Issue 7, April 2002
Hagfish Aren't So Horrible After All
Integrative Biology, University of California at Berkeley
are among the many curious organisms living in the deep oceanic
benthos. At first glance, the hagfish's dark, quiet environment
appears extremely stable and unchanging - even quite dull. It's
not always so still, though. Scavenging brittle stars may stampede
over the soft silt mounds created by creatures that live within
the sediments, destroying the mound and possibly trapping the inhabitant
beneath the mix of silt and mud. "Benthic storms" of sudden
water flow can occur from either falling objects or large marine
fauna. Sinking human vessels or gigantic food falls such as whale
carcasses can cause large disturbances.
Looking closer, one might discover an alarming sight: Those dead
organisms resting on the deep sea floor are actually pulsating!
What could cause such movements? Usually, it's a passel of scavenging
hagfish feeding on the carcasses from the inside out.
The muddy bottom of the deep sea can seem quite creepy, and hagfish
only enhance this impression. In the deep sea's high-salinity and
high-pressure environment, there is little light, except that coming
from eerie bioluminescent creatures who make their livings in complete
darkness. Water flow over the soft silt is nearly nonexistent. The
pointy tracks of polychaete worms remain for long periods of time,
and even the indentations left by deep-sea submarines can be identified
months later. Hagfish favor the soft muck of these highly saline
waters, and tend to burrow in the mud or under rocks; they cannot
withstand bright light or warm water. In fact, hagfish are mostly
found near the mouths of rivers or at depths of 25 m or more, with
the deepest-dwelling species (Myxine circifrons) found at
more than 1000 m below the surface.
Primary productivity (plant growth) does not occur in the deep sea.
Rather, organisms subsist upon particulate organic matter, the "marine
snow" that slowly falls from the ocean's surface, or survive
as lowly deposit feeders, swallowing 99% inedible debris for every
1% of edible organic substance. The natural foods of hagfish include
worms and benthic infauna (creatures that live within seafloor sediments)
or epifauna (creatures that live upon the sea floor), but hagfish
are more infamous as voracious scavengers. Preferring the soft,
inner flesh of dead and decaying marine life, hagfish can actually
burrow into an organism's body and devour it from the inside out,
resulting in the pulsating appearance of the dead body.
"Hagfish should be called ‘fish' with the knowledge that they
are only distantly related to the world's fishes," says Dr. Steven
Webster, senior marine biologist at the Monterey Bay Aquarium in
California and 24-year veteran of invertebrate zoology. According
to Dr. Webster, hagfish are "an ancient group that branched off
from the chordate line probably before the vertebrate column appeared
in the tree of life." Webster appreciates hagfish for their evolutionary
and taxonomic heritages. As members of the class Agnatha and order
Cyclostomata, they are one of a handful of jawless fishes with odd
sucker-shaped mouths. Agnathids such as lampreys and hagfish appear
quite worm-like, but they are actually scaleless, chordate fish
(embryologically related to vertebrates and others in the phylum
Chordata). The hagfish at the Monterey Bay Aquarium reside in the
"Mysteries of the Deep" exhibit, where they lie happily
curled on the bottom next to a fake fish carcass.
Hagfish have yet another curious feature: They produce a viscous
white slime. While lampreys do not have slime glands, hagfish have
75 to 100 glands from head to cloaca, with ducts that release thick
globs of exudate when the hagfish is disturbed. Hagfish slime, being
thick and sticky, is known to be extremely unfriendly to the touch
and can appear shockingly suddenly. Moreover, seawater enhances
the viscosity and thickness of the slime. It is said that when you
have one bucket of angry hagfish, you will soon need another bucket
for the overflowing slime.
Hagfish produce slime via two pathways: holocrine (slime glands)
and merocrine (epidermal, through the skin). The scaleless hagfish
epidermis consists of three cell types, all tightly knitted together
with collagen fibers to form a flexible grayish "sheath":
small mucous cells, epidermal thread cells, and large mucous cells.
An extensive capillary network supports the dispersal of bio-products
quickly and effectively, with capillary loops forming ball-like
complexes around each slime gland.
occurs when the hagfish is alarmed or disturbed. Gland cells, which
include gland mucous cells (GMCs) and gland thread cells (GTCs),
rupture and release their contents to the outside seawater. GTCs
release intermediate filament (IF) biopolymer, resulting in IF polypeptide
sequences which are similar to skin keratins. GMCs expel mucins.
