red tail sharks

#3
Agreed. RTBS's are highly territorial with eachother regardless of gender.
They also don't like other fish that closely resemble them (rainbow sharks, black sharks, flying foxes, SAE's, other bottom-dwelling cyprinids)
Keeping a male and female together wouldn't result in much anyway. They don't spawn readily in the home aquarium, if at all. Most are bred using hormones that are injected into the fish to get the to spawn.