Infrequent imports with a toxic surprise might not seem the most alluring of proposals, but Chris Sergeant thinks you might really want to get some soap in your tank.
YOU CAN INFER a lot from a fish’s common name. More often than not, morphology plays a key part in earning them their particular moniker. It may boil down to a physical characteristic, as with the longnose butterflyfish, Forcipiger flavissimus, scissortail sergeant, Abudefduf sexfasciatus, or the rostral protuberances of the unicornfish, Naso sp. It can be their resemblance to another creature, as with frogfish, Antennarius sp., or crocodilefish, Cymbacephalus beauforti. For others, like grunts, drums and croakers, their vocal capabilities mean it’s very much a case of say what you hear.
With that in mind, it doesn’t take much investigation to find out how soapfish got their name. Pick one up or stroke its skin and, just like rubbing a bar of soap, the fish begins to lather up. But, what’s the purpose of this you may ask?
Close encounters of the worst kind
On the reef, soapfish dine out on small crustaceans and fish, but they could easily find themselves on the menu of larger, predators. Yet when a team in the 1960s, led by the late, great ichthyologist John Randall, looked at the dietary habits of West Indian reef fish, no soapfish were found in the stomachs of the fish sampled, despite their apparent suitability and relative abundance.
So, they began to dig a bit deeper. Randall already had experience with the noxious excretions from these fish. Having speared a greater soapfish, Rypticus saponaceus, in the Florida Keys a few years earlier. Lacking the capacity to store it anywhere, he stuffed it inside his trunks. It didn’t take long for him to find out the hard way that the secretions from this individual were a ‘powerful urethral irritant’.
As well as being a skin irritant, the material is described as having a distinctly bitter taste when tested, so the function of the secretion was clearly a defensive one, and an effective one at that based on the dietary study. In fact, further laboratory investigations into the primary component within the mucus—grammistin—revealed just how unpleasant it can be.
Confirmation of the foul taste was observed during a predation event, whereby a lionfish, Pterois volitans, attempted to consume a small golden-striped soapfish, Grammistes sexlineatus, before immediately ejecting it, making further expelling movements with its mouth and consequently avoiding it for the rest of the duration within its captive confines. When a concentrated toxin solution was injected intraperitoneally into mice
