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First, I consider Practical Fishkeeping an excellent magazine, but in this case I believe that they might be wrong. If they are only considering scientifically described species, they may be correct. A. angayuara is known from preserved specimen to grow to 24.7 mm/1" SL (without caudal fin). There is a scientifically described species that is smaller. This is A. parva Ahl 1931. This species is only 22 mm/⅞" TL (with tail!). It is true that A. parva is presently considered"sp. inquirendae" or a "questionable species". It might be a juvenile of an elongate species. The only elongated species that I know about that comes from the Rio Capim is A. cf. agassizii Broad Black Caudal Seam (Tocantins). If this turns out to be true, A. angayuara is much smaller.
Since wild fish are commonly much smaller than those of the same species kept in aquariums, I imagine that A. angayuara will get larger. There is some debate whether or not A. sp. Kupferrücken/Copper-back is A. angayuara or A. inornata. If Kupferrücken is A. inornata, then it grows to 4 cm/1⅜" TL. If Kupferrücken actually is A. angayuara, then angayuara grows to 6 cm/2¼". If A. angayuara is neither A. inornata not the Kupferrücken Apisto, then it might be the smallest apisto known, but we will have to wait until it is kept under aquarium conditions. For me the smallest known apisto is still A. sp. Balzfleck/Courting-spot in which the females grow larger than the males - 3.5 cm/1½" TL.
The DATZ book has a picture of the preserved holotype of A. angayuara listed as A. sp. "Trombetas 1" (A. salpinction is listed as A. sp. "Trombetas 2").