Nannostomus marginatus
By Tom Wojtech
From Splash, newsletter of the Milwaukee Aquarium Society
Aquarticles
About two years ago I found a group of Nannostomus marginatus while making my
usual trip to Pets n Things. These have been a favorite of mine for a long time. They used
to be a fairly regular import but it had been years since I had seen any for sale. I ended
up getting a group of eight. I only had a bare 10-gallon tank available on the low row of
tanks so this would be their temporary home.
Nannostomus marginatus is one of the smaller pencilfish and one of the nicest.
They have two longitudinal black stripes on a creamy body with a hint of red near the tail
end. The fins are edged in black with brilliant red in the center when they are happy.
They are a schooling fish so you will see the group glide through the tank in single file
or bunch up to feed. The males will select a territory and try to entice females to spawn
and square off at other males. They do this in a rather gentle manner and generally for a
short time going back to a cohesive school easily.
My temporary tank lasted for two years. I was cleaning one day and noticed I had three
left. Due to my crummy back I didn’t spend much time crawling on the floor in order
to get a good look at the tank. I did keep them in 80% RO water and did feed live baby
brine but never made any attempt to breed them. The small bunch of Java moss had grown to
take over half the tank. I had not been able to keep up with water changes and green algae
covered the Java moss.
One day when I was feeding, I thought I noticed a group of pencils swim into the moss
when I came towards the tank. I went through my feeding routine and then lay down on the
floor to watch their tank. It took a couple minutes but slowly a group of baby marginatus
came out to eat. There were a couple only just starting to show a stripe, which I figured
were about 3 weeks old, and a few more about half an inch, which had to be nearly 2 months
old. I have seen about 10 fry so far. This prompted me to try to ensure their survival so
I did a good cleaning and water change.
This was a basically bare tank but while cleaning I found out that much of the Java
moss had died from being choked by the algae. This must have caused the pH to drop and
made the tank acid enough to support breeding. I was surprised to see any babies from
these two-year-old fish since most tetras spawn better and easier as young adults.
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