NANFA-L-- RE: Amazon Mollies

Doug Ebeling (
Tue, 8 Feb 2005 09:59:13 -0600


I have collected Sailfin Mollies from the San Marcos about 3 years ago.
Somewhere around here I have the Federal Recovery Plan for the Endangered
Species of the San Marcos (Fountain Darter, Salamander, San Marcos Gambusia,
& Wild Rice). I don't remember if it has references to the Molly release or
not. I've run out of time, but tonight I'll look for it and see.

You are correct about us swimming the San Marcos year round. This is our
canoeing season and the San Marcos is our usual trip. (Our canoeing
sometimes involves a bit of swimming.) Summer time we abandon the rivers to
the tubing civilians.

Best Regards,
Doug Ebeling
Spring, Texas
Cypress Creek, San Jacinto River

-----Original Message-----
Date: Mon, 07 Feb 2005 14:04:24 -0600
Subject: Re: RE: NANFA-L-- Amazon Mollies

Hi Jan,

I have read conflicting statements about when the Amazons were released into
the San Marcos (via a broken aquarium that drained out a floor drain and
into a storm outlet according to Clark Hubbs). Some accounts, albeit not
"official" ones, say 1939, others give 1954, and some simply say
mid-twentieth century. From the sources you cite below, the 1954 date seems
likely. Clark would be able to say definitively. I checked his checklist
in the Texas Journal of Science hoping it would have a reference, but there
is nothing there. I don't have Brown's (1953) report, but it should say if
the introduction was prior to 1953. Another possible source of the correct
date is a report by Courtenay and Meffe in Meffe and Snelson's (1989) book
on livebearer ecology and evolution. My copy disappeared with a student who
evidently needed it badly ;-) . I've checked about 40 references this
morning, and not found the date, just secondary and tertiary statements
about the fish being intr!

BTW, people tell me that Amazon's are difficult to find in the San Marcos R.
these days, and have been ever since the extreme floods of the late
nineties. If the floods are responsible, that would be one of the only
incidences known in which floods actually altered the fish fauna of a

I haven't seen Doug's report either, but most references (for example, Page
and Burr's Peterson guide) simply report the Amazon as being "probably
introduced" in the Nueces. The original reports from the thirties (by Carl
Hubbs and Robert Rush Miller) describing the fish and reporting on its
unisexuality make no mention of a population in the Nueces. Clark Hubb's
Texas checklist states unequivocably but without attribution that the
population in the Nueces was introduced. Whether Amazons occur in the tiny
handful of streams (Santa Gertrudis Creek, Petronila Creek, Los Olmos Creek)
tributary to Laguna Madre in the hundred miles between the Nueces and the
Arroyo Colorado I do not know. I know I have never taken them from those
streams, but my sampling has been very limited. Amazon mollies reportedly
occur in ditches and ponds on N. Padre and Mustang Islands today. If they
are absent from those streams, that would suggest on zoogeographic grounds
that the Nueces population !
is introd

Brown's association of molly numbers with winter water temperatures in the
streams mentioned is interesting. Sailfin mollies and formerly Amazon
mollies were super abundant in the San Marcos in the 1990s, and the San
Marcos, like the Comal but unlike the Guadelupe or the _MODERN_ (20th
century) San Antonio is essentially a giant spring run with very nearly year
round constant temperature. At San Marcos, Texas people swim in the San
Marcos essentially year round -- Texans, not just Canadians on vacation. I
don't know the temperature limits for mollies, but in the RGV, when cold
fronts would kill blue tilapia by the thousands in ditches, I never found a
dead molly. I do understand that critical temps do not necessarily indicate
the minimum temps that can be inhabited, but it seems hard to me to
reconcile what I know about mollies and what I know about the San Marcos
with a temperature limitation for them.
Thanks for bringing these points up.
David L. McNeely, Ph.D., Professor of Biology

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