I spent a few days in Manaus, and another week moving on the river, in 2004 when I lived in Carmo do Paranaiba, Minas Gerais for a year. A very beautiful place, but very hot, and very humid. The air seems to have a weight and a thickness. Would love to have been a fishkeeper there. I do have many photos of native wildlife though.
Lets see some photos of the tanks. Think you could take some photos of the shop you got to? (storefront and tanks and fish pics, o my).
What kind of success ratio do you have from the fish you catch? Do they acclimate well? Are there any reoccuring problems you have with the fish you have lost?