I realize this is an old thread, but the same question keeps popping up.
Just because one individual or group from one river looks different than another group from another river does not make it a different species.
The topography or turbidity of one river may induce characteristics to develop to fit habitat.
Here's another example of one species, where different location calls for a different look (color, even other slightly different features, such a head shape).
Chuco intermedia
below Chuco intermedia from a river not that far away from the first, but different topography
Just because one individual or group from one river looks different than another group from another river does not make it a different species.
The topography or turbidity of one river may induce characteristics to develop to fit habitat.
Here's another example of one species, where different location calls for a different look (color, even other slightly different features, such a head shape).
Chuco intermedia
below Chuco intermedia from a river not that far away from the first, but different topography
