This is a discussion on Is it a boy or girl? within the Characins forums, part of the Freshwater and Tropical Fish category; -->
I have 3 bloodfin tetras and wanted to know which were boys and which were girls... and I do not know how to tell ...
As with many of the characins the mature female is rounder than the male. With this species, Aphyocharax anisitsi, the male is slightly more colourful and has a small hook on the anal fin.
They should be kept in a group of 6 or more as they are a shoaling species (like most tetras) and will always fare better (and be more likely to spawn if that is your desire) when kept in groups. They can live for more than ten years in good conditions.