108 Sharks: The Animal Answer Guide
Do sharks have parasites?
We like to think of big sharks as residing at the top of the food pyramid,
surpassed only by an occasional killer or sperm whale. But in reality, each
shark is a tasty, swimming platform for a zooful of smaller parasitic animals
that feast on its blood and body tissues. Shark parasitology is a popular field
of study because of the intimate evolved responses between a vast diversity
of parasites and their shark hosts. Some parasites live in or on only one type
of shark and attach only in a particular place inside or outside the shark,
and only during a particular part of their life cycle. (Earlier life stages first
parasitize invertebrates, and then the small fishes that eat the invertebrates,
linking parasite life cycles to the entire food web.) About 1,500 different
parasites are known from sharks, skates, and rays, with each elasmobranch
species host to between 3 and 14 unique species; no doubt, many more will
be discovered.
Remarkably, according to shark parasitologists Janine Caira and Claire
Healy, “no organ system of elasmobranchs has escaped the attention of one
or more groups of parasites.” If we performed a CT scan across a shark,
from head to tail and including internal organs, we would find parasites in
the following shark organs:
■ Skin—One type of copepod crustacean (a relative of shrimp and crabs)
lives only on the pelvic fins of Blue Sharks, and one monogenean flat-
worm lives only on the undersides of certain skates. Other skin parasites
include a snail that lives on the dorsal side of torpedo rays, 20 species
of leeches, 275 species of copepods, 200 other monogenean flatworms
(8 of which occur on chimaeras), three types of nematode roundworms,
barnacles that attach to fin spines and flesh, amphipods (another shrimp-
like crustacean), branchiuran fish lice, isopods (same group as pill bugs),
and a few cestode tapeworms and digenean flukes.
■ Eyeballs—Eyeball parasites include several copepods (see below re-
garding Ommatokoita on Greenland Sharks), a leech on Spiny Dogfish,
and a fluke on Whitetip Sharks.
■ Olfactory bulbs (the complex foldings inside the nose that lead via the
olfactory nerve to the brain)—Among nasal parasites are ostracod seed
shrimps, isopods, copepods, roundworms, leeches, and flatworms. One
copepod infects the Barbeled Houndshark (Leptocharias smithii), the
head of the parasite being lodged in the olfactory lobe of the brain and
the tail resting in the olfactory bulbs. A roundworm has also been found
wrapped around the optic nerves and much of the brain of a Spotted
Eagle Ray.
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