It varies, but usually settles out after dominance issues are settled. It's not unusual to see peaceful "poly piles" even with different species sometimes. Definitely more common with same or closely related species though.
Might want to look at sand or bare bottom, especially with little guys. They don't see too well and have been know to swallow gravel. If they aren't big enough to pass it, it's usually fatal(the other option is barfing it back up.)
Might want to look at sand or bare bottom, especially with little guys. They don't see too well and have been know to swallow gravel. If they aren't big enough to pass it, it's usually fatal(the other option is barfing it back up.)