Porcupine Fish

Porcupinefish have the ability to inflate their body by swallowing water or air, thereby becoming rounder. This increase in size (almost double vertically) reduces the range of potential predators to those with much bigger mouths. A second defense mechanism is provided by the sharp spines, which radiate outwards when the fish is inflated. Some species are poisonous, having a tetrodotoxin in their internal organs, such as the ovaries and liver. This neurotoxin is at least 1200 times more potent than cyanide. Some scientists believe the poison is produced by several types of bacteria that are somehow obtained via the fish's diet, because fish bred in captivity are not poisonous, however, other scientists are skeptical of this theory. As a result of these three defences, porcupinefish have few predators, although adults are sometimes preyed upon by sharks and orcas. Juveniles are also preyed on by tuna and dolphins.