- Pfiesteria pisicida Has Multiple
Some Of Them Deadly.
- For millions of years, Pfiesteria piscicida
lived in obscurity on the bottom of rivers and estuaries. No one noticed
the microscopic organism and no one cared. All that changed when fish began
dying in Maryland and North Carolina. Pfiesteria piscicida can assume
24 different forms, including this fish-killing ameboid stage (North Carolina
- Today, the once-obscure single-celled
aquatic organism is the topic of congressional hearings, the subject of
books and newspaper articles, and the cause of a major decline in the lucrative
fishing industries of those two states.
- In the past six years, Pfiesteria has
killed more than 1 billion fish. But the organism whose name means "fish-killer"
in Latin is also dangerous to humans. Scientists and fishermen have developed
sores, headaches and other neurological problems from exposure to it.
- Scientists are just beginning to understand
what makes Pfiesteria so dangerous, and the initial insights are quite
- Loves Fresh Fish
- Pfiesteria is a dinoflagellate, a group
of largely saltwater microorganisms, some of whose members are responsible
for Red Tide, the phenomenon that makes shellfish dangerous for humans
- Some dinoflagellates behave like plants,
getting their energy from photosynthesis. Others, like Pfiesteria, behave
like animals, drawing nourishment from fish and microscopic plants and
bacteria. In fact, fresh fish appears to be the food of choice when Pfiesteria
is in its killer mode. It is the only dinoflagellate that causes massive
fish-kills and then disappears within 24 hours. Scientists have found
Pfiesteria in rivers and estuaries all along the southeast coast. But the
fish-kills have only occurred in Maryland and North Carolina.
- The organism has what amounts to multiple
personalities, taking on at least 24 different forms as it hunts, feeds,
swims and lies dormant. In just a few hours, Pfiesteria can go from rock-hard
cyst to fast-swimming hunter to gluttonous amoeba devouring anything in
- This shape-shifting ability has made
Pfiesteria hard to figure out. JoAnn Burkholder, the foremost expert on
the organism, first discovered it about nine years ago while analyzing
a fish-kill in North Carolina. Her research team at North Carolina State
University in Raleigh has studied it ever since. Their work has provided
much of the information and insight into the organism.
- From Non-Toxic To Toxic
- One of Pfiesteria's harmless forms is
as a dormant cyst, minding its own business at the bottom of warm, slow-moving
bodies of brackish water (mixtures of fresh and salt). But when the cyst
detects the presence of fish nearby, either through the oils or feces they
release, it kicks into action.
- Pfiesteria transforms itself, leaving
its hard shell and swimming up to the fish. Once nearby, it shoots out
a powerful toxin that seems to have two effects. First, it makes the fish
groggy, so it can't swim away. Then the poison begins to dissolve the fish's
skin, creating sores and bleeding.
- Then, before dinner time, Pfiesteria
undergoes yet another change, this time into an amoebic, jellylike creature
that eats flesh and blood. It's a slow, painful death for the fish.
- After the meal, the Pfiesteria will revert
back to its hard cyst phase and sink back down into the mud. The entire
episode all happens in a matter of hours.
- Scientists don't understand completely
how the Pfiesteria toxins work, but they think there are two distinct types,
which Pfiesteria releases in a kind of deadly cocktail. One type is water-soluble
and creates the neurological problems for fish.
- The second type is fat-soluble, which
allows it to penetrate the skin and slowly dissolve the tissue. This second
toxin is what produces the characteristic skin ulcerations and sores. Pfiesteria,
in its ameboid phase, then slurps up the syrupy mix of flesh and blood.
- The Greatest Mystery
- Perhaps the greatest mystery of all is
what made this ancient cell turn into a mass fish murderer in the past
few years. Burkholder and other scientists theorize that environmental
changes are to blame. In particular, they say that run-off from nearby
farms, especially pig farms in North Carolina, have dumped high levels
of animal waste and fertilizer into rivers and lakes. These high levels
give rise to blooms of algae and bacteria, which in turn spur a population
explosion of Pfiesteria. In cyst form, Pfiesteria feeds on the algae and
- Burkholder and company will continue
to study Pfiesteria, characterizing its potent toxins and determining what
exactly causes its population to reach deadly levels. At congressional
hearings next week, scientists, federal officials and members of the fishing
industry will testify about the threat to humans, and about how to devise
better measures to insure public safety.
- Scientists are looking for the attention
from the media and the government to provide the boost - and the money
- needed to fully understand the tiny cell that presents big problems.
- When Pfiesteria sits on the river bottom
in its non-toxic cyst form, it eats bacteria and algae to survive. But
when the tiny creature detects the presence of fish nearby, the cyst turns
into a flagellate and swims toward its prey. Once there, it releases a
toxin that stuns the fish. Pfiesteria then changes form again, into an
amoeba. In this stage, it begins to eat the wounded fish.