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When
chairman of the American Livebearer
Association, it was pointed out to me that most hobbyists
began keeping fish by raising
guppies, platies, mollies and
swordtails. Unfortunately, with all but the
guppies, the other livebearers were created by crossing
various species with one another to create
colors and finnage generally not found in nature. The
guppies, meanwhile, have been bred to look
nothing like their native ancestors. The bright red, orange,
yellow and green swordtails often seen in
pet shops began as crosses between the X. helleri (one
of the larger and more attractively colored
wild swordtails) and primarily X. maculata (one of the
wild platies). This process is described in
some detail in "Swordtails... for the advanced hobbyist",
Gordon and Axelrod, 1968, describing the
first red swordtails seen
by anyone in 1922. In 2010, pure swordtails or platies of any species
are
no longer seen in pet stores, yet many are as brightly
colored and even larger than their pet store
cousins.
Through this careful breeding process
the beautiful fish created by those efforts lost some
aspects of their wild form, most notably the long (and on a few, very
long) swords found on
the X. helleri.
Not found in the pet hobby are the swords carried by a number of wild
species,
such as the
X. montezumae,
X. clemenciae, X. mayae,
X. malinche, X. nezahualcoyotl,
X. alvarezi and X.
signum species, all of which are kept today by specialty
hobbyists.
The swordtails I refer to here, and
that comprise most all of the fish we generally think of as
swordtails, will be from the Xiphophorus genus. For more specific
information see
"Atlas
of Livebearers of the World".
Well known to science, the
swordtail Xiphophorus helleri was one of the first
animals to have its
genome fully mapped over the
course of its use in cancer research. Various populations possess
black spotting that through breeding manipulation can be triggered to
become cancerous, and have
been a resource for
the study of melanoma since the mid 1950s. A number of wild X. helleri
populations have been collected and introduced to the hobby,
but many eventually disappear.
Two recent introductions are being bred out here so that they
can be maintained and kept in the
hobby long term, the X.
helleri Rio Otapa, and the X. Helleri
guentheri Belize "Golden Stream".
It
is assumed that the long sword has been developed to attract females. In
courtship behavior, the
male will repeatedly swim
around the female, who chooses to breed, in part, with the largest
individuals.
The sword extension seems to cause
the male carrying it to appear larger to the female, resulting in
increased matings with the males carrying the longest swords.
There are also a number of swordtails with short swords, that are also
very attractive but that are not
very often seen
in the hobby. These would include the X. cortezi,
X. nigrensis, X. multilineatus,
X. andersi, among others, including new species still
being discovered and identified.
Indigenous
to Mexico, various species can be found throughout Central America, and
at various
elevations, though certain aspects of
their husbandry can be assumed. They prefer
clean water with
some water movement as they evolved as
wild fish in streams and relatively shallow water
environments that also contain plants.
Depending on species, the
temperatures preferred are
cooler than where
they are generally kept by the average hobbyist, who was introduced to
swordtails
through those available in the
commercial hobby. Most pet shop fish are kept between 75 and 80
degrees, when in fact swordtails will grow larger, live longer and
reproduce more consistently at
closer to 72
degrees.
Gestation is around 30 days for all
swords, depending on temperature. Fry
are about 6-7mm, and
can take
brine shrimp from birth. All
swordtails are opportunistic fry eaters, and the females need to
be removed from the adult population to have their young. A generation
is about 8 months, and the
young males do not
begin to develop their sword until 3-4 months. Sexing young fish is done
by
identifying a gonopodium on the males, or the
darker gravid spot area on the females. Mature
males can be territorial with other males, and may spar and chase one
another, though injuries
are rare.
It is thought that larger males release a growth inhibitor into the
water that only affects other
maturing males,
though this substance, if it exists, has never been identified. When
raising them
to develop maximum size it is best
to raise the sexes separately with generous
water changes
and abundant live foods, particularly
red worms, black worms,
daphnia and adult
brine shrimp.
