do not rely on speed to avoid generalized fish-eaters. Instead, their ability to inflate and the spines on the body make them an undesirable meal for most predators. They also have toxins in some of their internal organs and skin. But even with these defenses, the spiny puffers are eaten by some piscivores, including sharks (tiger sharks really love them), frogfishes, trumpetfishes, groupers, snappers and barracuda. This is not without some risk, however. For example, there is a report of a dead giant frogfish (Antennarius commerson) with an inflated balloonfish in its stomach that was found floating at the ocean surface and groupers with inflated porcupinefish lodged in their jaws. Apparently, the porcupinefish can inflate after being eaten.
While habitat preference is in part a function of the species of spiny puffer in question, in many regions, the diodontids tend to prefer less pristine marine habitats. For example, longspined porcupinefish (D. holocanthus) often prefer turbid, coastal habitats where they can be found living on low-profile reefs, around pier pilings or among manmade debris (i.e., trash). They are sometimes found on small patches of debris on sand or mud flats or slopes. That said, in other regions, the wide-ranging D. holocanthus occurs on well-developed coral reefs. There is at least one species, D. eydouxi, that spends its entire life living in the open ocean (i.e., it lives a pelagic lifestyle).