Hard to give you more info just based on that. Tapajos is a river in Brazil, not a species of fish. It is sometimes included after a species name to indicate the locality where the fish originated but could be applied to a bunch of different fish.
Eg. are they Geophagus sp. tapajos red? Or Crenicichla sp. tapajos?
I have a fisherman and a biologist friend that lives next to Tapajos river, there in Amazon, Brazil. It is a clear water river (if you would say that Amazon river is reddish...) The pH is a little under 7.0. If you send me the picture of the fish, I can help identify it. banana94b@gmail.com
Tapajos river. That is were P-14 (P. Potamotrygon stingrays) are from. And in discussion if the USFWS will indicate the specie to be include at Appendice II of the CITES. (Next CITES meeting, probably a the first half of March 2009, there at Doha city, Qatar)