Origin
Pterophyllum altum probably does not occur in eastern tributaries of the Orinoco, or in the Rio Negro, or in any other portions of the Amazon basin, according to several of today's experts. The fact remains, however, that at least one collection reports it from the Rio Negro.
If P. altum has indeed crossed from the Orinoco drainage into the Rio Negro, il would have been through a legendary natural connection called the Rio Casiguiare, or the Casiquiare Canal. This high water bridge between the two great rivers was made famous by Alexander von Humboldt, who described it as a fast-moving tributary river of the upper Orinoco that was captured through
I'terophyHum ailimi. the loll aiigclfish.
land subsidence, causing it to change direction from its original route northward into the Orinoco to its present flow regime, southward into the Rio Negro. This was a dramatic example of stream capture on a massive scale. Later, Alexander Hamilton Rice, the father of photo-grammetry, photographed the relationship of the three rivers (Rio Casiquiare, Rio Negro, and Rio Orinoco) from the air. On his last trip in 1924-1925, it is said he ascended the Orinoco River to its headwaters, traversed the natural Casiquiare Canal, and descended the Rio Negro into the Rio Branco, and then continued to the main stem of the Amazon at Manaus. The likelihood of further collections in this area to validate distributions is remote, as the area is now part of the Upper Orinoco/Casiquiare Biosphere Reserve set aside for the stone-age Yancimami native people. The area today is accessible only by foot path or by helicopter, and only by government permit.
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