Anatomy and
Physiology
Members
of the Tetraodontidae family generally share the same shape and general
characteristics. Pufferfish generally exhibit a torpedo-shaped body
with a somewhat anteriorly placed dorsal fin containing 7-18 soft rays.
The anal fin is situated ventrally, in line with the dorsal fin and containing
approximately 7-18 soft rays. The caudal fin is either moderately forked
or rounded. Pectoral fins are found just behind the gills.
Teeth are fused in a powerful jaw with a median suture apparent at the
midline, appearing as 4 fused teeth (hence tetraodontidae, meaning four
teeth). This is of particular use in crushing the shells of mollusks
and crustaceans. The eyes of pufferfish are somewhat large for its
body, and are capable of moving independently. These fish have smooth
bellies, or in some cases, backward pointing spines ventrally.
Click the first picture to
download and view a short movie of this figure-eight puffer swimming in
its tank. Note the dorsal and anal fins as its primary source of
propulsion, along with its pectoral and caudal fins, which are primarily
used as rudder.
(movie
courtesy of Keith L. Jackson) Perhaps
the most distinctive visible characteristic is the fact that Tetraodontidae
can inflate their bodies with water when threatened. This is accomplished
by the use of an oral valve located on the floor of their mouth.
Let's let a real expert explain this amazing process. The following
excerpt is taken from "When Fish Bite", an article by Frank Stephenson
for "Research and Review".
"In studying
the feeding behavior of the Tetraodontiformes, the group of fishes to which
the puffer belongs, Dr. Peter Wainwright stumbled upon the secret to the
fish's bizarre attribute-a special oral valve attached to the floor of
its mouth. Scientists who had previously noted the organ's presence
had speculated that it played some part in inflation, but couldn't pin
down what that might be. Wainwright has been able to explain the organ's
vital role and also to show how the whole process works. After filling
its mouth with water, the fish flexes a large muscle at the base of the
oral valve which then catapults forward against the entire front of the
mouth, forming a tight seal against the back of the front teeth. This prevents
the water from escaping while a "plunger" type of apparatus -a mechanism
driven by a highly modified gill arch called a branchiostegal ray-mounted
at the base of the throat forces the water upward where it shoots down
the fish's esophagus and into its stomach. Using a series of electrodes
embedded in the puffer's head muscles, Wainwright learned precisely which
muscles are involved and how they fire in rapid sequence to accomplish
the task. The trick doesn't stop there, of course. Scientists have long
known that puffers have stomachs and skin of unparalleled elasticity. Unimpeded
by ribs (puffers don't have them), the fish's water- (or air-) filled stomachs
are thus free to balloon, making their owners a difficult mouthful indeed
for any passing predator."
These amazing
fish don't stop there, however. Most people have heard of "fugu",
which is actually a prepared Japanese dish using the Fugu Puffer as the
main constituent. Those of you who familiar with fugu have undoubtedly
heard of fugu poisoning. One of the most powerful poisons in the
world is present in many pufferfish. The poison is called "Tetrodotoxin".
This is such an interesting subject, it has been given its own page on
this site. Click the link below to continue to this subject.
