Nannostomus mortenthaleri; plenty of open swimming space is needed for pencilfish, which occupy the upper to middle regions of the tank.
same physical and chemical parameters.
Well-fed fish reach around 1 cm (½ inch)
at about two months, after which they
begin to develop adult coloration.
Nannostomus mortenthaleri does not
spawn as frequently as the other species.
Distinguishing the sexes depends on the
fact that the red rim on the male’s anal
fin is darker than that on the female’s.
A mature pair should be transferred to
a spawning tank, ideally at the time
when the male changes color to dark
purple, which is a signal that spawning
is imminent. As in the previous case, it
is best to separate the pairs that have
already laid eggs from the rest of the
fish, and immediately before spawning
isolate the pair from each other (for 7 to
10 days) and feed them generously with
quality live food, which will increase
their willingness to spawn and, later, the
number of fry.
During the spawning itself, the male
makes swinging movements, assumes
a head-down position, and his color
changes from purple to blood red. The
pair press against each other, and after a
moment of trembling, an egg (sometimes
two) falls to the bottom. Usually there are
about 30 eggs; the unfertilized ones will
disintegrate in time.
Tropical Fish Hobbyist www.tfhmagazine.com 69
A well-planted tank brings out the best colors in Nannostomus marginatus and makes the fish
feel more secure.