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The white background is causing the fish to "bleech" their color pattern. Can you get us a pic of the fish settled in over a neutral substrate? This looks very similar to the Rineloricaria commonly collected at Leticia.
-Shane
"My journey is at an end and the tale is told. The reader who has followed so faithfully and so far, they have the right to ask, what do I bring back? It can be summed up in three words. Concentrate upon Uganda."
Winston Churchill, My African Journey
I'm not even sure these are the same species. The shape of the pectoral fins is very different. Plus, coloration also differs and it looks like the smaller one has two filaments on the caudal while the bigger one only has one.
I think the larger one is a female R. beni, provided it is as small as I assume from the picture.
The smaller one I have no idea.