b. Inspector Action. You should detect organism(s) present in the product and
determine whether or not parasites are present.
c. Detection Methods. Candling the fish by incandescent lights is often used to
detect parasites in fish. The parasites show up as dark areas or spots, not to be
confused with blood spots or bruises. Other methods to detect parasites include
ultraviolet (UV) light, high salt concentrations, and freezing out. The latter two methods
force the parasites to the surface of the fish.
d. Disease-Causing Parasites of Fish.
(1) European or broad tapeworm. The fish tapeworm, called broad or
European tapeworm (Diphyllobothrium latum) is identified by its segmented body and
broad head. The tapeworm is found in cyst form in fish flesh. It is mostly found in the
US in pike and pickerel fish midwestern or Canadian lakes. It is also found in some
European freshwater fish. In man, it may grow to its adult size of 20 to 30 feet (within
the intestinal tract). Infection (called diphyllobothriasis) is the result of eating raw or
inadequately cooked fish. Proper preparation will render the cyst harmless. If it is
cooked 10 minutes at 122F (50C) or frozen at 14F (-10C) for 24 hours, the parasite
will be destroyed.
(2) Roundworm larvae. The roundworm larvae of the Anisakidae family are
found in squid and saltwater fish from many parts of the world. Infected fish are
common in US markets and may cause acute gastrointestinal distress (anisakiasis).
This is caused by the ingestion of larval nematodes of the Anisakidae in raw or
improperly prepared (salted, freezing, cooking, smoking) saltwater fish and squid.
Heating at 140F (normal cooking temperature) or freezing at 4F for more than 60
hours kills the larvae.
e. Commercially-Important Parasites of Fish.
(1) Copepod (sea lice). The copepod (Sphyrion lumpi) is a small
crustacean commonly found in Atlantic Ocean perch (Sebastes marinus). Like other
crustaceans, it has a claw-like appendage which attaches to the flesh, causing areas of
inflammation and abscesses. As a result, these parasites are usually visible to the
naked eye. Trimming of the affected area is necessary to improve appearance;
however, the flesh may be consumed without harm.
(2) Flatworm. The flatworm (Prosorphynchus, a trematode of the
Bucephalus genus) is common to Pacific Ocean perch (Sebastodes alutus). This
parasite passes from fish to shellfish and back to the fish to complete its life cycle. It
encysts in the flesh, causing yellowish brown to black spots 1/8 inch to 1/4 inch in
length. They are not normally visible to the naked eye. These flatworms are harmless
to humans, but are removed for commercial purposes.