Got this from another forum.
OK... so what is the fish you have in your tank that you thought was a regular Festivum?
Well, the answer depends on where it is from. Mesonauta insignis (the type species of the genus) is found in the Rio Negro and Rio Orinoco. This is what gets exported out of Manaus and Barcelos, Brazil. Distinguishing character: of the 7 faint vertical bars that these fish exhibit when stressed, 2 and 4 are joined and the scales above the diagonal "flag" bar are reticulated.
M. egregius is found in Rio Meta, Colombia. It is occasionally seen on price lists of fish from Colombia as Festivum. Distinguishing character: bar 3 divided into two.
It is quite certainly M mirificus if it was collected anywhere near Iquitos, or Pebas, Peru. Distinguishing character: divided bar 3 and there are think horizontal lines above the diagonal flag bar.
Southern Peru (Rio Madre de Dios), Bolivia and in Paraguay has the true M. festivus. Unfortunately, this is not a hotbed of aquarium fish export and so, it is unlikely that most of us ever had the real "Festivum" - kinda like the story with Geophagus surinamensis. Distinguishing character: bars 5 and 6 are joined.
Rio Xingu and Tocantins have M. acora. Despite increased collection in these two rivers, attention is mainly focused on colorful Loricariids and Pike cichlids. Thus, M. acora is unlikely to be found in your tank. Distinguishing character: divided bar 4
The latest (and most likely not the last) addition to the genus is the fish that was exported into the hobby so often in the 50's and 60's from Guyana, Mesonauta guyanae (Schindler, 1998) described from the Essequibo River in Guyana. There is limited export from Georgetown and so, you are certainly likely to have M. guyanae. I have yet to read any commentary on the authenticity of the status of this new species from other ichthyologists (read: Kullander)
How nice and complicated! Some don't care what species they have and others do. When comfortable, the said bars are not very visible on these fish. You can always put them in a plastic bag and shake them up a bit and wait for the fright patterns to emerge - you can tell pretty easily then. Cruel? Uh-huh. Effective? Certainly. You decide.
I'll find the other page with info a bit later, on my way out now!
