The males have much longer, flowing, dorsal and ventral fins with trailing fillaments. The females have rounded ends to these fins and lack the flowing/trailing fillaments.
they females are brighter and the males are paler
the females are generally bigger
Females have short beautiful fins. Males have long beautiful fins that make the female atarck to them.
That all depends upon the species of fish, Some are easy to differentiate between and others are impossible to tell.
Males have longer and fuller fins and females have shorter fins