swampy, soupy shore of a lake. This tiny
fish leaves the open waters to Gambusia
livebearers and larger fish. Here in the
weedy shallows, though, it was thriving,
and hidden away, for the most part, from
predators (i.e., every other fish, aquatic
birds, and water snakes), and sustained by
a microorganism salad bar.
This water was calcium hard, but regional
populations have been found in relatively
soft or brackish environs as well. They came
home with me in water bottles (of which I
think I might have drunk one). Note: The
TSA does not allow water bottles to be
taken through screening any longer—you
will have to drink your bottled H. formosa
before you go through security.
An Ideal Desktop
or Tub Pond Fish
My above biotope observation helped me
understand why H. formosa is such a hardy
charge in the home aquarium and outdoor
tub pond, and also why it can withstand
lower oxygen levels than other poeciliids.
Being subtropical in its native range, it can be
maintained from 60° to 80°F, with temporary
changes to higher or lower temperatures well
tolerated, in my experience. I recommend
calcium-hard water ( 15 to 20 degrees) and
temperatures of at least 70°F to ensure spring
and summer breeding.
I have established a H. formosa colony
in a one-gallon desktop aquarium with no
filtration other than live plants, as well as
small outdoor water features. They are a great
summer tub fish! Larger vessels will ensure
a colony. They are shy, though, preferring
to hide near the bottom among gravel
pieces and plants. Males can occasionally
be observed sparring with each other with
their gonopodiums or snouts. They do not
display any noticeable courtship behavior
that I or anyone else have read or observed.
For an aquarium setup, I recommend Java
moss to offer security and a medium for
microorganisms for the fish to feed upon.
Tropical hornwort in midwater and floating
on top of the tank also offers security. Do
not make the light too bright or, if that’s not
possible, use floating plants. A thicket of
Vallisneria or small Cryptocoryne wendtii, I
find, offers the best compromise for viewing
versus security. If these live plants are not
available, plastic plants and breeding grass
can be used.
For outdoor tub ponds, water hyacinth
and/or a hardy water lily are inexpensive
ways to shade their environment. Water
Dwarf livebearers Heterandria formosa, male above, female below.
In their native habitat H. formosa are found in the vegetation-rich shallows and prefer a well-planted aquarium.
hyacinth, in particular, is a very good filter
(just disinfect overnight with a fluke tablet
dip to remove possible hydra. Thanks to
Rosario LaCorte for this tip—get well,
Aside from its size, this species differs
from most other poeciliids in two key
respects. Both relate to the fish’s reproductive
abilities. Like most poecilids, H. formosa
females have the ability to store sperm from
males for subsequent matings. But instead
of utilizing a sperm packet all at once like
other poeciliids, in a regular 28- to 40-day
cycle of fertilization to birth, H. formosa
practices superfetation: There will be fry in
all stages of development within the mother,
with one or two being born every day.
In this way a tiny fish is able to produce
remarkably large babies. Another important
aspect of this fish’s reproductive biology is
that the mother provides supplementary
nourishment and gas exchange to the
fertilized eggs via a placenta-like membrane
Tropical Fish Hobbyist www.tfhmagazine.com