Nannostomus marilynae,, commonly known as Marilyn's or greenstripe pencilfish, is a freshwater species of fish belonging to the characin family Lebiasinidae.
Should ideally be kept in a heavily-planted set-up, preferably with a dark substrate.
The broken lines of sight that exist in such a display allow it to display natural behaviour as well as helping to reduce skittishness.
Floating plants are a useful addition as are driftwood branches and dried leaf litter, the latter in particular driving establishment of microbe colonies as decomposition occurs.
Such microorganisms can provide a valuable secondary food source for fry, whilst the tannins and other chemicals released by the decaying leaves are also thought beneficial.
Filtration need only be gentle with an air-powered sponge-style unit normally adequate, though a degree of water movement is acceptable.