The Spiny Puffer's Message: You can't touch this!


Spiny Balloonfish (Diodon holocanthus)
Spiny Balloonfish (Diodon holocanthus)
by B. N. Sullivan

You can't touch this... and you definitely can't swallow it!

That is the message that fishes in the Spiny Puffer family attempt to transmit to potential predators.  While other creatures defend themselves from predators by fleeing, or hiding, or with camouflage, members of this family (Diodontidae) inflate themselves.  In addition, evolution has armed these guys with another feature: rigid spines all over their bodies that are erected when the fish inflates.

The Spiny Puffer's spines actually are like specialized scales. When the puffer is not inflated, most of the spines lie more or less flat against the skin, but when the skin stretches during inflation, the spines go upright.

Ain't nobody gonna swallow these babies!

Puffers are not very streamlined even when they are not inflated, so they are not fast swimmers.  Once they inflate they really are ungainly.  Their little pectoral fins will flutter, but they don't attain much in the way of forward motion.  To survive, they rely entirely on making themselves look unappealing as prey.

When a Spiny Puffer is molested or feels threatened, it opens its mouth and draws sea water into its stomach.  The stomach is capable of expanding greatly -- so greatly that the stomach and its watery contents can virtually fill the whole fish, squishing the rest of its organs up against its backbone.  Its skin is stretchy, too, which also helps it to expand like a balloon.

Both fish pictured in this post are partially inflated.   Each was pottering along in a shallow reef area when we spotted them.   In each case, Jerry shined his light on the fish so that I could approach and aim the camera for a close-up of the Puffer's cute face and interesting eyes.  But these are touchy critters, and that was enough to induce them to begin to inflate, so in each instance I snapped two frames and retreated before they freaked out.

Some divers intentionally harass or even try to grab puffers, just to see them inflate.  This is quite a mean thing to do.  Remember, inflation is a defense.  If the fish begins to inflate, that means it is alarmed.  If it puffs out to its maximum, it is really scared!  This behavior may be amusing to divers, but it really stresses the poor fish.

If you see a puffer and it begins to inflate, move away from it to let it know you are not a threat.  Don't terrorize the puffers!


Spotted porcupinefish (Diodon hystrix)
Spotted  Porcupinefish (Diodon hystrix)
Both of the Spiny Puffers on this page are Caribbean species.  I photographed them on two separate night dives in the Cayman Islands.  To give you an idea of their size, each of these individuals was approximately 12-14 inches (30-35 cm) in length.

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Bobbie & Jerry

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