When is a porcupine not a porcupine?

I do like a nice corpse. You can get up close to see intimate details and not worry about disturbing an animal. Of course, it’s sad to see something dead, but that’s life (or not).

After a storm at Lighthouse Beach, Ballina, we trawled the waterline to see what had washed up, as is our wont. One of those things turned out to be the remains of a porcupinefish.

Turning it over revealed …

In amongst the wreckage was the jawbone, both top and bottom. The Beast tells us:

They feed nocturnally on hard-shelled invertebrates like crabs, clams, mussels and sea urchins. Their teeth are fused together into a plate, which enables them to crush through the hard shells. This also gives their mouth that beak-like appearance. Porcupine fish have thick, rubbery lips to protect them from the spines and broken shells of the prey they eat.

Startled porcupine fish suck in air or water to inflate their bodies, becoming a prickly balloon-like shape to defend themselves from predators and some contain a neurotoxin a thousand times more potent than cyanide in their ovaries and livers. They are also good at offense, crushing the shells of clams and other marine mollusks …

(From https://phys.org/news/2017-08-jaws-porcupine-fish-reveals-species.html)

You can also see a photo of a ‘blown-up’ porcupinefish at The Beast .

I contacted the Queensland Museum, who kindly allowed me to use their photo (below) of the spines and jaw of the threebar porcupinefish, Dicotylichtys punctulatus. They are very similar to those of my corpse, and the threebar has been found from southern Queensland to northern Tasmania, so the distribution is right for Ballina.

Threebar porcupinefish, Dicotylichthys punctulatus, jaw and spines (photographer Jeff Wright; reproduced with permission from the Queensland Museum)

The Australian Museum says:

The species is found on coastal and offshore reefs, often in rocky areas. … Porcupinefishes in general feed on invertebrates. … The teeth are fused to form a single plate in both jaws. … The flesh is reported to be poisonous but the spines are not toxic.

One thing that didn’t come with my corpse was the gas or swim bladder.

The gas bladder (also called a swim bladder) is a flexible-walled, gas-filled sac located in the dorsal portion of body cavity. It controls the fish’s buoyancy and in some species is important for hearing. Most of the gas bladder is not permeable to gases, because it is poorly vascularised (has few blood vessels) and is lined with sheets of guanine crystals.

The Queensland Museum says:

Although many fishes have swim-bladders they are generally soft and decay quickly, whereas those of the porcupinefish are very tough and survive for a long time after the fish has died. In life when agitated the porcupinefish can inflate its body and wedge itself into the reef, making it nearly impossible to swallow by a predator.

Swim bladder of porcupine fish, Diodon sp. (photographer Jeff Wright; reproduced with permission from the Queensland Museum)

Assuming my corpse is that of the threebar porcupinefish, it would have looked something like this in life.

Three-bar porcupinefish (Dicotylichthys punctulatus) (photographer Richard Ling, Wikimedia Commons)

So the answer to the question posed by the headline is: when it’s a fish!

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2 Responses to When is a porcupine not a porcupine?

  1. Kathy Pearce says:

    So interesting – than you!

    I looked at the Lord Howe shell link. Such great photos.

    Reminds me of the giant clams we saw snorkelling at the Frankland Islands, off Tully. I could fit my arm, or lower leg in one.

    But the little ones you show are so cute.


  2. janebeau says:

    Here we call all varieties of these “blaasoppies” or blow-ups.

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