There are just under two hundred species of animals known as pufferfish. Nearly all are marine and most are found in tropical seas. In New England we have only one species, the Northern Pufferfish (Sphoeroides maculatus), although at least two southern Atlantic species can be found as strays.
Puffers are fierce predators, but are known more for their protective behaviors, the most impressive of which is their ability to inflate themselves with air or water, increasing their size dramatically. Unlike many land predators, fish generally swallow their food whole. If it can't fit down its throat the potential prey is passed up (there are, or course, many, many exceptions to this rule).
One common myth concerning this defense is that a puffer will inflate itself when it senses danger. Although it is able to inflate very quickly, this is largely a last line of defense, used only when it is actually grabbed by a predator. Since the fish is unable to swim well in this condition (speed is its first reaction to a predator) it is mostly helpless when enlarged. Once the puffer is released it immediately deflates and swims away.
The mechanism used to fill the body with water is ingenious, and involves a unique flap-like structure which lies flat against the bottom of the mouth. When a mouthful of water is taken in this oral valve slides up against the mouth opening preventing the water from escaping. The flexing action of the large muscle that controls this valve simultaneously propels the water forcefully down the fish's throat and into the stomach. With each gulp of water the puffer increases in size. When the water needs to be released the oral muscle relaxes and the pressure of the stretched skin and stomach shoots the water back out the mouth (exactly like how the pressure of a filled balloon shoots the air out when the pinched opening is released). As a side note, since the water is stored in the stomach you don't want to demonstrate your pufferfish's talent right after it has eaten. The entire stomach contents of the fish is regurgitated along with the water and it's not a pretty sight.
Although I haven't been able to find any documentation of this, I've discovered that these fish practice puffing themselves up each morning. I assume this exercise keeps the skin flexible for when this defense is needed for real. I'm also assuming that, for the reason stated in the paragraph above, this is done only in the early morning because puffers are diurnal and will not have any food left in the stomach at this time.
The skin and organs of the puffer contains a powerful biotoxin known as tetrodotoxin. Nevertheless, these fish, known as fugu in Japan, are edible if prepared properly. Toxicity varies among species and although the Northern Puffer is much less poisonous than other species (there are no known fatalities from eating S. maculatus) some Pacific puffers are deadly if even the slightest amount of toxin is consumed. (Tetrodotoxin is one hundred times more deadly than cyanide.)
Tetrodotoxin is a neurotoxin that acts by paralyzing the diaphram and victims that eat a tainted dish can take up to full day to succumb to the poison. Needless to say, it's not a pleasant way to go. 50% of fugu poisoning cases in Japan are fatal and there is no antidote. You either die or you don't and there's nothing a doctor can do about it. The good news is if you survive the first 24 hours you'll probably live.
Fugu chefs in Japan are trained and licensed to prepare this delicacy for adventurous diners and the training process for these chefs may be as long as ten years. Fugu is often served in thin raw slices presented in the pattern of the chrysanthemum, known in Japan as the "flower of death". Nice touch.
Restaurants in the U.S. that serve fugu are usually required to import detoxified and frozen puffer flesh from Japan. If you would like to try this dish expect to shell out about $200 per plate. And from what I understand, the best chefs are able to cut the fillets so that a tiny amount of toxin remains, leaving the diner with a sensation of having consumed a mild narcotic (which, of course, is supposed to keep them coming back for more.)
You've heard of voodoo doctors (know as "bokors") in Haiti? Tetrodotoxin refined from pufferfish (or poison arrow frogs, which have the same compound in their skin) are used to create the infamous zombie effect.
As mentioned above, the Northern Puffer is our only native species, but there is a species called the Bandtail Puffer (below) that regularly strays from the south. Like most tropical strays, the bandtail does not survive our winters. This species is much sleeker and can move incredibly fast in short bursts.
As you can see, puffers have only one dorsal fin and it is set far back on the body. Immediately below this is the ventral fin. These two fins are used together to move the fish in a very unusual way by alternately waving back and forth. This method of locomotion is known as sculling and is found in few other families of fishes. The tail is reserved for quick bursts of speed when needed. You may also notice that this fish lacks the paired pelvic fins, normally found on a fish's belly. These fins, and their associated skeletal structure would interfere with the animal's ability to inflate if they were present. For this same reason, pufferfish are also nearly unique among fish in that they do not have ribs.
Puffers make up a family of fish known as Tetraodontidae, named for the four plate-like teeth found in the mouths of all species. The fused teeth form a powerful beak that is used to crush the hard shells of mollusks and crustaceans. The jaws are powerful and to watch a puffer take apart a crab or lobster is something to behold. The exoskeleton is ground up, the flesh swallowed and the crushed shells spit back out.
Because the northern puffer feeds mainly on crabs the teeth become eroded over time. Like hamsters, the teeth constantly grow to replace the parts that are steadily worn away. This is a vital bit of knowledge if this fish is to be kept in captivity. If fed soft foods like clam meat or squid the teeth will grow until it can no longer close its mouth. If this happens the fish will slowly starve, and it appears this is what happened to the poor guy in the photo below which appears on an aquarist site I happened upon.
You can see the fish is emaciated by the relative size of the eyes and head compared to the wasted away body. Compare this to the healthy fish below. Notice on this fish the eyes are positioned on top of the head. This allows the fish to bury itself under the sand (yet another protective behavior of this animal) and still be able to see both threats and prospective prey while hidden.
Finally, what would a Marine Life Series diary be without a personal anecdote? For years I would catch these fish as young inch-long specimens. But after a few years every one would develop a bulge under its jaw, stop eating and die. Everyone I spoke to who tried to keep these fish in captivity seemed to have the same story. I finally relented and decided to simply keep them for only a year or two and then release them. Turns out Northern Puffers use up iodine faster than most types of fish and develop goiters which eventually grow to the point that the animal can no longer swallow food. Simply adding tiny bits of liquid potassium-iodide solution to the aquarium each week solves this problem.
Fun Fact: Captain James Cook is credited with recording the first (Western) case of tetrodotoxin poisoning during one of his voyages. Many of his crew reported feeling ill and numb after eating this strange inflatable fish and the whole catch was thrown to their on-board pigs, all of which were found dead the next morning.
Other diaries in this series can be found here.
[This essay was originally published to Daily Kos on October 13, 2006. Next week’s entry will be an original diary called "Understanding Krill".]