See "How to Raise BIG Fish". However, you
cannot take a fish that has grown up in a warmer
environment and immediately move them into a tank that is 72 degrees, or
the fish may become
sick, most likely with a bout of
ich, or "white spot disease". To
accustom these fish to cooler
temperatures,
slowly acclimate them by lowering the
heater in their tank by a
quarter turn no
more than once a week. You can
then gradually acclimate them to cooler temps over time,
avoiding disease. Be sure to
accompany this process with regular water changes and
frequent feeding. All of the fish
raised by select aquatics are raised at 70-76 degrees,
depending on the season.
Swordtails are also rumored to
change sex, which they cannot do. However, many species of
swordtails produce early maturing males that sex out early,
giving them a reproductive advantage
over their siblings. Alternatively, the largest, dominant
males take much longer to reach sexual
maturity, when overall body growth stops. Until then they may
be identical to other females.
Older females may also develop some secondary male sexual
characteristics as they age,
but they are never fertile.
Swordtails and
Size:
Lastly, swordtails are often the topic of stories told regarding how big
some fish used to be, or
can get, or that someone
once saw. I remember well growing up and hearing stories of male red
swords bred in the 1960s that reached body lengths (not including sword)
of 6 inches or more.
Recently, I had a
scientist friend who is well known in the hobby decide that he was
going to raise
an
X. montezumae
to the largest it can possibly become. It has been rumored that this
fish can
become 10 inches! He put no more than 3
males each in 2- 30 gallon tanks,
fed them heavily on
daphnia, various worms and dry
food. At about 6 months, I flew out to East to see what he was
doing and took pictures of them. See the pic of them
here. They were becoming huge, fat fish.
After about a year, he called me to say that someone had come to look at
them, and estimated
their length at 9 inches,
though he did not measure them himself. He said he was about to destroy
them because he needed the tanks they were in. I
asked him to put them in alcohol and send them
to
me, which he did.
I laid them out against a
ruler, and they were 5.5 inches, from the tip of the nose to the end tip
of
the sword. They were very husky with a high
back, giving them the appearance that they were much
larger than they actually were. I have kept this species for many years,
and now offer a population of
Tomosopo monties
here. They are routinely a fairly large fish (though not as large, or as
brightly
colored as the X. mayae), and over the
years I have measured older specimens often. They would
generally reach their maximum size at just about 5- 5.5 inches.
I do not doubt
that 6 to10 inch swordtails may exist in the wild, but I am skeptical
that there were ever
fish of that size in the
commercial hobby. I have seen mollies raised to that size (about 6
inches)
by a commercial fish farmer who also
breeds his fish for size. If you would like to attempt to raise
one of these swords to those large sizes that you don't see anymore, the
X. mayae is an excellent
candidate. Without question all of these swords are impressive in a show
aquarium.
And which species has the longest
sword? Without question, the Xiphophorus montezumae,
whose sword is routinely 1.5 times its body length, and will often sport
a sword twice its body length!
_______________________________________________________________________
A Slightly different Approach to Buying Swordtails
Raising Swordtails,
particularly to get them to a large size, has led to unexpected issues.
Many of the swords sold here will routinely grow to over 4
inches, and some will pass 6 inches.
Over the past 2 years we have attempted to raise large
numbers of X. mayae, for example, that
could be sold at about 3 inches, that were clearly going to
be exceptionally large fish. We found
that it is simply is not possible to keep the stocking levels
low enough, the feeding schedule
heavy enough, and still produce enough fish to meet orders.
Many tanks of 40 and 50 gallons
were tried to find the right stocking level to get the
maximum growth from every fish in the tank
throughout their lives. It was found that maximum growth
continues only when they are moved
to much lower density tanks at about 3-4 months old, and then
fed heavily, with moderate aeration,
adequate filtration, and water changes from that point on.
For this reason, the X. mayae,
X. montezumae,
X. alvarezi and X. helleri populations
will be sold
primarily as recently sexed out pairs (4-6 months), or as
groups of 6 young. The swords shipped
will be chosen for potential to become large individuals.
