Specimen of the Week: Week 107
By Emma-Louise Nicholls, on 28 October 2013
Last week we had an amazing set of activities at the Museum for our event Life Under the Waves, where visitors could touch a sawfish snout, stroke a dolphin and smell a triggerfish (maybe only I did the last one). To protect our specimens we place them on a soft foamy mat that cushions them against the hard surface of the table. After clearing the specimens away, I noticed that one of them had left a fascinating set of depressions in the foam. Highly amused by this, I tried to photograph it to share it with you, but it just looked like I’d taken a picture of a table. So, I will tell you about it instead. This week’s Specimen of the Week is:
**The porcupine fish**
1) What is the difference between a porcupinefish and a pufferfish? The difference is not made obvious in the general literature as most often they are clumped together. However, luckily for you, I did my homework. I can now reveal to you the ridiculously complex scientific method of differentiating between the two groups. Porcupine fish are spikey. Pufferfish are less so. There are many species of pufferfish and all have the ability to inflate themselves, but it is the inflated porcupinefish that looks like the unholy lovechild of Pinhead and a football.
2) This genus of porcupinefish, called Diodon, has around 20 spines in each row that run from the snout to the tail. It expands its body by rapidly taking in water. Although doing this makes them cumbersome in the water, their huge spines help enormously in their evasion of predators. When err, de-flated, the spines lay flush against the fish’s body.
3) The porcupinefish has strong jaws and fused teeth which create a beak-like mouth capable of cracking open the shells and carapaces of snails, hermit crabs, and sea urchins. Adult porcupinefish live solitary lives and are usually found sheltering around caves, reefs, and even shipwrecks. The juveniles however are far more outgoing, and live in the open ocean. Once they reach around 20 cm in length, they retire to the shelter of the reef with the other adults.
4) As the juveniles are such get-up-and-go fish, it is no wonder that the porcupinefish has a wide distribution. The small, spherical eggs drift around in the current for about five days after being laid, at which point they hatch into planktonic larvae but they lack a functional mouth. It is only after a few days that they start to resemble fish at which point they are as likely to get eaten by dolphins and billfishes as reach they adulthood.
5) Porcupinefish are shy and prefer to hide in a crevice that inflate. They are considered poisonous as they secrete a toxic substance through their skin that is harmful to humans. Despite this, humans of course found a way to eat them in some parts of the world. Due to their fantastic appearance, they are frequently sold on the tourist market as dried inflated curiosities. On some islands in the Pacific, the dried skins of porcupinefish were used as war helmets in the past.
Emma-Louise Nicholls is the Curatorial Assistant at the Grant Museum of Zoology