was reported that temperatures above the
low 70s stunt their growth due to faster
maturation—they stop growing when they
mature, so fast-maturing fish are smaller.
KALLMAN, & MORIZOT 1990
The highland swordtail was named after
the slave mistress of Hernán Cortés. It hails
from elevations up to more than ¾ mile, so
keep it cool. In nature it can be collected
under floating plants in sandy-bottomed
It is a stunning fish once acclimated
and comfortable, but I have found it to
be delicate. Since the strain has been
domesticated more during the past decade,
it may be hardier.
Temperatures above the low 70s may stunt the growth of Xiphophorus cortezi.
(LECHNER & RADDA 1987)
The sheepshead or swordless swordtail
was named after one of its collectors and
generally enjoys rocky, well-oxygenated,
flowing waters. Unlike its cousin X. cortezi,
it does better in a tank of its own. X.
birchmanni was introduced to the hobby
and scientific community earlier than most
realize: Collected in the 1930s by Myron
Gordon, he thought this was the lost
Montezuma swordtail, and it was treated as
such for several decades. It was later called
X. cortezi, which also proved to be false.
The male’s large yellow fins and humped
back have made quite a splash at shows in
recent years. I now see body sizes exceeding 3
inches. Recent research by Drs. Heidi Fischer
and Gil Rosenthal discovered that this finnage
is not used to entice females (as with mollies)
but to ward off competing suitors. The females
actually prefer smaller dorsals!
With Dr. Bob Wong, they later discovered
that males will spray their urine in the
direction of females to entice mating and
to distinguish themselves from X. malinche
and X. cortezi, who inhabit different parts of
their range. Sadly, pollution in its biotope is
disrupting this chemical communication
system and creating hybrid fish in nature.
X. malinche comes from high elevations and therefore requires cool temperatures to do well
in the aquarium.
X. birchmanni prefers well-oxygenated, flowing waters like those found in its native habitat.
come from the use of heavily planted (top
to bottom) species tanks, gentle water
circulation with frequent water changes, and
the liberal use of live and frozen foods.
The pygmy swords are noted for having a
variety of naturally occurring size and color
morphs among males. Be careful of sneaky
smaller males who may mate with females,
siring most of the fry. The large males are
less shy and more interesting courtiers.
Brood sizes are small.
reach an inch and females that reach 1½
inches. The original 1939 collector reported
lovely gold-morph males, as well as more
common brown-striped, blue-sheened boys
and girls. Temperatures in the low 70s suit
The Pygmaeus Clade
The pygmy swordtails are beautiful
charges that are shy and delicate in the
home aquarium. Their natural habitat is
the small swift rivers that arise in front of
the Sierra Madre mountain range, where
they favor the shady banks and springs.
The best results when keeping them
HUBBS & GORDON 1943
This nearly swordless swordtail from
the Río Axtla has smallish males that
KALLMAN, & MORIZOT 1990
A challenging species that benefits from
a large tank with lots of hiding spaces,
the high-backed pygmy swordtail prefers
the deeper, faster waters of the Río Choy
drainage. I found this species to be a
stunning but scrappy charge. Even as fry
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