Looks female to me. I'm no expert on JDs though. Maybe he chases her being the 2nd in charge of the tank? Biggest threat to food source? I don't know. Cramped living space? Different species but my male rivulatus have chased off females for no rime or reason. They always have really, except for ones that have truly paired off. That said though it's nothing like having two males in a tank where there's really battling going on and no tolerance for the other.

