They may be extremely cute looking but pufferfish are the second most poisonous vertebrate in the world, after the golden poison frog. Certain internal organs, such as liver and eyes, and sometimes the skin, contain tetrodotoxin, a substance that makes them foul tasting and often lethal to fish.
To humans, tetrodotoxin is deadly, up to 1,200 times more poisonous than cyanide. There is enough toxin in one pufferfish to kill 30 adult humans, and there is no known antidote.
Amazingly, the meat of some pufferfish is considered a delicacy in Japan and is called fugu. It is extremely expensive and only prepared by trained, licensed chefs who know that one bad cut means almost certain death for a customer. Despite this, many such deaths occur annually! Have a look at the video below about how carefully it is prepared and how its eaten.
Pufferfish are poor swimmers and are very vulnerable to predators. Instead of trying to escape, pufferfish will ingest huge amounts of water (and even air when necessary) into their highly elastic stomachs, quickly turning themselves into a virtually inedible ball several times their normal size!
All puffers have pointed spines, so even if they are not visible when the puffer is not inflated a hungry predator may suddenly find itself with a mouth full of a pointy ball rather than a slow, tasty fish. The video below shows how the natural defense works when a puffer is caught by a moray eel.
There are more than 120 species of pufferfish worldwide. Most are found in tropical and subtropical ocean waters. They have long, tapered bodies with bulbous heads. Some wear wild markings and colors to advertise their toxicity, while others have more muted or cryptic coloring to blend in with their environment.
They range in size from the 1-inch-long (2.5-centimeter-long) dwarf or pygmy puffer to the freshwater giant puffer, which can grow to more than 2 feet (61 centimeters) in length. They are scaleless fish and usually have rough to spiky skin. All have four teeth that are fused together into a beak-like form.
The diet of the pufferfish includes mostly invertebrates and algae. Large specimens will even crack open and eat clams, mussels, and shellfish with their hard beaks. Poisonous puffers are believed to synthesize their deadly toxin from the bacteria in the animals they eat.
Some species of pufferfish are considered vulnerable due to pollution, habitat loss, and overfishing, but most populations are considered stable.