Quick: what’s the most poisonous fish in the sea?  “Stonefish!” you venture, you Clever Observer, you!  For why else would there be an accompanying picture of a stonefish to the question?  I applaud your astuteness; perhaps you have a hidden propensity for piscine classificationism.  And yes, confirmed, the stonefish is indeed the most poisonous fish in the sea, unless you are a marine specialist, and know of some runners-up which on some lists surpass the stonefish for venomousness, but for our purposes, we shall grant you the correct answer of genus Synanceja, and you shall crow with rare eruditious pride.

The stonefish is a sluggish thing, and left to its own hum-hummery, will simply sit or drift near the bottom of the shallow waters of the Indo-Pacific; it is hardly an aggressive leviathan.  You needs must step upon it, or squeeze it, to activate its venom, and even then, a light squeeze usually results in only a smallish squirt; it’s only when you really put pressure on the poor thing that it becomes lethal — rather metaphoric, that. 

An interesting fact about the stonefish:  it is quite edible in, say, the form of sashimi, for the chef simply excludes the venomous quilly-bits, leaving the tasty rest.  A second even more interesting sidenote:  the stonefish can survive for nearly 24 hours out of the water, so, you must watch for it along the shore lest it sting you.

Hint:  it looks like a stone.  I don’t suppose that helps much, does it?  Well, if you step on a stone such as resembles this picture, and it injects you with a lethal toxin, yes, perhaps you may perish, but at least you will have the satisfaction of having properly identified a member of the Synancejidae family, which ought add to the value of your final moments, at least according to the classificationists who, in some capacities at least, have the final word.