|Click image to enlarge
Anatomy of a Shark
The Greenland shark’s liver, accounting for around one-third of the fish’s body mass, is
a valuable organ not only to the sharks, who need it to survive freezing waters but also
to humans. Europeans hunted and killed nearly 30,000 Greenland sharks each year during
the early 20th century for the oil found in its liver, extracting up to 135 litres of oil
from the liver of one large Greenland shark. Later, Dr. Astrid Brohult, a Swedish physician
treating children for leukemia, discovered that Greenland sharks were a good source of
alkylglycerols, a compound that boosts the immune system. Today, the Greenland shark’s
liver is used widely in natural medicines for treating immuno-deficiencies and provides
a good source of Omega-3 fatty acids. However, there is one drawback to using shark liver
oil for human consumption: mercury. As a top predator, Greenland sharks accumulate the
metal at levels dangerous to both sharks and humans.
The ’dead stare’ of a shark’s eyes is one of the first features people visualize when they
think of the aquatic predator. For the Greenland shark, this couldn’t be truer. Although
the eyes of most of the northern sharks themselves are not dead, the corneas of the eyes
are covered in a foggy glaze — the result of scar tissue created from a six-centimetre-long,
pinkish-white invertebrate, known as a copepod (Ommatokoita elongate). This parasite
attaches itself to the cornea of the Greenland shark, feeding on surface-layer cells and,
in the process, severely damaging the top-layer of the shark’s eyes with its dangling body.
Sharks can have up to 1,000 teeth in their mouths. Since this aquatic predator replenishes
its teeth as they fall out, this means that in a lifetime, a shark can have up to 20,000
teeth! Although this cartilaginous fish’s teeth have evolved over time, there is wide variation
in their dentition, depending on the shark and its general food source. Teeth for mammal-eating
sharks are serrated, useful for ripping out chunks of flesh, whereas the dentition of crab
and invertebrate-eating sharks are short, which is good for grinding up shells. And then
there are sharks that have no teeth at all. Swimming forward with wide-open mouths, they
filter plankton (tiny shrimp-like marine animals), from the water flow using their gills.
Number and location of fins varies greatly from one species of shark to another. In general,
however, sharks have one to two dorsal fins, located at the top of the animal, and used to
stabilize the shark and keep it from rolling. It has two pectoral fins, extending downward
and out from the side of the shark, behind the head, used for steering and lift. Males use
claspers in their pelvic fin (sharks tend to have one or more) found on the base of the animal
for copulation. Where the need for speed is essential, sharks use the caudal fin for thrust.
An optional fin, depending on the shark species, is the anal fin, located between the pelvic
and caudal fins.
Sharks are made from cartilage, which is more malleable than bone. In fact, it is the basis
for its taxonomic classification: Chondrichthyes class (cartilaginous fishes). Shark cartilage
has been the subject of intensive clinic research due to its angiogenic inhibitors, compounds
that halt the creation of blood vessels, which could potentially stop the spread of cancer
from a single tumor. As a result, using shark cartilage as a complementary medicine has sky-rocketed,
even though there is no scientifical proof that shark cartilage itself inhibits cancerous
growths in humans. Further, since shark cartilage is taken orally as a powdery substance,
any angiogenic properties the substance may have enters the digestive system instead of the
blood stream, and are lost from the body.
Contributor: Sarah Everts