flies are good. Do not use whole beetles unless your fish are large. Beetles can be very good but you may have to grind them up. chopped earthworms are good too.
Every species is somewhat different. There some usual things like the male will have longer more pointed fins, The males of most species are more colorful when adults. Adult females will usually exhibit a more rounded midsection. In live bearing species the male will have a gonopodium which...