poisoning is caused by eating contaminated fish.
Its NASTY and can have residual neurological symptoms for a loooong time. The "signature" symptom is that the sensations of hot and cold reverse (yikes!)
Any predatory saltwater fish in tropical (80F+) water can have it, with the odds going up with the size of the fish, as it is bioaccumulative. It is not destroyed by cooking as its a toxin, not a biological thing (like a bacteria or virus), so there is no way to make a contaminated fish safe (other than not eating it!) There is a field test for the toxin but its relatively expensive "per-use", and thus is not often used.
This, by the way, is why people say not to eat barracuda, but reality is that any predatory - AJs, wahoo, grouper and snapper along with others - fish from warm enough water can be contaminated with it as well. It is NOT limited to reef fish; anything that EATS reef fish can be contaminated too!
Dolphin (Mahi), due to their extraordinary growth rate, are less likely to be dangerous (they get big fast enough that they usually don't accumulate enough of the toxin to be dangerous before someone catches and eats them.)