C. kelberi and C. piquiti - Report by Dr. Stuart Willis
We fished for these near Sao Felix, where the Rio das Mortes encounters the Araguaia. This is a clear, sandy, low-gradient, meandering floodplain river, with many lagoons and channels.  C. piquiti and C. kelberi seem to divide ecological space not unlike C. temensis and C. monoculus in the Negro, or C. temensis and C. orinocensis in the Orinoco.  That is, C. piquiti are larger, appear to occupy deeper habitats with more flow (e.g. channels), while C. kelberi are more often in smaller, shallower or lentic habitats (e.g. lagoons). We caught both on silver weedless spoons, my standard fare (the idiot-proof lure, I guess).  Locals called these fishes tucunare branca (C. piquiti), and tucunare amarehla (C. kelberi), and only the large, sexually mature C. piquiti acquire the bluish fins, and hence the appellation tucunare azul (like the acu C. temensis).