i think it was a female, but i just found it laying on the bottom, it wasnt tore up or anything. and it didnt look sick before, so i donno what happened. now i guess i need another female for the male sailfin.
Actually, you don't really need to have a female in with a male. If you are not breeding, there isn't a need for a pair.
Stress might have been the cause of death. It seems as though you only had one female in with the male, so he might have pestered her to the point where she was overwhelmed by the stress.
What size tank and what were the water parameters?