Extreme Catfish |
| Garold W. Sneegas &
Dean A. Hendrickson, Ph.D. |
elow the city of San Antonio Texas
lies a vast aquifer known as the Edwards (Balcones Fault
Zone) Aquifer. Two rare and unusual catfish reside in the
aquifer, Satan eurystomus, the widemouth blindcat
and Trogloglanis pattersoni, the toothless blindcat.
They are the only known troglobitic catfish in the United
States. The only specimens of both species ever collected
have come from deep (1,200' to 1,500') artesian wells within
the city of San Antonio itself and parts of southern Bexar
County.
The Balcones Fault Zone is a complex system of limestone
strata (Edwards Limestone Formation) that has been fractured
and eroded over time by geological forces. Water travels
not only through numerous cracks and fissures but also through
massive underground caverns, streams and rivers. The limestone
strata slopes towards the Gulf of Mexico. In northern Bexar
County the limestone formation is exposed on the surface.
In the southern part of the county the formation is 3,000
feet underground. San Antonio's water supply comes from
an area of the aquifer known as San Antonio Pool and is
considered the "Good Water" zone. South of the
Balcones Fault Zone lies the Gulf Coastal Plain which contains
anaerobic, saline and sulfurous groundwater known as the
"Bad Water" zone. Water from both zones meet and
mix in a line that roughly parallels Interstate Highway
35. Blindcats reside along this narrow mixing zone and may
be dependant on the unique environment created at the mixing
point of these two zones.
No one knows for certain how the blindcats colonized the
aquifer. One theory suggests that during the last ice age
surface ancestors of the widemouth and toothless blindcats,
invaded cavities to escape cold temperatures. Over time
they adapted to life deep underground; adaptations and identifying
characteristics include no eyes, no pigment and no swim
bladder. The swim bladder has been replaced with a mass
of adipose (fatty) tissue believed to be an adaptation to
the great hydrostatic pressure encountered at the depths
they inhabit. Other adaptations include more highly developed
sensory systems, lower metabolic rates, smaller body size
(2 to 4 inches) and longer life cycles.
The widemouth blindcat is the top predator of the aquifer
and is believed to have a common ancestor with Pylodictis
olivaris, the flathead catfish. It has a similar
head shape, strong jaws and well developed teeth. The lateral
line is well developed and there are also numerous well
developed lateral line pores covering the head. The barbels
are also large and well developed. The widemouth blindcat
probably relies heavily on it's well developed barbels and
lateral line system to obtain food. Stomach contents examined
from the few specimens available, contained decapods, amphipods
and isopods. It is also believed that the widemouth blindcat
probably preys on the toothless blindcat.
The toothless blindcat is the most specialized catfish known.
It's closest surface relative is Ictalurus
melas, the black bullhead. It has evolved a unique
suckermouth with papery thin jaws and no teeth. The upper
lip has modified parallel folds of soft ridges. The lower
lip is small and turned into the mouth. No other catfish
has this type of mouth. The lateral line system is not as
well developed as the widemouth blindcat's system. The olfactory
senses of the toothless blindcat however are more developed.
Nostrils in the toothless blindcat are larger and the anterior
nostrils have a specialized flap that enhances water flow.
Black bullheads have taste buds, cells with cilia (short
hair-like extensions) covering their external skin. Microscopic
examination of the toothless blindcat's skin revealed a
densely packed covering of taste bud cells. The external
skin of the widemouth blindcat lacks these cells. The toothless
blindcat probably feeds on dead or dying invertebrates and
a fungus commonly found in the Edwards Aquifer.
The extreme inaccessibility to the blindcats habitat in
addition to water quality monitoring by state and federal
agencies, has protected the habitat of these two unique
species. The biggest threat to the blindcats is probably
over-pumping the aquifer beyond its' recharge capability.
Drawing down the aquifer could cause the sulfurous "Bad
Water" zone to encroach into and replace the "Good
Water" zone.
Prior to 1978 the scientific community had only three specimens
each of these two species. In 1977-78 a survey of the Bexar
County groundwater fauna was conducted by Glenn Longley
and Henry Karnei. Since their survey little work has been
done on either species. Access to many of the known sampling
sites has been limited by low flow rates of artisan wells
and denied access to previous collecting sites by current
land owners. Hopefully, at some point in the near future,
scientists will again be able to study these "extreme"
catfish
Photo's by Garold W.Sneegas
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