Posted by: Rob Viens | March 8, 2012

Prodding a Porcupinefish

On March 8th Darwin was still in a hammock, gazing through the skylight at the clouds and trying to block out his pain. But his miserable week was broken up by an encounter with a unique fish:

“This fish, with its flabby skin, is well known to possess the singular power of distending itself into a nearly spherical form. ” (Voyage of the Beagle)

From the description it is pretty clear that this was a porcupine fish (or blowfish).  It’s not clear exactly when this happened (it does not appear in his diary), but since the encounter was off the ship I suspect that it was during the week he was stuck on board. Darwin found this particular fish to be so fascinating that his description of the encounter takes up almost half of the “Bahia” section in Voyage.

Chilomycterus antennatus – a type of blowfish (from Fishbase):

Bridled Burrfish

Porcupinefish belong to a order of fish known as the Tetraodontiforms, which also includes triggerfish, ocean sunfish, boxfish, and pufferfish. Many of the more than 350 species of this fish are found in tropical water around coral refers (though there are always exceptions to general rules like this). Most of the tetraodontiforms are slow moving, and therefore defend themselves from predators with thick scales and spines, or by secreting tetrodotoxin – a potentially lethal neurotoxin.  This is the neurotoxin that makes eating fugu (aka pufferfish) potentially hazardous to your health. It is estimated that a mere 25 milligrams of this toxin would kill a 170 pound person. Interestingly, pufferfish that are raised in captivity do not produce the toxin, which suggests that it accumulates in their system from the food they eat.

The porcupinefish (Diodontidae) and pufferfish (Tetraodontidae) families also have the ability to “inflate” (or puff up) their bodies into a spherical shape. Their family names reflect one of their differences – the number of teeth-like bones the fish have (two vs. four). Another difference is somewhat evident in their names – the porcupinefish have larger “spikes” that stand up when they inflate.

Chilomycterus antennatus on a postage stamp (from Fishbase):

Bridled Burrfish

Darwin calls the fish he observed a Diodon antennatus. Unfortunately, this name is no longer used today, so the exact species Darwin described is hard to pinpoint (especially for someone like myself who is not an expert on tropical fish – or any fish for that matter). Identification guides note that Diodon antennatus is now classifified as Chilomycterus antennatus (the bridled burrfish). It is possible that this is the fish Darwin saw, though according to distribution maps C. antennatus is not common in the area around Salvador. So it is entirely possible that Darwin was observing another type of porcupinefish.

He spends some time describing the mechanics of how the porcupinefish works. For example:

“The fish, having remained in this distended state for a short time, generally expelled the air and water with considerable force from the branchial apertures and mouth. It could emit, at will, a certain portion of the water; and it appears, therefore, probable that this fluid is taken in partly for the sake of regulating its specific gravity.” (Voyage of the Beagle)

I can almost see him putting the fish in the water, taking it out, poking it, etc. – trying to uncover all its secrets. (I hope he didn’t decide to taste it!) All this prodding revealed a another unique feature of the “Diodon”:

“it secretes from the skin of its belly, when handled, a most beautiful carmine-red fibrous matter, which stains ivory and paper in so permanent a manner, that the tint is retained with all its brightness to the present day: I am quite ignorant of the nature and use of this secretion.” (Voyage of the Beagle)

Interesting – I thought this might narrow down the ID of this particular fish, but with limited resources it took me no closer to the truth.

Darwin’s encounters with unusual creatures (such as the cuttlefish in St. Jago –see Colorful Corals and Cuttlefish) are always enjoyable to read.  His sheer fascination with their newness, his descriptions of their unique traits, and his quest to test and observe their special “skills” is refreshing and inspiring.  It seems that one of his great strengths was to never loose the ability to be fascinated by the little details of the living things he observed.

Darwin’s final thoughts regarding this little blowfish speak to its power (and possibly toxicity):

“I have heard from Dr. Allan of Forres, that he has frequently found a Diodon, floating alive and distended, in the stomach of the shark; and that on several occasions he has known it eat its way, not only through the coats of the stomach, but through the sides of the monster, which has thus been killed. Who would ever have imagined that a little soft fish could have destroyed the great and savage shark?” (Voyage of the Beagle)

Sounds sort of like one man taking on the “monster” of the establishment.  Metaphoric foreshadowing perhaps? (RJV)

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Responses

  1. Beware of porcupine fish, you administrators! xox & happy birthday! 🙂

  2. I expect a meditation on Darwin’s birthday, Rob Viens birthday, perhaps the way porcupine fish are born…. Loved this post.


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