Originally published in Coastal Angler Boston: December 2011
On a late season tuna drift, I noticed a few decent marks
passing along the bottom and I decided to drop a jig and teaser down. It didn’t take long before we had
enough cod on ice for a few dinners.
I’ve filleted a lot of cod and I’ve seen worms in most of
them, but the fillets from this day were particularly loaded with the little
critters… As usual all the typical crews’ response starting getting voiced –
“that’s nasty” , or “eh, just some extra protein”, and “don’t worry, they can’t
survive human digestion”, and several “no way, I’m not eating that.” among
others. I used to be in the extra
protein camp. Having researched
it, not anymore:
What are they?
The Cod Worm, or more correctly the Seal Worm (Pseudoterranova
spp) is a parasitic nematode. It is a roundworm that is present in an
estimated 75-90% of all Atlantic Cod.
They can be brown, red, pink, yellow or white in color. They can be found in many species of
fish but are most commonly found in cod due to their living on the bottom in
close proximity to grey seals. As
usual, blame it on the seals.
The Seal Worm has a 4 stage larval process. The life cycle begins when the final
infected host (usually a grey seal) releases eggs of the worm in their feces
into sea water. The eggs
immediately hatch into a larval stage.
The larvae are consumed by small crustaceans, which then are preyed upon
by fish. The 3 stage
of larval development has a specially formed tooth that enables penetration of
the gut into the flesh of the infected fish. This is stage that you see in the fillets of the cod. Finally, the host fish is consumed by a
marine mammal (or human) where the larvae reside in the bowel where they seek a
member of the opposite sex for mating.
The life cycle is completed when the female lays eggs that exit the
host’s body through its feces.
Humans are an accidental host of Seal Worms. They easily survive your digestion
process and can even complete the 4 stage of development in our
bowel. They can survive in up to
80% brine solution and can easily survive a low temperature smoking process.
The Good News (Sort of)
Fortunately, most of us are not frequent consumers of raw
cod, nor should we be. The worms
can be killed by freezing at -10 degrees F or by cooking to 140 degrees (keep
in mind that household freezers are typically set to 0 and cod is opaque and
flaky at 130). The commercial
processors use a candling table which shines a light up through the flesh
making the larvae easier to see.
This can be done at home with a pane of glass positioned over a
fluorescent lamp. The larval worms
might be 1-3 cm long, but only 5mm when coiled in the fish’s flesh. Needlenose
or tweezers are all you need to remove them. Soaking the fillets in brine or lemon juice can make them
easier to remove.
Basically remove all that you can see and make sure you
thoroughly cook the fillets for the ones you couldn’t. Or, just do what restaurants do - bread
and deep fry them.
So let’s say you consume a quantity of infested flesh – what
happens next? Potentially
nothing. You may pass them before
they take up residence. You can
even become mildly infested and be completely asymptomatic. The 3 to 4
stage of development can take from 3 days to 3 weeks. In this time, you may have the abdominal pain / distress and
you may experience other weird symptoms like tingling in the throat or
arms. In very rare cases you can
become allergic to the slime that that worms produce from their skin. Unless you are regularly consuming
undercooked or raw infected fish, the entire adult lifecycle will complete its
course within a month.
Do keep in mind that parasites have not survived most of
eternity by making their hosts sick.
Their entire reproductive lifecycle depends on the hosts maintaining
overall and intestinal health.
This is also not a new concern, with reports and scientific studies on
these worms from the 1950’s, and comprehensive studies of health effects from
over 30 years ago. You can
continue to enjoy catching and eating cod. Seal digestive systems are often loaded with these worms
because they don’t fillet, inspect, freeze, and then cook their catch, but you