VIETNAMESE BAIT WORMS: GREAT BAIT OR INVASIVE INTRODUCTION?

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VIETNAMESE BAIT WORMS GREAT BAIT OR INVASIVE
INTRODUCTION? Doug Miller1, Pamela Davey
Huggins2, Christine Muir1, Abigail Bradley1, Jill
Brown1 and Ryan Dale1 1Graduate College of Marine
Studies, University of Delaware, Lewes, DE, USA
2Fairmont State College, Fairmont, WV, USA
The biggest, baddest, pinkest polychaete of them
all.
What are these worms? Sold as nuclear worms or
nukes, Vietnamese bait worms are polychaetes
(segmented marine worms) which belong to the
genus Namalycastis and the family Nereididae.
They are related to the common clam worm of the
east coast of the US, except theyre much bigger.
Where they live and what they eat Vietnamese bait
worms do quite well in our lab under conditions
which simulate local salt marshes. In culture,
they inhabit shallow burrows in mud underneath
decaying vegetation. They appear to be tolerant
of hypoxic conditions, although like all marine
invertebrates, they respire aerobically and are
poisoned by high levels of H2S. Fecal pellet
analyses suggest that nuclear worms are
nonselective deposit feeders and will ingest
anything they can fit into their mouths,
including sediment, seaweed and cellulose fiber.
How big are they? Large specimens can reach
lengths of 300 cm (9 feet) in the wild. Cultured
specimens at the College of Marine Studies are a
more modest 100-200 cm (3-6 feet) in length.
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Temperature limits Nuclear worms like it hot.
They thrive at 30-35 C (88-96 F) and 90-100
relative humidityin a word, tropical conditions.
Interestingly, however, nuclear worms can
survive to near 12 C (mid-low 50s F) if they
are slowly acclimated to dropping temperatures.
Where are they from? Most members of the genus
Namalycastis inhabit low salinity areas in
tropical and subtropical regions of the world.
Nuclear worms are shipped to the U.S. from the
Mekong Delta in Vietnam.
Why are they imported from Vietnam? Nuclear
worms were first introduced to the Mid Atlantic
region in the mid 1990s for use as bait. Each
worm can be cut into over 40 pieces, making them
relatively cost effective. Also, unlike other
worms, nuclear worms neither bleed when cut nor
bite when annoyed. Why are scientists studying
Vietnamese bait worms? They are a previously
undescribed species of polychaete. If they were
accidentally released into the environment, they
might become an invasive species. Or notwe just
dont know right now.
Salinity tolerance Nuclear worms are remarkably
tolerant of a wide range of salinities, from
nearly fresh water to full-strength seawater.
They are termed euryhaline and adapt to
changing salinity by absorbing or releasing water
from their body fluids.
Great bait or introduction of an invasive
species? Judging by their sales at local bait
shops, nukes are a popular bait. Because they
require tropical temperatures, it is generally
thought unlikely that this species could over
winter in the Mid Atlantic region and become
established, and there is no indication that they
would become a pest species. To provide
scientific support for these assertions, we are
continuing laboratory experiments to delimit
which areas of the Southeast US coast are
susceptible. Next summer, we plan additional
experiments to study their survival when cut for
bait, their ability to regenerate, their live
prey diet and any potential impact on other local
fauna.
During the summer of 2002, nuclear worms
received a lot of media attention because their
packing material contained potentially harmful
bacteria. However, scientists still had very
little information about the worms themselves.
Therefore, we decided to study some of their
basic natural history.
Research supported by the Aquatic Nuisance
Species Research and Outreach program of the
National Sea Grant Office.