My experiences with Swordtail Characins
by Don Murray
From the Monthly Bulletin of the Hamilton and District Aquarium Society
Aquarticles
On a visit to one of our local pet shops last spring, I discovered a fish I could not
remember having seen before. It was small, about one inch in overall length, and a very
active swimmer with a generally silver colouring. The fish I took to be a male had a
number of elongated yellow rays in his lower caudal fin as well as a dark spot near the
centre of his body above the anal fin. This "spot" appeared to move around as
the fish changed direction as it darted through the tank. I decided to take some of these
unusual little fish home for further study.
I put my new fish in a 50 gallon community tank along with angel fish, Congo tetras and
other, I hoped, compatible species. They have become upstanding and attractive members of
the tank as they dart about in search of food or in playful pursuit of each other.
It didn't take too long to discover that the spot on the side of the male swordtail was
attached to his gill plate by an almost invisible thread-like spine. He would at times
take up a position about an inch in front of the female and, with a fluttering motion,
fling this spot, or spatula as it more aptly appears, out before her.This action seemed to
cause her little, if any, concern.
On searching for information about this, new to me, species, I discovered a short
article in the May 1976 TFH about it and some related species, all of which are found in
South America. This article further identified my swordtail characin as Corynopoma
riisei. It also described the male exciting the female during courtship by stroking
her with the spiny extensions of his gill covers, or spatula, as I have come to think of
them. I have yet to observe this stroking behaviour or for that matter any other physical
contact among my specimens. Apparently, in contrast to what happens with most egg laying
species, the male transfers a packet of sperm to the female instead of releasing it into
the water.
Upon indulging a habit that I picked up somewhere over the years of going through the
books and bulletins at the pet shops, I came upon an article that described the apparent
oral insemination of the female, with the eggs being deposited by her alone at a later
time of her choosing. I regret not being able to recall the book in which I found this
quite good article.
Having all of this information, I decided to try raising some of these interesting
little fish. I installed my female, now about 1½" overall, in a 2½ gallon tank.
Included in the set-up was some hygrophila and a bit of long fibre sphagnum moss. The moss
gradually settled and covered the bottom of the tank. I used ordinary local tap water with
a pH of 7.2 to 7.4 and a TH of 150 to 180 ppm, kept at a temperature of 78F. I fed her
abundantly on live foods, including white worms, fruit flies and tubifex worms.
On the tenth day I discovered, on observation with a flashlight, a number of tiny
silver slivers darting among the hygrophila and the debris of the sphagnum moss. I removed
the female. The fry seemed to be of different sizes, indicating that they had been
hatching for several days and also that the mother probably had not been eating them.
I began feeding them at once, alternating with two different brands of micro-ground fry
formulas. My brood increased in numbers daily until a week later I estimated the number at
75. At this time I began feeding newly hatched brine shrimp several times a day along with
the fry formulas which I maintained for the newest hatchlings.
Ten weeks from spawning I have not lost any of my little swordtails. They form an
impressive school of active silvery fish swimming in a forty gallon community tank along
with fry of several other unrelated species. They are generally silver in colour with
flashes of metallic blue, pink and orange as the dart about. The rays of their caudal fins
are light yellow and no sexual differences are yet apparent. These hardy little fry are
growing steadily on a varied diet of scraped beef heart mixture, chopped worms and some
newly hatched brine shrimp.
As I observe my Corynopoma riisei I cannot help wondering why they haven't
become more popular in the aquarium trade. They seem to be at least as hardy and
attractive as the ever-popular danios and are as attractive and perhaps more active than
some of their more popular tetra cousins. I'm sure the interesting breeding habits of this
species also invites further study.
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