Blue Ringed Octopus


The blue ringed octopus is a relatively small sized brown octopus that develops vivid blue rings when it is threatened.  It is mostly found in the coastal waters off Australia such as the Great Barrier Reef.  Like the sea snake this genus is relatively inconspicuous until it is disturbed, when it can inject one of the most lethal venoms into its victim.  Most of the recorded bites are the result of tourists picking up the octopus from tidal rock pools or from accidentally treading on them.  A very dangerous action considering one average sized octopus (approx 26g) has enough venom to paralyse up to 10 humans.



The main constituent of the venom from the blue ringed octopus is tetrodotoxin, as shown below.  The toxin, which is also found in the puffer fish, is secreted in the saliva of the octopus.  Excellent info on TTX.




The toxin, unlike concentrated anesthetics, acts exclusively from the outside of the membrane.  As is clearly visible from the structure it is a relatively complex molecule that bears a positively charged guanadinium moiety.  It is the guanadinium ion that is of importance as it is able to permeate voltage-sensitive Na+ ion channels.  This part of the tetrodotoxin molecule lodges itself in the channel, while the rest of the molecule blocks its outer mouth.  Its association and dissociation is dependent on whether the gate is open or closed.  Some voltage-gated Na+ channels are actually insensitive to tetrodotoxin, most notable are those of cardiac muscle and nociceptive peripheral sensory neurons.



The most frightening fact concerning tetrodotoxin is that only a milligram or less, the amount that can fit on a pin head, is required to kill an adult.  The extraordinary lethality is attributed to its unusual structure coupled with the fact that it binds specifically to six separate sites on sodium ion channels.  As yet there is no known antidote to the toxin and treatment mainly consists of life-supportive measures, this can include artificial respiration along with gastric lavage using activated charcoal.


Puffer Fish


This crazy looking fish is a puffer.  It belongs to the order Tetraodontiformes which illustrates the origin of the name of the toxin it uses to stun and digest prey, tetrodotoxin.  However, the toxin is not actually produced by the fish, instead it is incorporated through the food chain in some of the bacteria it eats.  So, although puffers contain the same toxin as the blue ringed octopus they certainly acquire it in a different way.



The puffer fish is some what of a Japanese delicacy going under the name of Fugu.  The fish can only be prepared by a qualified master chef, but even then it is hard to eliminate the chance of poisoning as cooking cannot remove the toxin. This illustrates the method whereby humans become intoxicated, a completely insane option at the dinner table.  However, a friend insures me that the risk was well worth taking.  Those puffers taste good!  I'm not quite sure he was aware of the facts though and maybe, if given another chance, would actually turn it down.  Here's a few reasons why:


More than 100 people die each year from eating Fugu.


80% of ingested victims die.


Of all marine creatures puffers are amongst the most poisonous.


The toxin seems most concentrated in the ovaries and liver, with lesser amounts found in the intestines, skin and minute quantities in the muscles and blood.  Tell me, what part of the fish is not infected?


Again, there is no anti-venom to Fugu(tetrodotoxin) poisoning.


Anyone still up for eating a puffer?