Extras can then continue to be shipped
with each order, and the fish will arrive at the best time in
their lives to adapt to new
conditions, while still young enough that their breeding
capabilities are ahead of them. Most
customers prefer fish of this size anyway, but for those
looking for fully grown, older fish,
I will have them available only occasionally.
As full sized adults become available, they will be offered
at Aquabid or by request.
Selecting for larger fish as they reach sexual maturity
somewhat guarantees that you are
receiving fish with the potential to reach a large, healthy
size. Nothing compares to fish raised
under optimum conditions, and rows of tanks containing
hundreds of fish, as is the case here,
cannot duplicate what you can do with a few pairs in a 50
gallon tank, lightly planted with frequent
feedings of quality food. I want to be sure the fish you
receive have not had their growth slowed,
or stunted in any way, so that with proper care they will
grow for you as large as they are meant to.
________________________________________________________________________________________
More on Size and Breeding Patterns in Swordtails
One more point to mention is that a pair of large fish do not
necessarily produce all young that will
grow as large as their parents. This is especially true with
recently wild fish, or fish that have been
allowed to community breed over a number of generations.
Careful selective breeding can develop
lines that routinely grow large, but even then the variety of
overall size attained by the males can
span a wide range. Of a batch of 30 fry, say, of the wild
X. mayae, for example, this is approximately
what you will receive:
Water temperatures
and pH of the water in your fishroom will affect the ratio, but this
species
roughly produces 50/50 males to females. So we will assume
there will be 15 males, 15 females.
Since for right now we are interested in large males (and
females are generally far more consistent
in their growth and overall size), we will look at just the
15 males.
- Of those 15 males 3 or 4 will be "early maturing" in that
they will begin to develop a sword earlier
than their brothers and cease overall growth for size at 4-5
months, topping out at about 3.5 inches.
- 5-6 of them will take especially long to mature and with
proper feeding and water changes will grow
out to become very large fish. It may take 8-10 months for
them to reach full size, and they will
continue to slowly put on size throughout their lives. There
are fish here that have lived for close to
4 years. The largest male X. mayae here is the large very red
male shown in the videos, and is
currently about 6 1/4 inches, including the sword.
- The remaining 5-7 fish will be large full sized males that
will top out at 4.5- 5 inches, and will be
ready to breed at about 6 months.
These ratios roughly work for most of the wild swordtails,
including the X. mayae,
X. montezumae
and X. helleri. With the
domestic lines, culling the early maturing males and only breeding the
largest
males, over a number of generations, does increase the
consistency of production of large males.
However, other traits often begin to appear, and the purity
of the wild genotype will be lost, creating
fish that become domestic, selectively bred versions of the
wild form.
I have had customers ask for "only fish over 5 inches",
without realizing that not only are they
requesting older fish, they are not truly receiving
representatives of the wild fish they desire. When
choosing the young, recently sexed out fish to send to
customers, I do remove early maturing males,
and choose those sent from those remaining. The fish sent out
are chosen for overall robust health
and good color. Swordtails require that large numbers are
bred so that customers only receive the
best examples, and of all those raised, easily a third will
never be sold due to the natural variation
in size and color that these fish exhibit.
Customers write that they have been disappointed in the past
with fish they had received from other
breeders, in that they felt they were undersized, when in
fact they were simply receiving fish that were
born from from a pair or two the other breeder maintained,
and the breeder simply sent what he/she had,
and they were perfectly fine fish. I will always strive to
send the largest, healthiest fish possible, but am
able to do so because they are raised here in larger numbers.
Over time we have gradually developed
fairly large strains of the fish we maintain, but smaller
fish and early maturing males are the normal means
of reproduction for these fish, and as you breed them you
will want to remove the smaller individuals that
can influence the size of your line over time.
I hope this clears up some confusion, as I wish to offer as
many species as possible of healthy,
full sized fish that live long lives after arriving in
your tank! If you have any questions, simply
email me at
selectaquatics@gmail.com .
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