Factsheet 3

Nannostomus marylinae

The eminent ichthyologist Carl Ternetz originally found Nannostomus marylinae in February 1925 in the Rio Negro. He did not describe the holotypes, possibly mistaking the fish for Nannostomus trifasciatus. The ‘night’ colour pattern is quite different to that of N. trifasciatus whilst the ‘day’ colour shows more resemblance to N. minimus. In 1974, Weitzman & Cobb1, received 190 live specimens collected in Columbia and these provided confirmation of their findings when examining the Ternetz specimens.

Nannostomus marilynae was named after Dr. Weizman’s wife Marilyn Sohner Weitzman who shared the love of the members of the genus Nannostomus.

I was very fortunate in obtaining 12 very small specimens when visiting Holland in 2000. Prior to that, I have no reason to believe that this species was imported into the UK. The fish were housed in a 10-gallon tank with soft water and well planted. They settled in well and were soon taking a full range of live and dried foods. When they reached c.20mm in length, it was reasonably easy to sex them and at this stage, males and females were separated for conditioning prior to spawning. Small midge larvae were accepted eagerly and after 2 weeks, the females were looking suitably rounded. Males started showing off to one another in the typical manner of most males in the genus, and gained colour.

The tank I use for spawning most pencil fishes, measures 8 x 6 x 6inches. Water is taken from each of the ‘stock’ tanks (GH 5degrees pH 7). Java Moss (Vescularai dubyana) is used as a suitable spawning medium and as a safe haven for the females. I do not normally breed fish of this genus using a flock method. I much prefer a traditional one male, one female approach since I have no desire to produce large quantities of fry.

One female is placed in the tank during the daytime, and just before I turn off the fish house lights, a male is added to the tank. Providing the fish are ready, spawning takes place in the early morning. It is better if the tank is positioned to catch the early morning sun. The fish spawn among the fronds of moss and careful observation is required so that the adults are removed as soon as possible. Failure to do so will result in them eating most of the newly laid eggs.

The eggs although quite small, are reasonably visible. After 48 hours or so, the eggs hatch and cling to the moss. They remain attached there for a further 24 hours, absorbing their yolk sacs. When they become free swimming, they require feeding with infusorians or a liquid fry food. I have generally found that I get 30 to 40 fry from a single spawning. After a few days, the fry are capable of taking newly hatched brine shrimp and/or micro worm. As soon as the fry become free swimming, I add a pre-conditioned sponge filter. My experience with all pencil fish is that they require good quality water conditions. Any signs of pollution cause the fry to die. As the fry grow, they are moved to larger aquaria to assist in growth.

As far as I am aware, no other stock of this species has been imported into the UK.


1) Weitzman & Cobb, 1975, ‘A revision of the South American fishes of the Genus Nannostomus Gunther (Family Lebiasinidae)’, Smithsonian Contributions to Zoology, No. 186

© Pete Cottle, 2003. This fact sheet may not be reproduced in any form without the permission of the author.