Visual inspection of the fish in hand should be adequate once they're large enough (5 inches is about the earliest that I've been able to tell apart). Males have a small V shape because their breeding tube is more narrow. Females have a wider, O shape since their breeding tubes are wider. So if you were looking at the fish, it'd be:
o > Male
o O Female
(They both have anuses, which is the little o shape)
You can't always tell by fin shape or nuchal hump -- I had a mono-ocell hybrid that the most amazing pointed anal fin, and some padding in the nuchal hump area that I thought for sure was male, but was sitting on top of a clutch of eggs one day when I came home from work!