I bought a trio of bushynose plecos with intentions to breed them. Little did I know these guys are predatory!! I've kept these guys countless times but never had them EAT another fish. So they're up for sale. $15 picked up and they're yours.
It is rather odd that a bn would actively hunt, unless it was starving for food. It is more likely that the swordtail just died, and they chewed on the carcass.