the females, and will show little interest
in guarding the eggs or fry. Basic care is
otherwise similar to N. brevis.
Inexperienced aquarists are often
advised to avoid the pencilfish of the genus
Nannostomus. While they are certainly
pretty and peaceful, they are sensitive to
water chemistry and often fail to adapt
to busy community aquaria. The one
notable exception is the golden pencilfish
The golden pencilfish is a small, slender
fish that gets to about 2 inches in length.
Its basic color is golden green with several
blue-black bands running from nose to tail
and brilliant red markings on the anal and
tail fins. Golden pencilfish need to be kept
in groups of six or more specimens. Males
are distinctly territorial though, and will
spend a lot of time chasing one another.
No harm is ever done, and their boisterous
antics really only add to their charm.
Because pencilfish move about in a slow,
rather deliberate sort of way, they work well
in small planted tanks. Golden pencilfish
are adaptable and will eat all sorts of
foods, including flakes, something that
cannot be said for most other pencilfish.
Also unlike most other pencilfish, golden
pencilfish will adapt successfully to hard,
alkaline water conditions. All in all, they
make an excellent alternative to the more
commonly kept characins.
Nannostomus beckfordi is a small, adaptable pencilfish that will accept most standard aquarium
foods, such as flakes.
#7: Least Killifish
The least killifish is, despite its name,
a livebearer and not a killifish at all. It is
one of the smallest fish known to science,
and a native of the southern United States.
Males are slightly less than an inch in
length, females about 1½ inches. Both
sexes are rather similar in looks, being
semi-transparent silvery green with a dark
band running from behind the eye to the
base of the tail. There are distinctive black
blotches on the anal and dorsal fins.
The least killifish is not a difficult fish to
keep, despite its miniscule size. It prefers
hard and alkaline fresh water, but will
also do well in slightly brackish systems.
As a subtropical fish, it doesn’t need a
great deal of warmth, and could be kept
in an unheated tank in the warmer parts
of the world. Feeding this fish couldn’t be
simpler: flake, algae, and small live foods
such as Daphnia are all readily taken. The
least killifish appreciates a thickly planted
The “least killifish” Heterandria formosa is actually a tiny livebearer.
aquarium. Floating plants are especially has proven to be easy to breed, and farmed
useful as cover for newborn fish, which fish are now widely available.
are tiny and at severe risk of being eaten C. margaritatus has a blue-green body
by any carnivorous tankmates. covered with small cream-colored spots.
The fins are marked with red and black
stripes. Males have brighter colors than
females, but otherwise the two sexes are
similar. They are shy, and need to be kept
as a group in a well-planted aquarium.
C. margaritatus is rather surprising in
its needs; it’s a fish that prefers cool,
hard, slightly alkaline water rather than
the warm, soft, acidic water we tend to
associate with Southeast Asian fish. Its
tiny adult size of well under an inch makes
it a viable schooling fish for the small
aquarium despite being quite active.
Initially known as the galaxy rasbora
Microrasbora sp. “galaxy” but now properly
called the celestial pearl danio Celestichthys
margaritatus, this lovely fish was discovered
in Burma in 2006, and quickly became a
hit among fishkeepers around the world.
Because wild populations turned out to
be small and vulnerable to extinction,
the Burmese government has restricted
exports of wild fish, but C. margaritatus