6 Pufferfish blink by sucking their eyes into their sockets. 

The wide-set, bulging eyes of the pufferfish are one of their distinctive features. They are unique because the puffers can retract them up to 70% into their head while the skin around them contracts towards the center. Apart from sharks, no other fish species have eyelids and do not require blinking since the water clears their eyes. 

That is not the only thing they can do with their eyes. The puffers can move their eyes independently of each other, allowing them to scan a wide range of space around them. They can also direct both their eyes forward to gain amazing depth perception. They also have extremely good vision helping them spot even small prey. 

Some species of puffers have special layers of iridescence that reflect sunlight from above, just like a polaroid lens or mirrored sunglasses. This essentially removes the glare underwater, and the remaining light that gets filtered through improves their visual range immensely. (1, 2, 3)

7 An adult pufferfish contains enough tetrodotoxin to kill 30 adults. 

Usually found in the liver, skin, eyes, and sex organs of the pufferfish, tetrodotoxin (TTX) is an extremely potent neurotoxin. Certain types of symbiotic bacteria produce the toxin and are also found in triggerfish, porcupinefish, and ocean sunfish. Historically, pufferfish eggs were used by the Chinese sometime between the 21st and 2nd centuries BCE at milder doses to treat seizures. 

In mice, as little as 334 micrograms of TTX per kilogram of body weight is lethal, and intravenously, just eight micrograms are enough to cause death. In comparison, you need 8,500 micrograms per kilogram of potassium cyanide to have a lethal effect. Tetrodotoxin is 1,200 times more poisonous than cyanide. 

Once ingested, symptoms usually develop within 30 minutes to a few hours. But a lethal dose can present symptoms within 17 minutes. The symptoms include tingling or numbness of lips and tongue, hypersalivation, headache, weakness, sweating, lethargy, losing coordination, shaking, inability to speak, paralysis, and cyanosis. 

Depending on the dosage, the patient could recover, enter a coma, or die in four to six hours. If 24 hours pass without death, the patient often recovers from the symptoms in a few days. Treatment usually includes emptying the stomach, using activated charcoal to absorb the toxin, and other life-support procedures. (1, 2)

8 The white-spotted pufferfish makes elaborate circular sand formations to allure females during its distinct mating ritual.

The white-spotted pufferfish is a relatively small puffer species reaching just up to ten centimeters in length. The males of this species are known for creating nesting sites that are patterns of geometric circles and lines to attract females. Though these circles were first noticed by divers in 1995, it wasn’t until 2013 that the artist behind them was discovered in the waters of the Ryukyu Islands in Japan. Generally found at depths of ten to 30 meters, these circles are around two meters in diameter and take seven to nine days to create. 

They start by creating a simple circle first using their belly. Then they create intricate, almost maze-like patterns of peaks and valleys by moving their fins and pushing finer sand particles towards the center. The females can tell how large the male is by looking at the pattern and then making their choice. The males maintain the structure until spawning. After that, the female leaves, and the male stays to look after the eggs until they hatch. (source)

9 Fugu, a pufferfish delicacy, is potentially fatal if incorrectly prepared. Chefs must complete a two-year legal training to serve it.

Known as “fugu” in Japanese, the pufferfish is prepared in many forms, including stews, grilled, or sashimi, by slicing the fish into extremely thin strips to be dipped in soy sauce and vinegar. It has been consumed for centuries in Japan and China. In Japan, it was banned twice between 1603 and 1868 and between 1867 and 1912. Since 1958, a mandatory license has been required for preparing the fish. 

The dish is considered a delicacy in Japan and Korea, especially so in winter when the fish is fatter and tastier. Over 90% of the pufferfish served by licensed chefs and restaurants are farm-raised, grown in ponds filled with hot spring water. These fish have a much less chance of consuming the toxin-producing bacteria. The fatalities are generally seen among those who prepare the fish at home after catching them in the wild. (1, 2)

10 Dolphins use the puffers to get intoxicated. 

Because of their deadly defense mechanisms, pufferfish have barely any natural predators. The only known animals that can eat them are sharks, especially tiger sharks, which are immune to their toxin, and sea snakes. Dolphins, on the other hand, are a whole different story. They have been observed to play with pufferfish, poking them deliberately to get the defenses up and enjoy the intoxication by chewing on the fish. Dolphin groups play catch with the poor inflated puffer or pass it around, taking turns as they chew and enter a trance-like state.