A very potent toxin infrequently present in planktivorous species of fish, such as sardines and sardinellas, in tropical waters. The toxin has also been reported in species of horse mackerel, (Decapterus marosoma) and trigger fish (Melichthys vidua), and crabs. The toxin, a neurotoxin, is derived from the feed of the fish and causes symptoms similar to those of ciguatera, but with a higher mortality rate, around 50% of cases. The causative chemical has been identified as palytoxin, a toxin found in various species of arine algae. These marine algae are assumed to be the source of the toxin present in fish.