The IF threads and mucins interact with each other, and have a high
capacity for absorbing water. Following contact with seawater, the
aggregate forms thick cables, not unlike the pre-ovulatory cervical
mucous that protects the human uterus. Water is then expelled and
the formation of the slime mass is complete.
Other than for individual defense and for frightening humans, the
slime may be used to deter predators from hagfish nest eggs. Hagfish
also defend themselves by tying their bodies into knots, but this
may also help to wipe off any excess slime from their eyes and nostrils.
Sneezing also aids this process. If a pulsating mass in the benthos
sneezes, it is certain that hagfish are hiding inside!
Dr. Webster himself has experienced what he calls, "the gooiest,
gloppiest, most amazing slime," during his study of ichthyology
in the 1960s. Having completed research on these fascinating creatures
long ago, Webster remarked that they are very long-lived animals,
a fact discovered through research at the Monterey
Bay Aquarium Research Institute (MBARI). The specimens currently
residing at Monterey Bay Aquarium have not been replaced since they
were first obtained years ago.
Hagfish have also been known to attack and suck the flesh of hooked
or netted fish. This leaves a jagged hole in the hapless victim,
a horrid sight that might suggest to some that hagfish are ugly,
nasty animals. However, hagfish are also active predators in addition
to scavengers. Although not beautiful creatures, it's somehow reassuring
to know they are not only found within rotting carcasses.
Presently there is a significant interest in the use of hagfish
in scientific study and in the economy. Hagfish have proven useful
in the study of tumors. The cooperation of body parts in producing
slime (essentially polypeptides) is also important in examining
functionality, morphology, and metabolic actions.
A great commercial value is placed upon hagfish, especially in Korea,
where hagfish meat is eaten. Skins are fashioned into "eel"
leather items as well; however, due to their low fecundity and turnover
rate, hagfish may be in danger of depletion from over fishing. Some
possible future uses of hagfish slime include use as a replacement
for egg whites in cooking, and oils in various ointments. Imagine
frying up some bacon and slime for breakfast!
Hagfish do not have a cerebellum or eye muscles; however, to deem
these animals helpless and dumb based on poor visual ability is
wrong. As chemosensory and mechanosensory specialists, hagfish possess
extraordinary sensitivity and compound sensory organs. An elaborate
scheme of free nerve endings innervates their skin. The nervous
system contains axons of different diameters for varying nervous
signal speeds. Hagfish swim with ease and flexibility, using gliding,
"figure eight," and vermiform (worklike) motion. They
also possess a lateral line system and an advanced chemosensory
system with Schreiner organs, which resemble taste buds.
General human disgust with these creatures is apparent in the generally
low level of interest in hagfish. But perhaps one day, with more
research, hagfish will enable us to cure cancers of the skin. Or,
the slime may indeed end up as a favorite egg substitute. Then,
fisheries management will realize the importance of maintaining
their populations, and we will all have a bit more interest in the
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experimental use of hagfishes". The Biology of Myxine. Eds.
Brodal, Alf and Ragnar Fange. Oslo: Grondahl & Son, 1963.
Blackstad, T.W. "The skin and the slime glands". The Biology
of Myxine. Eds. Brodal, Alf and Ragnar Fange. Oslo: Grondahl & Son,
Braun, C. and R.G. Northcutt. "Cutaneous exteroreceptors and
their innervation in hagfishes". The Biology of Hagfishes Eds.
Jorgensen, Lomholt, Weber, Malte. London: Chapman & Hall, 1998.
Garrison, Tom. Oceanography. Third Edition. Belmont: Brooks-Cole
and Wadsworth, 1999.
Spitzer, R.H. and E.A. Koch. "Hagfish skin and slime glands".
The Biology of Hagfishes Eds. Jorgensen, Lomholt, Weber, Malte.
London: Chapman & Hall, 1998.
Von During, M. and K.H. Andres. "Skin sensory organs in the
Atlantic hagfish Myxine glutinosa". The Biology of Hagfishes.
Eds. Jorgensen, Lomholt, Weber, Malte. London: Chapman & Hall, 1998.
Welsh, U., S. Buchl, and R. Erlinger. "The Dermis". The
Biology of Hagfishes. Eds. Jorgensen, Lomholt, Weber, Malte. London:
Chapman & Hall, 1998.
Pers Comm. Steven K. Webster,
Ph.D. Senior Marine Biologist, Monterey Bay Aquarium 886 Cannery
Row Monterey, CA 93940
of Young Investigators. 2002. Volume Five.
Copyright © 2002 by Jean Lee and JYI. All rights reserved.